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van der Wel PC. Solid-state nuclear magnetic resonance in the structural study of polyglutamine aggregation. Biochem Soc Trans 2024; 52:719-731. [PMID: 38563485 PMCID: PMC11088915 DOI: 10.1042/bst20230731] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Revised: 03/06/2024] [Accepted: 03/19/2024] [Indexed: 04/04/2024]
Abstract
The aggregation of proteins into amyloid-like fibrils is seen in many neurodegenerative diseases. Recent years have seen much progress in our understanding of these misfolded protein inclusions, thanks to advances in techniques such as solid-state nuclear magnetic resonance (ssNMR) spectroscopy and cryogenic electron microscopy (cryo-EM). However, multiple repeat-expansion-related disorders have presented special challenges to structural elucidation. This review discusses the special role of ssNMR analysis in the study of protein aggregates associated with CAG repeat expansion disorders. In these diseases, the misfolding and aggregation affect mutant proteins with expanded polyglutamine segments. The most common disorder, Huntington's disease (HD), is connected to the mutation of the huntingtin protein. Since the discovery of the genetic causes for HD in the 1990s, steady progress in our understanding of the role of protein aggregation has depended on the integrative and interdisciplinary use of multiple types of structural techniques. The heterogeneous and dynamic features of polyQ protein fibrils, and in particular those formed by huntingtin N-terminal fragments, have made these aggregates into challenging targets for structural analysis. ssNMR has offered unique insights into many aspects of these amyloid-like aggregates. These include the atomic-level structure of the polyglutamine core, but also measurements of dynamics and solvent accessibility of the non-core flanking domains of these fibrils' fuzzy coats. The obtained structural insights shed new light on pathogenic mechanisms behind this and other protein misfolding diseases.
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Pandey NK, Varkey J, Ajayan A, George G, Chen J, Langen R. Fluorescent protein tagging promotes phase separation and alters the aggregation pathway of huntingtin exon-1. J Biol Chem 2024; 300:105585. [PMID: 38141760 PMCID: PMC10825056 DOI: 10.1016/j.jbc.2023.105585] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 12/11/2023] [Accepted: 12/13/2023] [Indexed: 12/25/2023] Open
Abstract
Fluorescent protein tags are convenient tools for tracking the aggregation states of amyloidogenic or phase separating proteins, but the effect of the tags is often not well understood. Here, we investigated the impact of a C-terminal red fluorescent protein (RFP) tag on the phase separation of huntingtin exon-1 (Httex1), an N-terminal portion of the huntingtin protein that aggregates in Huntington's disease. We found that the RFP-tagged Httex1 rapidly formed micron-sized, phase separated states in the presence of a crowding agent. The formed structures had a rounded appearance and were highly dynamic according to electron paramagnetic resonance and fluorescence recovery after photobleaching, suggesting that the phase separated state was largely liquid in nature. Remarkably, the untagged protein did not undergo any detectable liquid condensate formation under the same conditions. In addition to strongly promoting liquid-liquid phase separation, the RFP tag also facilitated fibril formation, as the tag-dependent liquid condensates rapidly underwent a liquid-to-solid transition. The rate of fibril formation under these conditions was significantly faster than that of the untagged protein. When expressed in cells, the RFP-tagged Httex1 formed larger aggregates with different antibody staining patterns compared to untagged Httex1. Collectively, these data reveal that the addition of a fluorescent protein tag significantly impacts liquid and solid phase separations of Httex1 in vitro and leads to altered aggregation in cells. Considering that the tagged Httex1 is commonly used to study the mechanisms of Httex1 misfolding and toxicity, our findings highlight the importance to validate the conclusions with untagged protein.
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Affiliation(s)
- Nitin K Pandey
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Jobin Varkey
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Anakha Ajayan
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Gincy George
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Jeannie Chen
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Ralf Langen
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA; Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
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Helabad MB, Matlahov I, Daldrop JO, Jain G, van der Wel PC, Miettinen MS. Integrative determination of the atomic structure of mutant huntingtin exon 1 fibrils from Huntington's disease. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.21.549993. [PMID: 37502911 PMCID: PMC10370190 DOI: 10.1101/2023.07.21.549993] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Neurodegeneration in Huntington's disease (HD) is accompanied by the aggregation of fragments of the mutant huntingtin protein, a biomarker of disease progression. A particular pathogenic role has been attributed to the aggregation-prone huntingtin exon 1 (HttEx1) fragment, whose polyglutamine (polyQ) segment is expanded. Unlike amyloid fibrils from Parkinson's and Alzheimer's diseases, the atomic-level structure of HttEx1 fibrils has remained unknown, limiting diagnostic and treatment efforts. We present and analyze the structure of fibrils formed by polyQ peptides and polyQ-expanded HttEx1. Atomic-resolution perspectives are enabled by an integrative analysis and unrestrained all-atom molecular dynamics (MD) simulations incorporating experimental data from electron microscopy (EM), solid-state NMR, and other techniques. Visualizing the HttEx1 subdomains in atomic detail helps explaining the biological properties of these protein aggregates, as well as paves the way for targeting them for detection and degradation.
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Affiliation(s)
- Mahdi Bagherpoor Helabad
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany
- Institute for Drug Discovery, Leipzig University Medical Center, 04103 Leipzig, Germany
| | - Irina Matlahov
- Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Jan O. Daldrop
- Fachbereich Physik, Freie Universitä t Berlin, 14195 Berlin, Germany
| | - Greeshma Jain
- Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | | | - Markus S. Miettinen
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany
- Fachbereich Physik, Freie Universitä t Berlin, 14195 Berlin, Germany
- Department of Chemistry, University of Bergen, 5007 Bergen, Norway
- Computational Biology Unit, Department of Informatics, University of Bergen, 5008 Bergen, Norway
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Bravo-Arredondo JM, Venkataraman R, Varkey J, Isas JM, Situ AJ, Xu H, Chen J, Ulmer TS, Langen R. Molecular basis of Q-length selectivity for the MW1 antibody-huntingtin interaction. J Biol Chem 2023; 299:104616. [PMID: 36931390 PMCID: PMC10124945 DOI: 10.1016/j.jbc.2023.104616] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 03/08/2023] [Accepted: 03/09/2023] [Indexed: 03/17/2023] Open
Abstract
Huntington's disease is caused by a polyglutamine (polyQ) expansion in the huntingtin protein. Huntingtin exon 1 (Httex1), as well as other naturally occurring N-terminal huntingtin fragments with expanded polyQ are prone to aggregation, forming potentially cytotoxic oligomers and fibrils. Antibodies and other N-terminal huntingtin binders are widely explored as biomarkers and possible aggregation-inhibiting therapeutics. A monoclonal antibody, MW1, is known to preferentially bind to huntingtin fragments with expanded polyQ lengths, but the molecular basis of the polyQ length specificity remains poorly understood. Using solution NMR, EPR, and other biophysical methods, we investigated the structural features of the Httex1-MW1 interaction. Rather than recognizing residual α-helical structure, which is promoted by expanded Q-lengths, MW1 caused the formation of a new, non-native, conformation in which the entire polyQ is largely extended. This non-native polyQ structure allowed the formation of large mixed Httex1-MW1 multimers (600-2900 kD), when Httex1 with pathogenic Q-length (Q46) was used. We propose that these multivalent, entropically favored interactions, are available only to proteins with longer Q-lengths and represent a major factor governing the Q-length preference of MW1. The present study reveals that it is possible to target proteins with longer Q-lengths without having to stabilize a natively favored conformation. Such mechanisms could be exploited in the design of other Q-length specific binders.
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Affiliation(s)
- Jose M Bravo-Arredondo
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Rajashree Venkataraman
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Jobin Varkey
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Jose Mario Isas
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Alan J Situ
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Hui Xu
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Jeannie Chen
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Tobias S Ulmer
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA; Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Ralf Langen
- Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA; Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
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5
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Shahpasand-Kroner H, Siddique I, Malik R, Linares GR, Ivanova MI, Ichida J, Weil T, Münch J, Sanchez-Garcia E, Klärner FG, Schrader T, Bitan G. Molecular Tweezers: Supramolecular Hosts with Broad-Spectrum Biological Applications. Pharmacol Rev 2023; 75:263-308. [PMID: 36549866 PMCID: PMC9976797 DOI: 10.1124/pharmrev.122.000654] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Revised: 10/14/2022] [Accepted: 10/19/2022] [Indexed: 12/24/2022] Open
Abstract
Lysine-selective molecular tweezers (MTs) are supramolecular host molecules displaying a remarkably broad spectrum of biologic activities. MTs act as inhibitors of the self-assembly and toxicity of amyloidogenic proteins using a unique mechanism. They destroy viral membranes and inhibit infection by enveloped viruses, such as HIV-1 and SARS-CoV-2, by mechanisms unrelated to their action on protein self-assembly. They also disrupt biofilm of Gram-positive bacteria. The efficacy and safety of MTs have been demonstrated in vitro, in cell culture, and in vivo, suggesting that these versatile compounds are attractive therapeutic candidates for various diseases, infections, and injuries. A lead compound called CLR01 has been shown to inhibit the aggregation of various amyloidogenic proteins, facilitate their clearance in vivo, prevent infection by multiple viruses, display potent anti-biofilm activity, and have a high safety margin in animal models. The inhibitory effect of CLR01 against amyloidogenic proteins is highly specific to abnormal self-assembly of amyloidogenic proteins with no disruption of normal mammalian biologic processes at the doses needed for inhibition. Therapeutic effects of CLR01 have been demonstrated in animal models of proteinopathies, lysosomal-storage diseases, and spinal-cord injury. Here we review the activity and mechanisms of action of these intriguing compounds and discuss future research directions. SIGNIFICANCE STATEMENT: Molecular tweezers are supramolecular host molecules with broad biological applications, including inhibition of abnormal protein aggregation, facilitation of lysosomal clearance of toxic aggregates, disruption of viral membranes, and interference of biofilm formation by Gram-positive bacteria. This review discusses the molecular and cellular mechanisms of action of the molecular tweezers, including the discovery of distinct mechanisms acting in vitro and in vivo, and the application of these compounds in multiple preclinical disease models.
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Affiliation(s)
- Hedieh Shahpasand-Kroner
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Ibrar Siddique
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Ravinder Malik
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Gabriel R Linares
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Magdalena I Ivanova
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Justin Ichida
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Tatjana Weil
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Jan Münch
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Elsa Sanchez-Garcia
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Frank-Gerrit Klärner
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Thomas Schrader
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
| | - Gal Bitan
- Department of Neurology, David Geffen School of Medicine (H.S.-K., I.S., R.M., G.B.), Brain Research Institute (G.B.), and Molecular Biology Institute (G.B.), University of California, Los Angeles, California; Department of Stem Cell Biology & Regenerative Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California (G.R.L., J.I.); Department of Neurology, University of Michigan, Ann Arbor, Michigan (M.I.I.); Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany (T.W., J.M.); and Department of Computational Biochemistry (E.S.-G.) and Faculty of Chemistry (F-G.K., T.S.), University of Duisburg-Essen, Essen, Germany
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6
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Khaled M, Strodel B, Sayyed-Ahmad A. Comparative molecular dynamics simulations of pathogenic and non-pathogenic huntingtin protein monomers and dimers. Front Mol Biosci 2023; 10:1143353. [PMID: 37101557 PMCID: PMC10123271 DOI: 10.3389/fmolb.2023.1143353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 03/29/2023] [Indexed: 04/28/2023] Open
Abstract
Polyglutamine expansion at the N-terminus of the huntingtin protein exon 1 (Htt-ex1) is closely associated with a number of neurodegenerative diseases, which result from the aggregation of the increased polyQ repeat. However, the underlying structures and aggregation mechanism are still poorly understood. We performed microsecond-long all-atom molecular dynamics simulations to study the folding and dimerization of Htt-ex1 (about 100 residues) with non-pathogenic and pathogenic polyQ lengths, and uncovered substantial differences. The non-pathogenic monomer adopts a long α-helix that includes most of the polyQ residues, which forms the interaction interface for dimerization, and a PPII-turn-PPII motif in the proline-rich region. In the pathogenic monomer, the polyQ region is disordered, leading to compact structures with many intra-protein interactions and the formation of short β-sheets. Dimerization can proceed via different modes, where those involving the N-terminal headpiece bury more hydrophobic residues and are thus more stable. Moreover, in the pathogenic Htt-ex1 dimers the proline-rich region interacts with the polyQ region, which slows the formation of β-sheets.
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Affiliation(s)
- Mohammed Khaled
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany
| | - Birgit Strodel
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany
- Institute of Theoretical and Computational Chemistry, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
- *Correspondence: Birgit Strodel, ; Abdallah Sayyed-Ahmad,
| | - Abdallah Sayyed-Ahmad
- Department of Physics, Birzeit University, Birzeit, Palestine
- *Correspondence: Birgit Strodel, ; Abdallah Sayyed-Ahmad,
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7
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Matlahov I, Boatz JC, C.A. van der Wel P. Selective observation of semi-rigid non-core residues in dynamically complex mutant huntingtin protein fibrils. J Struct Biol X 2022; 6:100077. [PMID: 36419510 PMCID: PMC9677204 DOI: 10.1016/j.yjsbx.2022.100077] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 09/20/2022] [Accepted: 11/07/2022] [Indexed: 11/13/2022] Open
Abstract
Mutant huntingtin exon 1 fibrils feature a broad range of molecular dynamics. Molecular motion is coupled to water dynamics outside the fiber core. Dynamics-based spectral editing ssNMR reveals mobile non-core residues. Intermediate-motion selection via dipolar dephasing of rigid sites. Semi-mobile glutamines outside the fiber core observed and identified.
Many amyloid-forming proteins, which are normally intrinsically disordered, undergo a disorder-to-order transition to form fibrils with a rigid β-sheet core flanked by disordered domains. Solid-state NMR (ssNMR) and cryogenic electron microscopy (cryoEM) excel at resolving the rigid structures within amyloid cores but studying the dynamically disordered domains remains challenging. This challenge is exemplified by mutant huntingtin exon 1 (HttEx1), which self-assembles into pathogenic neuronal inclusions in Huntington disease (HD). The mutant protein’s expanded polyglutamine (polyQ) segment forms a fibril core that is rigid and sequestered from the solvent. Beyond the core, solvent-exposed surface residues mediate biological interactions and other properties of fibril polymorphs. Here we deploy magic angle spinning ssNMR experiments to probe for semi-rigid residues proximal to the fibril core and examine how solvent dynamics impact the fibrils’ segmental dynamics. Dynamic spectral editing (DYSE) 2D ssNMR based on a combination of cross-polarization (CP) ssNMR with selective dipolar dephasing reveals the weak signals of solvent-mobilized glutamine residues, while suppressing the normally strong background of rigid core signals. This type of ‘intermediate motion selection’ (IMS) experiment based on cross-polarization (CP) ssNMR, is complementary to INEPT- and CP-based measurements that highlight highly flexible or highly rigid protein segments, respectively. Integration of the IMS-DYSE element in standard CP-based ssNMR experiments permits the observation of semi-rigid residues in a variety of contexts, including in membrane proteins and protein complexes. We discuss the relevance of semi-rigid solvent-facing residues outside the fibril core to the latter’s detection with specific dyes and positron emission tomography tracers.
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Zhang Y, Liu Y, Zhao W, Sun Y. Hydroxylated single-walled carbon nanotube inhibits β2m 21-31 fibrillization and disrupts pre-formed proto-fibrils. Int J Biol Macromol 2021; 193:1-7. [PMID: 34687758 DOI: 10.1016/j.ijbiomac.2021.10.103] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Revised: 10/11/2021] [Accepted: 10/14/2021] [Indexed: 11/17/2022]
Abstract
Pathological aggregation of amyloid polypeptides is associated with numerous degenerative diseases. Preventing aggregation and clearing amyloid deposits are considered as promising strategies against amyloidosis. With the capacity of crossing the blood-brain barrier and good biocompatibility, the hydroxylated single-walled carbon nanotube (SWCNT-OH) has been shown with excellent anti-amyloid properties. Here, we systematically studied the SWCNT-OH effects on the fibrillization of the β2m21-31 peptides utilizing all-atom discrete molecular dynamics (DMD) simulation. Our results demonstrated the isolated β2m21-31 peptides first nucleated into unstructured oligomers followed by coil-to-sheet conformational conversions in oligomers with at least six peptides. The elongation and lateral surfaces of the preformed β-sheet could catalyze the other unstructured monomers and small oligomers converted into β-sheet formations via dock-lock fibril growth and secondary nucleation processes. Eventually, the β2m21-31 peptides would self-assemble into well-ordered cross-β structures. Regardless of isolated monomers or well-defined cross-β assemblies, the β2m21-31 would attach on the surfaces of SWCNT-OH adopting unstructured formations indicating the SWCNT-OH not only inhibited the fibrillization of β2m21-31 but also destroyed pre-formed proto-fibrils. Overall, our study displays a complete picture of the fibrillization mechanism of β2m21-31 and the amyloid inhibitory mechanism of SWCNT-OH, offering new insight into the de-novo design of anti-amyloid inhibitors.
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Affiliation(s)
- Yu Zhang
- School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
| | - Yuying Liu
- School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
| | - Wenhui Zhao
- School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
| | - Yunxiang Sun
- School of Physical Science and Technology, Ningbo University, Ningbo 315211, China.
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9
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Belwal VK, Vijayakumar A, Chaudhary N. Inhibition of huntingtin aggregation by its N-terminal 17-residue peptide and its analogs. Arch Biochem Biophys 2021; 712:109033. [PMID: 34534539 DOI: 10.1016/j.abb.2021.109033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 08/30/2021] [Accepted: 09/13/2021] [Indexed: 10/20/2022]
Abstract
The N-terminal 17-residue stretch of huntingtin (httN17) folds into an amphipathic α-helix. The httN17-harboring polyQ peptides form oligomers that are mediated via the assembly of the httN17 α-helices. The oligomerization results in higher local concentration of the polyglutamine (polyQ) region, thereby facilitating amyloid formation. The httN17 co-assembles with the httN17-harbouring polyQ peptides, thereby reducing the local polyQ concentration, and consequently inhibiting aggregation. This study presents the aggregation inhibition of the exon I region of pathogenic huntingtin by httN17 and its analogs. The C-terminal amidation of httN17 is found to be essential for activity. The httN17 peptides with free amino terminus and the acetylated amino terminus possess comparable activity. The httN17 analog, wherein the Leu7 and Ala10 are substituted with 2-aminoisobutyric acid residues, exhibits significantly higher activity than the native httN17.
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Affiliation(s)
- Vinay Kumar Belwal
- Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, 781 039, India
| | - Aishwarya Vijayakumar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, 781 039, India
| | - Nitin Chaudhary
- Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, 781 039, India.
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10
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Vieweg S, Mahul-Mellier AL, Ruggeri FS, Riguet N, DeGuire SM, Chiki A, Cendrowska U, Dietler G, Lashuel HA. The Nt17 Domain and its Helical Conformation Regulate the Aggregation, Cellular Properties and Neurotoxicity of Mutant Huntingtin Exon 1. J Mol Biol 2021; 433:167222. [PMID: 34492254 DOI: 10.1016/j.jmb.2021.167222] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Revised: 08/25/2021] [Accepted: 08/26/2021] [Indexed: 11/29/2022]
Abstract
Converging evidence points to the N-terminal domain comprising the first 17 amino acids of the Huntingtin protein (Nt17) as a key regulator of its aggregation, cellular properties and toxicity. In this study, we further investigated the interplay between Nt17 and the polyQ domain repeat length in regulating the aggregation and inclusion formation of exon 1 of the Huntingtin protein (Httex1). In addition, we investigated the effect of removing Nt17 or modulating its local structure on the membrane interactions, neuronal uptake, and toxicity of monomeric or fibrillar Httex1. Our results show that the polyQ and Nt17 domains synergistically modulate the aggregation propensity of Httex1 and that the Nt17 domain plays important roles in shaping the surface properties of mutant Httex1 fibrils and regulating their poly-Q-dependent growth, lateral association and neuronal uptake. Removal of Nt17 or disruption of its transient helical conformations slowed the aggregation of monomeric Httex1 in vitro, reduced inclusion formation in cells, enhanced the neuronal uptake and nuclear accumulation of monomeric Httex1 proteins, and was sufficient to prevent cell death induced by Httex1 72Q overexpression. Finally, we demonstrate that the uptake of Httex1 fibrils into primary neurons and the resulting toxicity are strongly influenced by mutations and phosphorylation events that influence the local helical propensity of Nt17. Altogether, our results demonstrate that the Nt17 domain serves as one of the key master regulators of Htt aggregation, internalization, and toxicity and represents an attractive target for inhibiting Htt aggregate formation, inclusion formation, and neuronal toxicity.
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Affiliation(s)
- Sophie Vieweg
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Anne-Laure Mahul-Mellier
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Francesco S Ruggeri
- Laboratory of the Physics of Living Matter, EPFL, 1015 Lausanne, Switzerland
| | - Nathan Riguet
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Sean M DeGuire
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Anass Chiki
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Urszula Cendrowska
- Laboratory of the Physics of Living Matter, EPFL, 1015 Lausanne, Switzerland
| | - Giovanni Dietler
- Laboratory of the Physics of Living Matter, EPFL, 1015 Lausanne, Switzerland
| | - Hilal A Lashuel
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland.
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11
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Pigazzini ML, Lawrenz M, Margineanu A, Kaminski Schierle GS, Kirstein J. An Expanded Polyproline Domain Maintains Mutant Huntingtin Soluble in vivo and During Aging. Front Mol Neurosci 2021; 14:721749. [PMID: 34720872 PMCID: PMC8554126 DOI: 10.3389/fnmol.2021.721749] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Accepted: 08/30/2021] [Indexed: 02/02/2023] Open
Abstract
Huntington's disease is a dominantly inherited neurodegenerative disorder caused by the expansion of a CAG repeat, encoding for the amino acid glutamine (Q), present in the first exon of the protein huntingtin. Over the threshold of Q39 HTT exon 1 (HTTEx1) tends to misfold and aggregate into large intracellular structures, but whether these end-stage aggregates or their on-pathway intermediates are responsible for cytotoxicity is still debated. HTTEx1 can be separated into three domains: an N-terminal 17 amino acid region, the polyglutamine (polyQ) expansion and a C-terminal proline rich domain (PRD). Alongside the expanded polyQ, these flanking domains influence the aggregation propensity of HTTEx1: with the N17 initiating and promoting aggregation, and the PRD modulating it. In this study we focus on the first 11 amino acids of the PRD, a stretch of pure prolines, which are an evolutionary recent addition to the expanding polyQ region. We hypothesize that this proline region is expanding alongside the polyQ to counteract its ability to misfold and cause toxicity, and that expanding this proline region would be overall beneficial. We generated HTTEx1 mutants lacking both flanking domains singularly, missing the first 11 prolines of the PRD, or with this stretch of prolines expanded. We then followed their aggregation landscape in vitro with a battery of biochemical assays, and in vivo in novel models of C. elegans expressing the HTTEx1 mutants pan-neuronally. Employing fluorescence lifetime imaging we could observe the aggregation propensity of all HTTEx1 mutants during aging and correlate this with toxicity via various phenotypic assays. We found that the presence of an expanded proline stretch is beneficial in maintaining HTTEx1 soluble over time, regardless of polyQ length. However, the expanded prolines were only advantageous in promoting the survival and fitness of an organism carrying a pathogenic stretch of Q48 but were extremely deleterious to the nematode expressing a physiological stretch of Q23. Our results reveal the unique importance of the prolines which have and still are evolving alongside expanding glutamines to promote the function of HTTEx1 and avoid pathology.
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Affiliation(s)
- Maria Lucia Pigazzini
- Department of Molecular Physiology and Cell Biology, Leibniz Research Institute for Molecular Pharmacology in the Forschungsverbund Berlin e.V. (FMP), Berlin, Germany
- NeuroCure Cluster of Excellence, Charité Universitätsmedizin Berlin, Berlin, Germany
| | - Mandy Lawrenz
- Department of Molecular Physiology and Cell Biology, Leibniz Research Institute for Molecular Pharmacology in the Forschungsverbund Berlin e.V. (FMP), Berlin, Germany
| | - Anca Margineanu
- Advanced Light Microscopy, Max-Delbrück Centrum for Molecular Medicine (MDC), Berlin, Germany
| | - Gabriele S. Kaminski Schierle
- Molecular Neuroscience Group, Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, United Kingdom
| | - Janine Kirstein
- Department of Molecular Physiology and Cell Biology, Leibniz Research Institute for Molecular Pharmacology in the Forschungsverbund Berlin e.V. (FMP), Berlin, Germany
- Department of Cell Biology, University of Bremen, Bremen, Germany
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12
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Chongtham A, Isas JM, Pandey NK, Rawat A, Yoo JH, Mastro T, Kennedy MB, Langen R, Khoshnan A. Amplification of neurotoxic HTTex1 assemblies in human neurons. Neurobiol Dis 2021; 159:105517. [PMID: 34563643 DOI: 10.1016/j.nbd.2021.105517] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 08/24/2021] [Accepted: 09/21/2021] [Indexed: 11/25/2022] Open
Abstract
Huntington's disease (HD) is a genetically inherited neurodegenerative disorder caused by expansion of a polyglutamine (polyQ) repeat in the exon-1 of huntingtin protein (HTT). The expanded polyQ enhances the amyloidogenic propensity of HTT exon 1 (HTTex1), which forms a heterogeneous mixture of assemblies with a broad neurotoxicity spectrum. While predominantly intracellular, monomeric and aggregated mutant HTT species are also present in the cerebrospinal fluids of HD patients, however, their biological properties are not well understood. To explore the role of extracellular mutant HTT in aggregation and toxicity, we investigated the uptake and amplification of recombinant HTTex1 assemblies in cell culture models. We find that small HTTex1 fibrils preferentially enter human neurons and trigger the amplification of neurotoxic assemblies; astrocytes or epithelial cells are not permissive. The amplification of HTTex1 in neurons depletes endogenous HTT protein with non-pathogenic polyQ repeat, activates apoptotic caspase-3 pathway and induces nuclear fragmentation. Using a panel of novel monoclonal antibodies and genetic mutation, we identified epitopes within the N-terminal 17 amino acids and proline-rich domain of HTTex1 to be critical in neural uptake and amplification. Synaptosome preparations from the brain homogenates of HD mice also contain mutant HTT species, which enter neurons and behave similar to small recombinant HTTex1 fibrils. These studies suggest that amyloidogenic extracellular mutant HTTex1 assemblies may preferentially enter neurons, propagate and promote neurodegeneration.
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Affiliation(s)
| | - J Mario Isas
- Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, CA 90089, USA
| | - Nitin K Pandey
- Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, CA 90089, USA
| | - Anoop Rawat
- Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, CA 90089, USA
| | - Jung Hyun Yoo
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA
| | - Tara Mastro
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA
| | - Mary B Kennedy
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA
| | - Ralf Langen
- Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, CA 90089, USA
| | - Ali Khoshnan
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA.
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13
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Mario Isas J, Pandey NK, Xu H, Teranishi K, Okada AK, Fultz EK, Rawat A, Applebaum A, Meier F, Chen J, Langen R, Siemer AB. Huntingtin fibrils with different toxicity, structure, and seeding potential can be interconverted. Nat Commun 2021; 12:4272. [PMID: 34257293 PMCID: PMC8277859 DOI: 10.1038/s41467-021-24411-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Accepted: 06/17/2021] [Indexed: 11/09/2022] Open
Abstract
The first exon of the huntingtin protein (HTTex1) important in Huntington's disease (HD) can form cross-β fibrils of varying toxicity. We find that the difference between these fibrils is the degree of entanglement and dynamics of the C-terminal proline-rich domain (PRD) in a mechanism analogous to polyproline film formation. In contrast to fibril strains found for other cross-β fibrils, these HTTex1 fibril types can be interconverted. This is because the structure of their polyQ fibril core remains unchanged. Further, we find that more toxic fibrils of low entanglement have higher affinities for protein interactors and are more effective seeds for recombinant HTTex1 and HTTex1 in cells. Together these data show how the structure of a framing sequence at the surface of a fibril can modulate seeding, protein-protein interactions, and thereby toxicity in neurodegenerative disease.
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Affiliation(s)
- J Mario Isas
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Nitin K Pandey
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Hui Xu
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Kazuki Teranishi
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Alan K Okada
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.,Department of Emergency Medicine, Regions Hospital, St. Paul, MN, USA
| | - Ellisa K Fultz
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Anoop Rawat
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Anise Applebaum
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Franziska Meier
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Jeannie Chen
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Ralf Langen
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
| | - Ansgar B Siemer
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
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14
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Cryo-electron tomography provides topological insights into mutant huntingtin exon 1 and polyQ aggregates. Commun Biol 2021; 4:849. [PMID: 34239038 PMCID: PMC8266869 DOI: 10.1038/s42003-021-02360-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 06/15/2021] [Indexed: 01/27/2023] Open
Abstract
Huntington disease (HD) is a neurodegenerative trinucleotide repeat disorder caused by an expanded poly-glutamine (polyQ) tract in the mutant huntingtin (mHTT) protein. The formation and topology of filamentous mHTT inclusions in the brain (hallmarks of HD implicated in neurotoxicity) remain elusive. Using cryo-electron tomography and subtomogram averaging, here we show that mHTT exon 1 and polyQ-only aggregates in vitro are structurally heterogenous and filamentous, similar to prior observations with other methods. Yet, we find filaments in both types of aggregates under ~2 nm in width, thinner than previously reported, and regions forming large sheets. In addition, our data show a prevalent subpopulation of filaments exhibiting a lumpy slab morphology in both aggregates, supportive of the polyQ core model. This provides a basis for future cryoET studies of various aggregated mHTT and polyQ constructs to improve their structure-based modeling as well as their identification in cells without fusion tags.
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15
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Ashami K, Falk AS, Hurd C, Garg S, Cervantes SA, Rawat A, Siemer AB. Droplet and fibril formation of the functional amyloid Orb2. J Biol Chem 2021; 297:100804. [PMID: 34044018 PMCID: PMC8294575 DOI: 10.1016/j.jbc.2021.100804] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 05/10/2021] [Accepted: 05/18/2021] [Indexed: 01/18/2023] Open
Abstract
The functional amyloid Orb2 belongs to the cytoplasmic polyadenylation element binding (CPEB) protein family and plays an important role in long-term memory formation in Drosophila. The Orb2 domain structure combines RNA recognition motifs with low-complexity sequences similar to many RNA-binding proteins shown to form protein droplets via liquid–liquid phase separation (LLPS) in vivo and in vitro. This similarity suggests that Orb2 might also undergo LLPS. However, cellular Orb2 puncta have very little internal protein mobility, and Orb2 forms fibrils in Drosophila brains that are functionally active indicating that LLPS might not play a role for Orb2. In the present work, we reconcile these two views on Orb2 droplet formation. Using fluorescence microscopy, we show that soluble Orb2 can indeed phase separate into protein droplets. However, fluorescence recovery after photobleaching (FRAP) data shows that these droplets have either no or only an extremely short-lived liquid phase and appear maturated right after formation. Orb2 fragments that lack the C-terminal RNA-binding domain (RBD) form fibrils out of these droplets. Solid-state NMR shows that these fibrils have well-ordered static domains in addition to the Gln/His-rich fibril core. Further, we find that full-length Orb2B, which is by far the major component of Orb2 fibrils in vivo, does not transition into fibrils but remains in the droplet phase. Together, our data suggest that phase separation might play a role in initiating the formation of functional Orb2 fibrils.
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Affiliation(s)
- Kidist Ashami
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Alexander S Falk
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Connor Hurd
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Samridhi Garg
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Silvia A Cervantes
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Anoop Rawat
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Ansgar B Siemer
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
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16
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Liu EN, Park G, Nohara J, Guo Z. Effect of spin labelling on the aggregation kinetics of yeast prion protein Ure2. ROYAL SOCIETY OPEN SCIENCE 2021; 8:201747. [PMID: 33959337 PMCID: PMC8074925 DOI: 10.1098/rsos.201747] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 02/10/2021] [Indexed: 06/12/2023]
Abstract
Amyloid formation is involved in a wide range of neurodegenerative diseases including Alzheimer's and prion diseases. Structural understanding of the amyloid is critical to delineate the mechanism of aggregation and its pathological spreading. Site-directed spin labelling has emerged as a powerful structural tool in the studies of amyloid structures and provided structural evidence for the parallel in-register β-sheet structure for a wide range of amyloid proteins. It is generally accepted that spin labelling does not disrupt the structure of the amyloid fibrils, the end product of protein aggregation. The effect on the rate of protein aggregation, however, has not been well characterized. Here, we employed a scanning mutagenesis approach to study the effect of spin labelling on the aggregation rate of 79 spin-labelled variants of the Ure2 prion domain. The aggregation of Ure2 protein is the basis of yeast prion [URE3]. We found that all spin-labelled Ure2 mutants aggregated within the experimental timeframe of 15 to 40 h. Among the 79 spin-labelled positions, only five residue sites (N23, N27, S33, I35 and G42) showed a dramatic delay in the aggregation rate as a result of spin labelling. These positions may be important for fibril nucleation, a rate-limiting step in aggregation. Importantly, spin labelling at most of the sites had a muted effect on Ure2 aggregation kinetics, showing a general tolerance of spin labelling in protein aggregation studies.
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Affiliation(s)
- Emilie N. Liu
- Department of Neurology, Brain Research Institute, Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA
| | - Giovanna Park
- Department of Neurology, Brain Research Institute, Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA
| | - Junsuke Nohara
- Department of Neurology, Brain Research Institute, Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA
| | - Zhefeng Guo
- Department of Neurology, Brain Research Institute, Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA
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17
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Falk AS, Bravo-Arredondo JM, Varkey J, Pacheco S, Langen R, Siemer AB. Structural Model of the Proline-Rich Domain of Huntingtin Exon-1 Fibrils. Biophys J 2020; 119:2019-2028. [PMID: 33096080 PMCID: PMC7732765 DOI: 10.1016/j.bpj.2020.10.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Revised: 08/17/2020] [Accepted: 10/13/2020] [Indexed: 01/09/2023] Open
Abstract
Huntington's disease is a heritable neurodegenerative disease that is caused by a CAG expansion in the first exon of the huntingtin gene. This expansion results in an elongated polyglutamine domain that increases the propensity of huntingtin exon-1 to form cross-β fibrils. Although the polyglutamine domain is important for fibril formation, the dynamic, C-terminal proline-rich domain (PRD) of huntingtin exon-1 makes up a large fraction of the fibril surface. Because potential fibril toxicity has to be mediated by interactions of the fibril surface with its cellular environment, we wanted to model the conformational space adopted by the PRD. We ran 800-ns long molecular dynamics simulations of the PRD using an explicit water model optimized for intrinsically disordered proteins. These simulations accurately predicted our previous solid-state NMR data and newly acquired electron paramagnetic resonance double electron-electron resonance distances, lending confidence in their accuracy. The simulations show that the PRD generally forms an imperfect polyproline (polyP) II helical conformation. The two polyP regions within the PRD stay in a polyP II helix for most of the simulation, whereas occasional kinks in the proline-rich linker region cause an overall bend in the PRD structure. The dihedral angles of the glycine at the end of the second polyP region are very variable, effectively decoupling the highly dynamic 12 C-terminal residues from the rest of the PRD.
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Affiliation(s)
- Alexander S Falk
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, California
| | - José M Bravo-Arredondo
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, California
| | - Jobin Varkey
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, California
| | - Sayuri Pacheco
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, California
| | - Ralf Langen
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, California
| | - Ansgar B Siemer
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, California.
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18
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Implications of the Orb2 Amyloid Structure in Huntington's Disease. Int J Mol Sci 2020; 21:ijms21186910. [PMID: 32967102 PMCID: PMC7555547 DOI: 10.3390/ijms21186910] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 09/11/2020] [Accepted: 09/16/2020] [Indexed: 02/06/2023] Open
Abstract
Huntington’s disease is a progressive, autosomal dominant, neurodegenerative disorder caused by an expanded CAG repeat in the huntingtin gene. As a result, the translated protein, huntingtin, contains an abnormally long polyglutamine stretch that makes it prone to misfold and aggregating. Aggregation of huntingtin is believed to be the cause of Huntington’s disease. However, understanding on how, and why, huntingtin aggregates are deleterious has been hampered by lack of enough relevant structural data. In this review, we discuss our recent findings on a glutamine-based functional amyloid isolated from Drosophila brain and how this information provides plausible structural insight on the structure of huntingtin deposits in the brain.
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19
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Lo CH, Pandey NK, Lim CKW, Ding Z, Tao M, Thomas DD, Langen R, Sachs JN. Discovery of Small Molecule Inhibitors of Huntingtin Exon 1 Aggregation by FRET-Based High-Throughput Screening in Living Cells. ACS Chem Neurosci 2020; 11:2286-2295. [PMID: 32568514 DOI: 10.1021/acschemneuro.0c00226] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Huntington's disease (HD) is the most common inherited neurodegenerative disorder and one of the nine polyglutamine (polyQ) diseases. HD is characterized by the pathological aggregation of the misfolded huntingtin exon 1 protein (Httex1) with abnormally long polyQ expansion due to genetic mutation. While there is currently no effective treatment for HD, inhibition of aggregate formation represents a direct approach in mediating the toxicity associated with Httex1 misfolding. To exploit this therapeutic window, we engineered two fluorescence resonance energy transfer (FRET) based biosensors that monitor the aggregation of Httex1 with different expanded Q-lengths (Q39 and Q72) in living cells. These FRET biosensors, together with a high-precision fluorescence lifetime detection platform, enable high-throughput screening of small molecules that target Httex1 aggregation. We found six small molecules that decreased the FRET of the biosensors and reduced Httex1-Q72-induced neuronal cytotoxicity in N2a cells with nanomolar potency. Using advanced SPR and EPR techniques, we confirmed that the compounds directly bind to Httex1 fibrils and inhibit aggregate formation. This strategy in targeting the Httex1 aggregates can be applicable to other proteins involved in polyQ related diseases.
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Affiliation(s)
- Chih Hung Lo
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Nitin K. Pandey
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
| | - Colin Kin-Wye Lim
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Zhipeng Ding
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Meixin Tao
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
| | - David D. Thomas
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, United States
- Photonic Pharma LLC, Minneapolis, Minnesota 55410, United States
| | - Ralf Langen
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
| | - Jonathan N. Sachs
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
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20
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Hegde RN, Chiki A, Petricca L, Martufi P, Arbez N, Mouchiroud L, Auwerx J, Landles C, Bates GP, Singh-Bains MK, Dragunow M, Curtis MA, Faull RL, Ross CA, Caricasole A, Lashuel HA. TBK1 phosphorylates mutant Huntingtin and suppresses its aggregation and toxicity in Huntington's disease models. EMBO J 2020; 39:e104671. [PMID: 32757223 PMCID: PMC7459410 DOI: 10.15252/embj.2020104671] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 06/09/2020] [Accepted: 06/16/2020] [Indexed: 12/17/2022] Open
Abstract
Phosphorylation of the N‐terminal domain of the huntingtin (HTT) protein has emerged as an important regulator of its localization, structure, aggregation, clearance and toxicity. However, validation of the effect of bona fide phosphorylation in vivo and assessing the therapeutic potential of targeting phosphorylation for the treatment of Huntington's disease (HD) require the identification of the enzymes that regulate HTT phosphorylation. Herein, we report the discovery and validation of a kinase, TANK‐binding kinase 1 (TBK1), that efficiently phosphorylates full‐length and N‐terminal HTT fragments in vitro (at S13/S16), in cells (at S13) and in vivo. TBK1 expression in HD models (cells, primary neurons, and Caenorhabditis elegans) increases mutant HTT exon 1 phosphorylation and reduces its aggregation and cytotoxicity. We demonstrate that the TBK1‐mediated neuroprotective effects are due to phosphorylation‐dependent inhibition of mutant HTT exon 1 aggregation and an increase in autophagic clearance of mutant HTT. These findings suggest that upregulation and/or activation of TBK1 represents a viable strategy for the treatment of HD by simultaneously lowering mutant HTT levels and blocking its aggregation.
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Affiliation(s)
- Ramanath Narayana Hegde
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Anass Chiki
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Lara Petricca
- Department of Neuroscience, IRBM Science Park, Rome, Italy
| | - Paola Martufi
- Department of Neuroscience, IRBM Science Park, Rome, Italy
| | - Nicolas Arbez
- Division of Neurobiology, Department of Psychiatry and Departments of Neurology, Neuroscience and Pharmacology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Laurent Mouchiroud
- Laboratory of Integrative and Systems Physiology, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Johan Auwerx
- Laboratory of Integrative and Systems Physiology, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Christian Landles
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London, UK
| | - Gillian P Bates
- Huntington's Disease Centre, Department of Neurodegenerative Disease and UK Dementia Research Institute at UCL, Queen Square Institute of Neurology, University College London, London, UK
| | - Malvindar K Singh-Bains
- Centre for Brain Research, Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
| | - Mike Dragunow
- Centre for Brain Research, Department of Pharmacology and Clinical Pharmacology, University of Auckland, Auckland, New Zealand
| | - Maurice A Curtis
- Centre for Brain Research, Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
| | - Richard Lm Faull
- Centre for Brain Research, Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
| | - Christopher A Ross
- Division of Neurobiology, Department of Psychiatry and Departments of Neurology, Neuroscience and Pharmacology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | | | - Hilal A Lashuel
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
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21
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Belwal VK, Datta D, Chaudhary N. The β‐turn‐supporting motif in the polyglutamine binding peptide QBP1 is essential for inhibiting huntingtin aggregation. FEBS Lett 2020; 594:2894-2903. [DOI: 10.1002/1873-3468.13873] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Revised: 06/05/2020] [Accepted: 06/17/2020] [Indexed: 11/11/2022]
Affiliation(s)
- Vinay Kumar Belwal
- Department of Biosciences and Bioengineering Indian Institute of Technology Guwahati India
| | - Debika Datta
- Department of Biosciences and Bioengineering Indian Institute of Technology Guwahati India
| | - Nitin Chaudhary
- Department of Biosciences and Bioengineering Indian Institute of Technology Guwahati India
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22
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Boatz JC, Piretra T, Lasorsa A, Matlahov I, Conway JF, van der Wel PCA. Protofilament Structure and Supramolecular Polymorphism of Aggregated Mutant Huntingtin Exon 1. J Mol Biol 2020; 432:4722-4744. [PMID: 32598938 DOI: 10.1016/j.jmb.2020.06.021] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2020] [Revised: 06/01/2020] [Accepted: 06/18/2020] [Indexed: 12/11/2022]
Abstract
Huntington's disease is a progressive neurodegenerative disease caused by expansion of the polyglutamine domain in the first exon of huntingtin (HttEx1). The extent of expansion correlates with disease progression and formation of amyloid-like protein deposits within the brain. The latter display polymorphism at the microscopic level, both in cerebral tissue and in vitro. Such polymorphism can dramatically influence cytotoxicity, leading to much interest in the conditions and mechanisms that dictate the formation of polymorphs. We examine conditions that govern HttEx1 polymorphism in vitro, including concentration and the role of the non-polyglutamine flanking domains. Using electron microscopy, we observe polymorphs that differ in width and tendency for higher-order bundling. Strikingly, aggregation yields different polymorphs at low and high concentrations. Narrow filaments dominate at low concentrations that may be more relevant in vivo. We dissect the role of N- and C-terminal flanking domains using protein with the former (httNT or N17) largely removed. The truncated protein is generated by trypsin cleavage of soluble HttEx1 fusion protein, which we analyze in some detail. Dye binding and solid-state NMR studies reveal changes in fibril surface characteristics and flanking domain mobility. Higher-order interactions appear facilitated by the C-terminal tail, while the polyglutamine forms an amyloid core resembling those of other polyglutamine deposits. Fibril-surface-mediated branching, previously attributed to secondary nucleation, is reduced in absence of httNT. A new model for the architecture of the HttEx1 filaments is presented and discussed in context of the assembly mechanism and biological activity.
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Affiliation(s)
- Jennifer C Boatz
- Department of Structural Biology, School of Medicine, University of Pittsburgh, 3501 5th Ave, Biomedical Science Tower 3, Pittsburgh, PA 15213, USA.
| | - Talia Piretra
- Department of Structural Biology, School of Medicine, University of Pittsburgh, 3501 5th Ave, Biomedical Science Tower 3, Pittsburgh, PA 15213, USA.
| | - Alessia Lasorsa
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747, AG, Groningen, the Netherlands.
| | - Irina Matlahov
- Department of Structural Biology, School of Medicine, University of Pittsburgh, 3501 5th Ave, Biomedical Science Tower 3, Pittsburgh, PA 15213, USA; Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747, AG, Groningen, the Netherlands.
| | - James F Conway
- Department of Structural Biology, School of Medicine, University of Pittsburgh, 3501 5th Ave, Biomedical Science Tower 3, Pittsburgh, PA 15213, USA.
| | - Patrick C A van der Wel
- Department of Structural Biology, School of Medicine, University of Pittsburgh, 3501 5th Ave, Biomedical Science Tower 3, Pittsburgh, PA 15213, USA; Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747, AG, Groningen, the Netherlands.
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23
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Siemer AB. Advances in studying protein disorder with solid-state NMR. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2020; 106:101643. [PMID: 31972419 PMCID: PMC7202078 DOI: 10.1016/j.ssnmr.2020.101643] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 01/06/2020] [Accepted: 01/07/2020] [Indexed: 05/26/2023]
Abstract
Solution NMR is a key tool to study intrinsically disordered proteins (IDPs), whose importance for biological function is widely accepted. However, disordered proteins are not limited to solution and are also found in non-soluble systems such as fibrils and membrane proteins. In this Trends article, I will discuss how solid-state NMR can be used to study disorder in non-soluble proteins. Techniques based on dipolar couplings can study static protein disorder which either occurs naturally as e.g. in spider silk or can be induced by freeze trapping IDPs or unfolded proteins. In this case, structural ensembles are directly reflected by a static distribution of dihedral angels that can be determined by the distribution of chemical shifts or other methods. Techniques based on J-couplings can detect dynamic protein disorder under MAS. In this case, only average chemical shifts are measured but disorder can be characterized with a variety of data including secondary chemical shifts, relaxation rates, paramagnetic relaxation enhancements, or residual dipolar couplings. I describe both technical aspects and examples of solid-state NMR on protein disorder and end the article with a discussion of challenges and opportunities of this emerging field.
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Affiliation(s)
- Ansgar B Siemer
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Univeristy of Southern California, 1501 San Pablo Street, Los Angeles, CA, 90033, USA.
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24
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Doherty CPA, Ulamec SM, Maya-Martinez R, Good SC, Makepeace J, Khan GN, van Oosten-Hawle P, Radford SE, Brockwell DJ. A short motif in the N-terminal region of α-synuclein is critical for both aggregation and function. Nat Struct Mol Biol 2020; 27:249-259. [PMID: 32157247 PMCID: PMC7100612 DOI: 10.1038/s41594-020-0384-x] [Citation(s) in RCA: 92] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Accepted: 01/22/2020] [Indexed: 02/04/2023]
Abstract
Aggregation of human α-synuclein (αSyn) is linked to Parkinson’s disease (PD) pathology. The central region of the αSyn sequence contains the non-amyloid β-component (NAC) crucial for aggregation. However, how NAC flanking regions modulate αSyn aggregation remains unclear. Using bioinformatics, mutation, and NMR we identify a 7-residue sequence, named P1 (residues 36-42), that controls αSyn aggregation. Deletion or substitution of this ‘master-controller’ prevents aggregation at pH 7.5 in vitro. At lower pH, P1 synergises with a sequence containing the PreNAC region (P2, residues 45-57) to prevent aggregation. Deleting P1 (ΔP1) or both P1 and P2 (ΔΔ) also prevents age-dependent αSyn aggregation and toxicity in C. elegans models and prevents αSyn-mediated vesicle fusion by altering the conformational properties of the protein when lipid-bound. The results highlight the importance of a master-controller sequence motif that controls both αSyn aggregation and function- a region that could be targeted to prevent aggregation in disease.
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Affiliation(s)
- Ciaran P A Doherty
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Sabine M Ulamec
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Roberto Maya-Martinez
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Sarah C Good
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Jemma Makepeace
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - G Nasir Khan
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Patricija van Oosten-Hawle
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Sheena E Radford
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom.
| | - David J Brockwell
- Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom.
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25
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Moldovean SN, Chiş V. Molecular Dynamics Simulations Applied to Structural and Dynamical Transitions of the Huntingtin Protein: A Review. ACS Chem Neurosci 2020; 11:105-120. [PMID: 31841621 DOI: 10.1021/acschemneuro.9b00561] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Over the recent years, Huntington's disease (HD) has become widely discussed in the scientific literature especially because at the mutant level there are several contradictions regarding the aggregation mechanism. The specific role of the physiological huntingtin protein remains unknown, due to the lack of characterization of its entire crystallographic structure, making the experimental and theoretical research even harder when taking into consideration its involvement in multiple biological functions and its high affinity for different interacting partners. Different types of models, containing fewer (not more than 35 Qs) polyglutamine residues for the WT structure and above 35 Qs for the mutants, were subjected to classical or advanced MD simulations to establish the proteins' structural stability by evaluating their conformational changes. Outside the polyQ tract, there are two other regions of interest (the N17 domain and the polyP rich domain) considered to be essential for the aggregation kinetics at the mutant level. The polymerization process is considered to be dependent on the polyQ length. As the polyQ tract's dimension increases, the structures present more β-sheet conformations. Contrarily, it is also considered that the aggregation stability is not necessarily dependent on the number of Qs, while the initial stage of the aggregation seed might play the decisive role. A general assumption regarding the polyP domain is that it might preserve the polyQ structures soluble by acting as an antagonist for β-sheet formation.
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Affiliation(s)
| | - Vasile Chiş
- Babeş-Bolyai University, Faculty of Physics, Kogălniceanu 1, RO-400084 Cluj-Napoca, Romania
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26
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Ko J, Isas JM, Sabbaugh A, Yoo JH, Pandey NK, Chongtham A, Ladinsky M, Wu WL, Rohweder H, Weiss A, Macdonald D, Munoz-Sanjuan I, Langen R, Patterson PH, Khoshnan A. Identification of distinct conformations associated with monomers and fibril assemblies of mutant huntingtin. Hum Mol Genet 2019; 27:2330-2343. [PMID: 29912367 DOI: 10.1093/hmg/ddy141] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Revised: 04/12/2018] [Accepted: 04/16/2018] [Indexed: 11/14/2022] Open
Abstract
The N-terminal fragments of mutant huntingtin (mHTT) misfold and assemble into oligomers, which ultimately bundle into insoluble fibrils. Conformations unique to various assemblies of mHTT remain unknown. Knowledge on the half-life of various multimeric structures of mHTT is also scarce. Using a panel of four new antibodies named PHP1-4, we have identified new conformations in monomers and assembled structures of mHTT. PHP1 and PHP2 bind to epitopes within the proline-rich domain (PRD), whereas PHP3 and PHP4 interact with motifs formed at the junction of polyglutamine (polyQ) and polyproline (polyP) repeats of HTT. The PHP1- and PHP2-reactive epitopes are exposed in fibrils of mHTT exon1 (mHTTx1) generated from recombinant proteins and mHTT assemblies, which progressively accumulate in the nuclei, cell bodies and neuropils in the brains of HD mouse models. Notably, electron microscopic examination of brain sections of HD mice revealed that PHP1- and PHP2-reactive mHTT assemblies are present in myelin sheath and in vesicle-like structures. Moreover, PHP1 and PHP2 antibodies block seeding and subsequent fibril assembly of mHTTx1 in vitro and in a cell culture model of HD. PHP3 and PHP4 bind to epitopes in full-length and N-terminal fragments of monomeric mHTT and binding diminishes as the mHTTx1 assembles into fibrils. Interestingly, PHP3 and PHP4 also prevent the aggregation of mHTTx1 in vitro highlighting a regulatory function for the polyQ-polyP motifs. These newly detected conformations may affect fibril assembly, stability and intercellular transport of mHTT.
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Affiliation(s)
- Jan Ko
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA
| | - J Mario Isas
- Zilka Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, CA 90089, USA
| | - Adam Sabbaugh
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA
| | - Jung Hyun Yoo
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA
| | - Nitin K Pandey
- Zilka Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, CA 90089, USA
| | | | - Mark Ladinsky
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA
| | - Wei-Li Wu
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA
| | | | - Andreas Weiss
- Evotec, Manfred Eigen Campus, Hamburg 22419, Germany
| | | | | | - Ralf Langen
- Zilka Neurogenetic Institute, Keck School of Medicine of USC, Los Angeles, CA 90089, USA
| | | | - Ali Khoshnan
- Biology and Bioengineering, Caltech, Pasadena, CA 91125, USA
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27
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Tao M, Pandey NK, Barnes R, Han S, Langen R. Structure of Membrane-Bound Huntingtin Exon 1 Reveals Membrane Interaction and Aggregation Mechanisms. Structure 2019; 27:1570-1580.e4. [PMID: 31466833 DOI: 10.1016/j.str.2019.08.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 07/23/2019] [Accepted: 08/09/2019] [Indexed: 02/08/2023]
Abstract
Huntington's disease is caused by a polyQ expansion in the first exon of huntingtin (Httex1). Membrane interaction of huntingtin is of physiological and pathological relevance. Using electron paramagnetic resonance and Overhauser dynamic nuclear polarization, we find that the N-terminal residues 3-13 of wild-type Httex1(Q25) form a membrane-bound, amphipathic α helix. This helix is positioned in the interfacial region, where it is sensitive to membrane curvature and electrostatic interactions with head-group charges. Residues 14-22, which contain the first five residues of the polyQ region, are in a transition region that remains in the interfacial region without taking up a stable, α-helical structure. The remaining C-terminal portion is solvent exposed. The phosphomimetic S13D/S16D mutations, which are known to protect from toxicity, inhibit membrane binding and attenuate membrane-mediated aggregation of mutant Httex1(Q46) due to electrostatic repulsion. Targeting the N-terminal membrane anchor using post-translational modifications or specific binders could be a potential means to reduce aggregation and toxicity in vivo.
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Affiliation(s)
- Meixin Tao
- Department of Neuroscience and Physiology, Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
| | - Nitin K Pandey
- Department of Neuroscience and Physiology, Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
| | - Ryan Barnes
- Department of Chemistry and Biochemistry, Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Songi Han
- Department of Chemistry and Biochemistry, Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Ralf Langen
- Department of Neuroscience and Physiology, Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
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28
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Matlahov I, van der Wel PC. Conformational studies of pathogenic expanded polyglutamine protein deposits from Huntington's disease. Exp Biol Med (Maywood) 2019; 244:1584-1595. [PMID: 31203656 PMCID: PMC6920524 DOI: 10.1177/1535370219856620] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Huntington’s disease, like other neurodegenerative diseases, continues to lack an
effective cure. Current treatments that address early symptoms ultimately fail
Huntington’s disease patients and their families, with the disease typically
being fatal within 10–15 years from onset. Huntington’s disease is an inherited
disorder with motor and mental impairment, and is associated with the genetic
expansion of a CAG codon repeat encoding a polyglutamine-segment-containing
protein called huntingtin. These Huntington’s disease mutations cause misfolding
and aggregation of fragments of the mutant huntingtin protein, thereby likely
contributing to disease toxicity through a combination of gain-of-toxic-function
for the misfolded aggregates and a loss of function from sequestration of
huntingtin and other proteins. As with other amyloid diseases, the mutant
protein forms non-native fibrillar structures, which in Huntington’s disease are
found within patients’ neurons. The intracellular deposits are associated with
dysregulation of vital processes, and inter-neuronal transport of aggregates may
contribute to disease progression. However, a molecular understanding of these
aggregates and their detrimental effects has been frustrated by insufficient
structural data on the misfolded protein state. In this review, we examine
recent developments in the structural biology of polyglutamine-expanded
huntingtin fragments, and especially the contributions enabled by advances in
solid-state nuclear magnetic resonance spectroscopy. We summarize and discuss
our current structural understanding of the huntingtin deposits and how this
information furthers our understanding of the misfolding mechanism and disease
toxicity mechanisms.
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Affiliation(s)
- Irina Matlahov
- Department of Structural Biology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Patrick Ca van der Wel
- Department of Structural Biology, University of Pittsburgh, Pittsburgh, PA 15213, USA.,Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747 AG, The Netherlands
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29
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Priya SB, Gromiha MM. Structural insights into the aggregation mechanism of huntingtin exon 1 protein fragment with different polyQ-lengths. J Cell Biochem 2019; 120:10519-10529. [PMID: 30672003 DOI: 10.1002/jcb.28338] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Accepted: 11/29/2018] [Indexed: 12/19/2022]
Abstract
Huntington disease is a neurodegenerative disorder caused by the expansion of polyglutamine (polyQ) at the N-terminal of the huntingtin exon 1 protein. The detailed structure and the mechanism behind this aggregation remain unclear and it is assumed that the polyQ undergoes a conformational transition to the β-sheet structure when it aggregates. Investigating the misfolding of polyQ facilitates the determination of the molecular mechanism of aggregation and can potentially help in developing a novel approach to inhibit polyQ aggregation. Moreover, the flanking sequences of the polyQ region play a vital role in structural changes and the aggregation mechanism. We performed all-atom molecular dynamics simulations to gain structural insights into the aggregation mechanism using eight different models with glutamine repeat lengths Q27 , Q27 P11 , Q34 , Q35 , Q36 , Q40 , Q50 , and Q50 P11 . In the models without flanking polyPs, we noticed that the transformation of a random coil to β-sheet occurs when the number of Q increases. We also found that the flanking polyPs prevent aggregation by decreasing the probability of forming a β-sheet structure. When polyQ length increases, the 17 N-terminal flanking residues are more likely to adopt a β-sheet conformation from α-helix and coil. From our simulations, we suggest that at least 34 glutamines are required for initiating aggregation and 40 residues length is critical for the aggregation of huntingtin exon 1 protein for disease onset. This study provides structural insights into misfolding and the role of flanking sequences in huntingtin aggregation which will further help in developing therapeutic strategies for Huntington's disease.
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Affiliation(s)
- S Binny Priya
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
| | - M Michael Gromiha
- Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India.,Advanced Computational Drug Discovery Unit (ACDD), Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan
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30
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Bravo-Arredondo JM, Kegulian NC, Schmidt T, Pandey NK, Situ AJ, Ulmer TS, Langen R. The folding equilibrium of huntingtin exon 1 monomer depends on its polyglutamine tract. J Biol Chem 2018; 293:19613-19623. [PMID: 30315108 DOI: 10.1074/jbc.ra118.004808] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 10/05/2018] [Indexed: 11/06/2022] Open
Abstract
Expansion of the polyglutamine (polyQ) tract in exon 1 of the huntingtin protein (Httex1) leads to Huntington's disease resulting in fatal neurodegeneration. However, it remains poorly understood how polyQ expansions alter protein structure and cause toxicity. Using CD, EPR, and NMR spectroscopy, we found here that monomeric Httex1 consists of two co-existing structural states whose ratio is determined by polyQ tract length. We observed that short Q-lengths favor a largely random-coil state, whereas long Q-lengths increase the proportion of a predominantly α-helical state. We also note that by following a mobility gradient, Httex1 α-helical conformation is restricted to the N-terminal N17 region and to the N-terminal portion of the adjoining polyQ tract. Structuring in both regions was interdependent and likely stabilized by tertiary contacts. Although little helicity was present in N17 alone, each Gln residue in Httex1 enhanced helix stability by 0.03-0.05 kcal/mol, causing a pronounced preference for the α-helical state at pathological Q-lengths. The Q-length-dependent structuring and rigidification could be mimicked in proteins with shorter Q-lengths by a decrease in temperature, indicating that lower temperatures similarly stabilize N17 and polyQ intramolecular contacts. The more rigid α-helical state of Httex1 with an expanded polyQ tract is expected to alter interactions with cellular proteins and modulate the toxic Httex1 misfolding process. We propose that the polyQ-dependent shift in the structural equilibrium may enable future therapeutic strategies that specifically target Httex1 with toxic Q-lengths.
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Affiliation(s)
- Jose M Bravo-Arredondo
- From the Departments of Physiology and Neuroscience and.,the Facultad de Ciencias Básicas, Ingeniería y Tecnología, Universidad Autónoma de Tlaxcala, Calzada Apizaquito S/N, 90300 Apizaco, Tlaxcala, Mexico
| | - Natalie C Kegulian
- Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033 and
| | - Thomas Schmidt
- Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033 and
| | | | - Alan J Situ
- From the Departments of Physiology and Neuroscience and
| | - Tobias S Ulmer
- From the Departments of Physiology and Neuroscience and.,Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033 and
| | - Ralf Langen
- From the Departments of Physiology and Neuroscience and .,Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033 and
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31
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Caulkins BG, Cervantes SA, Isas JM, Siemer AB. Dynamics of the Proline-Rich C-Terminus of Huntingtin Exon-1 Fibrils. J Phys Chem B 2018; 122:9507-9515. [PMID: 30252478 DOI: 10.1021/acs.jpcb.8b09213] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Intrinsically disordered protein domains not only are found in soluble proteins but also can be part of large protein complexes or protein aggregates. For example, several amyloid fibrils have intrinsically disordered domains framing a rigid β-sheet-rich core. These disordered domains can often be observed using solution NMR methods in combination with modest magic angle spinning and without perdeuteration. But how can these regions be detected using solution NMR methods when they are part of a fibril that is not tumbling isotropically in solution? Here we addressed this question by investigating the dynamic C-terminus of huntingtin exon-1 (HTTex1) fibrils that are important in Huntington's disease. We assigned the most dynamic regions of the C-terminus of three HTTex1 variants. On the basis of this assignment, we measured site-specific secondary chemical shifts, peak intensities, and R1, R'2, and R1ρ 15N relaxation rates. In addition, we determined the residual 1H-15N dipolar couplings of this region. Our results show that the dipolar couplings are averaged to a very high degree, resulting in an order parameter that is essentially zero. Together, our data show that the C-terminus of HTTex1 is intrinsically disordered and undergoes motions in the high picosecond to low nanosecond range.
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Affiliation(s)
- Bethany G Caulkins
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute , Keck School of Medicine of USC , 1501 San Pablo St. , Los Angeles , California 90033 , United States
| | - Silvia A Cervantes
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute , Keck School of Medicine of USC , 1501 San Pablo St. , Los Angeles , California 90033 , United States
| | - J Mario Isas
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute , Keck School of Medicine of USC , 1501 San Pablo St. , Los Angeles , California 90033 , United States
| | - Ansgar B Siemer
- Department of Physiology & Neuroscience, Zilkha Neurogenetic Institute , Keck School of Medicine of USC , 1501 San Pablo St. , Los Angeles , California 90033 , United States
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32
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Newcombe EA, Ruff KM, Sethi A, Ormsby AR, Ramdzan YM, Fox A, Purcell AW, Gooley PR, Pappu RV, Hatters DM. Tadpole-like Conformations of Huntingtin Exon 1 Are Characterized by Conformational Heterogeneity that Persists regardless of Polyglutamine Length. J Mol Biol 2018; 430:1442-1458. [PMID: 29627459 DOI: 10.1016/j.jmb.2018.03.031] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Revised: 03/21/2018] [Accepted: 03/25/2018] [Indexed: 11/30/2022]
Abstract
Soluble huntingtin exon 1 (Httex1) with expanded polyglutamine (polyQ) engenders neurotoxicity in Huntington's disease. To uncover the physical basis of this toxicity, we performed structural studies of soluble Httex1 for wild-type and mutant polyQ lengths. Nuclear magnetic resonance experiments show evidence for conformational rigidity across the polyQ region. In contrast, hydrogen-deuterium exchange shows absence of backbone amide protection, suggesting negligible persistence of hydrogen bonds. The seemingly conflicting results are explained by all-atom simulations, which show that Httex1 adopts tadpole-like structures with a globular head encompassing the N-terminal amphipathic and polyQ regions and the tail encompassing the C-terminal proline-rich region. The surface area of the globular domain increases monotonically with polyQ length. This stimulates sharp increases in gain-of-function interactions in cells for expanded polyQ, and one of these interactions is with the stress-granule protein Fus. Our results highlight plausible connections between Httex1 structure and routes to neurotoxicity.
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Affiliation(s)
- Estella A Newcombe
- Department of Biochemistry and Molecular Biology, and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC 3010, Australia
| | - Kiersten M Ruff
- Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in St. Louis, St Louis, MO 63130, USA
| | - Ashish Sethi
- Department of Biochemistry and Molecular Biology, and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC 3010, Australia
| | - Angelique R Ormsby
- Department of Biochemistry and Molecular Biology, and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC 3010, Australia
| | - Yasmin M Ramdzan
- Department of Biochemistry and Molecular Biology, and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC 3010, Australia
| | - Archa Fox
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, WA 6009, Australia
| | - Anthony W Purcell
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia
| | - Paul R Gooley
- Department of Biochemistry and Molecular Biology, and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC 3010, Australia
| | - Rohit V Pappu
- Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in St. Louis, St Louis, MO 63130, USA.
| | - Danny M Hatters
- Department of Biochemistry and Molecular Biology, and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, VIC 3010, Australia.
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33
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Posey AE, Ruff KM, Harmon TS, Crick SL, Li A, Diamond MI, Pappu RV. Profilin reduces aggregation and phase separation of huntingtin N-terminal fragments by preferentially binding to soluble monomers and oligomers. J Biol Chem 2018; 293:3734-3746. [PMID: 29358329 PMCID: PMC5846159 DOI: 10.1074/jbc.ra117.000357] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Revised: 01/16/2018] [Indexed: 11/06/2022] Open
Abstract
Huntingtin N-terminal fragments (Htt-NTFs) with expanded polyglutamine tracts form a range of neurotoxic aggregates that are associated with Huntington's disease. Here, we show that aggregation of Htt-NTFs, irrespective of polyglutamine length, yields at least three phases (designated M, S, and F) that are delineated by sharp concentration thresholds and distinct aggregate sizes and morphologies. We found that monomers and oligomers make up the soluble M phase, ∼25-nm spheres dominate in the soluble S phase, and long, linear fibrils make up the insoluble F phase. Previous studies showed that profilin, an abundant cellular protein, reduces Htt-NTF aggregation and toxicity in cells. We confirm that profilin achieves its cellular effects through direct binding to the C-terminal proline-rich region of Htt-NTFs. We show that profilin preferentially binds to Htt-NTF M-phase species and destabilizes aggregation and phase separation by shifting the concentration boundaries for phase separation to higher values through a process known as polyphasic linkage. Our experiments, aided by coarse-grained computer simulations and theoretical analysis, suggest that preferential binding of profilin to the M-phase species of Htt-NTFs is enhanced through a combination of specific interactions between profilin and polyproline segments and auxiliary interactions between profilin and polyglutamine tracts. Polyphasic linkage may be a general strategy that cells utilize to regulate phase behavior of aggregation-prone proteins. Accordingly, detailed knowledge of phase behavior and an understanding of how ligands modulate phase boundaries may pave the way for developing new therapeutics against a variety of aggregation-prone proteins.
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Affiliation(s)
- Ammon E Posey
- From the Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University, St. Louis, Missouri 63130
| | - Kiersten M Ruff
- From the Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University, St. Louis, Missouri 63130
| | - Tyler S Harmon
- From the Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University, St. Louis, Missouri 63130
| | - Scott L Crick
- From the Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University, St. Louis, Missouri 63130
| | - Aimin Li
- the Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63108
| | - Marc I Diamond
- the Center for Alzheimer's and Neurodegenerative Diseases, University of Texas Southwestern Medical Center, Dallas, Texas 75390, and
| | - Rohit V Pappu
- From the Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University, St. Louis, Missouri 63130,
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34
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Caterino M, Squillaro T, Montesarchio D, Giordano A, Giancola C, Melone MAB. Huntingtin protein: A new option for fixing the Huntington's disease countdown clock. Neuropharmacology 2018. [PMID: 29526547 DOI: 10.1016/j.neuropharm.2018.03.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Huntington's disease is a dreadful, incurable disorder. It springs from the autosomal dominant mutation in the first exon of the HTT gene, which encodes for the huntingtin protein (HTT) and results in progressive neurodegeneration. Thus far, all the attempted approaches to tackle the mutant HTT-induced toxicity causing this disease have failed. The mutant protein comes with the aberrantly expanded poly-glutamine tract. It is primarily to blame for the build-up of β-amyloid-like HTT aggregates, deleterious once broadened beyond the critical ∼35-37 repeats threshold. Recent experimental findings have provided valuable information on the molecular basis underlying this HTT-driven neurodegeneration. These findings indicate that the poly-glutamine siding regions and many post-translation modifications either abet or counter the poly-glutamine tract. This review provides an overall, up-to-date insight into HTT biophysics and structural biology, particularly discussing novel pharmacological options to specifically target the mutated protein and thus inhibit its functions and toxicity.
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Affiliation(s)
- Marco Caterino
- Department of Pharmacy, University of Napoli Federico II, Via D. Montesano 49, 80131, Napoli, Italy
| | - Tiziana Squillaro
- Department of Medical, Surgical, Neurological, Metabolic Sciences, and Aging, 2nd Division of Neurology, Center for Rare Diseases, University of Campania "Luigi Vanvitelli", Napoli, Italy; InterUniversity Center for Research in Neurosciences, University of Campania "Luigi Vanvitelli", Napoli, Italy
| | - Daniela Montesarchio
- InterUniversity Center for Research in Neurosciences, University of Campania "Luigi Vanvitelli", Napoli, Italy; Department of Chemical Sciences, University of Napoli Federico II, Via Cintia 21, 80126, Napoli, Italy
| | - Antonio Giordano
- Sbarro Institute for Cancer Research and Molecular Medicine, Department of Biology, Center for Biotechnology, College of Science and Technology, Temple University, Philadelphia, PA, USA; Department of Medicine, Surgery and Neuroscience University of Siena, Siena, Italy
| | - Concetta Giancola
- Department of Pharmacy, University of Napoli Federico II, Via D. Montesano 49, 80131, Napoli, Italy; InterUniversity Center for Research in Neurosciences, University of Campania "Luigi Vanvitelli", Napoli, Italy.
| | - Mariarosa A B Melone
- Department of Medical, Surgical, Neurological, Metabolic Sciences, and Aging, 2nd Division of Neurology, Center for Rare Diseases, University of Campania "Luigi Vanvitelli", Napoli, Italy; InterUniversity Center for Research in Neurosciences, University of Campania "Luigi Vanvitelli", Napoli, Italy; Sbarro Institute for Cancer Research and Molecular Medicine, Department of Biology, Center for Biotechnology, College of Science and Technology, Temple University, Philadelphia, PA, USA.
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35
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Pandey NK, Isas JM, Rawat A, Lee RV, Langen J, Pandey P, Langen R. The 17-residue-long N terminus in huntingtin controls stepwise aggregation in solution and on membranes via different mechanisms. J Biol Chem 2018; 293:2597-2605. [PMID: 29282287 PMCID: PMC5818184 DOI: 10.1074/jbc.m117.813667] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Revised: 12/19/2017] [Indexed: 01/05/2023] Open
Abstract
Aggregation of huntingtin protein arising from expanded polyglutamine (polyQ) sequences in the exon-1 region of mutant huntingtin plays a central role in the pathogenesis of Huntington's disease. The huntingtin aggregation pathways are of therapeutic and diagnostic interest, but obtaining critical information from the physiologically relevant htt exon-1 (Httex1) protein has been challenging. Using biophysical techniques and an expression and purification protocol that generates clean, monomeric Httex1, we identified and mapped three distinct aggregation pathways: 1) unseeded in solution; 2) seeded in solution; and 3) membrane-mediated. In solution, aggregation proceeded in a highly stepwise manner, in which the individual domains (N terminus containing 17 amino acids (N17), polyQ, and proline-rich domain (PRD)) become ordered at very different rates. The aggregation was initiated by an early oligomer requiring a pathogenic, expanded Gln length and N17 α-helix formation. In the second phase, β-sheet forms in the polyQ. The slowest step is the final structural maturation of the PRD. This stepwise mechanism could be bypassed by seeding, which potently accelerated aggregation and was a prerequisite for prion-like spreading in vivo Remarkably, membranes could catalyze aggregation even more potently than seeds, in a process that caused significant membrane damage. The N17 governed membrane-mediated aggregation by anchoring Httex1 to the membrane, enhancing local concentration and promoting collision via two-dimensional diffusion. Considering its central roles in solution and in membrane-mediated aggregation, the N17 represents an attractive target for inhibiting multiple pathways. Our approach should help evaluate such inhibitors and identify diagnostic markers for the misfolded forms identified here.
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Affiliation(s)
- Nitin K Pandey
- From the Departments of Physiology and Neuroscience and of Biochemistry and Molecular Medicine. Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - J Mario Isas
- From the Departments of Physiology and Neuroscience and of Biochemistry and Molecular Medicine. Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Anoop Rawat
- From the Departments of Physiology and Neuroscience and of Biochemistry and Molecular Medicine. Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Rachel V Lee
- From the Departments of Physiology and Neuroscience and of Biochemistry and Molecular Medicine. Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Jennifer Langen
- From the Departments of Physiology and Neuroscience and of Biochemistry and Molecular Medicine. Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Priyatama Pandey
- From the Departments of Physiology and Neuroscience and of Biochemistry and Molecular Medicine. Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Ralf Langen
- From the Departments of Physiology and Neuroscience and of Biochemistry and Molecular Medicine. Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
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36
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Phosphorylation of huntingtin at residue T3 is decreased in Huntington's disease and modulates mutant huntingtin protein conformation. Proc Natl Acad Sci U S A 2017; 114:E10809-E10818. [PMID: 29162692 PMCID: PMC5740681 DOI: 10.1073/pnas.1705372114] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Posttranslational modifications can have profound effects on the biological and biophysical properties of proteins associated with misfolding and aggregation. However, their detection and quantification in clinical samples and an understanding of the mechanisms underlying the pathological properties of misfolding- and aggregation-prone proteins remain a challenge for diagnostics and therapeutics development. We have applied an ultrasensitive immunoassay platform to develop and validate a quantitative assay for detecting a posttranslational modification (phosphorylation at residue T3) of a protein associated with polyglutamine repeat expansion, namely Huntingtin, and characterized its presence in a variety of preclinical and clinical samples. We find that T3 phosphorylation is greatly reduced in samples from Huntington's disease models and in Huntington's disease patients, and we provide evidence that bona-fide T3 phosphorylation alters Huntingtin exon 1 protein conformation and aggregation properties. These findings have significant implications for both mechanisms of disease pathogenesis and the development of therapeutics and diagnostics for Huntington's disease.
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37
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Warner JB, Ruff KM, Tan PS, Lemke EA, Pappu RV, Lashuel HA. Monomeric Huntingtin Exon 1 Has Similar Overall Structural Features for Wild-Type and Pathological Polyglutamine Lengths. J Am Chem Soc 2017; 139:14456-14469. [PMID: 28937758 PMCID: PMC5677759 DOI: 10.1021/jacs.7b06659] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Indexed: 12/22/2022]
Abstract
Huntington's disease is caused by expansion of a polyglutamine (polyQ) domain within exon 1 of the huntingtin gene (Httex1). The prevailing hypothesis is that the monomeric Httex1 protein undergoes sharp conformational changes as the polyQ length exceeds a threshold of 36-37 residues. Here, we test this hypothesis by combining novel semi-synthesis strategies with state-of-the-art single-molecule Förster resonance energy transfer measurements on biologically relevant, monomeric Httex1 proteins of five different polyQ lengths. Our results, integrated with atomistic simulations, negate the hypothesis of a sharp, polyQ length-dependent change in the structure of monomeric Httex1. Instead, they support a continuous global compaction with increasing polyQ length that derives from increased prominence of the globular polyQ domain. Importantly, we show that monomeric Httex1 adopts tadpole-like architectures for polyQ lengths below and above the pathological threshold. Our results suggest that higher order homotypic and/or heterotypic interactions within distinct sub-populations of neurons, which are inevitable at finite cellular concentrations, are likely to be the main source of sharp polyQ length dependencies of HD.
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Affiliation(s)
- John B. Warner
- Laboratory
of Molecular and Chemical Biology of Neurodegeneration, Brain Mind
Institute, Station 19, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Kiersten M. Ruff
- Department
of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Piau Siong Tan
- Structural
and Computational Biology Unit, Cell Biology and Biophysics Unit, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Edward A. Lemke
- Structural
and Computational Biology Unit, Cell Biology and Biophysics Unit, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Rohit V. Pappu
- Department
of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Hilal A. Lashuel
- Laboratory
of Molecular and Chemical Biology of Neurodegeneration, Brain Mind
Institute, Station 19, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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38
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Bäuerlein FJB, Saha I, Mishra A, Kalemanov M, Martínez-Sánchez A, Klein R, Dudanova I, Hipp MS, Hartl FU, Baumeister W, Fernández-Busnadiego R. In Situ Architecture and Cellular Interactions of PolyQ Inclusions. Cell 2017; 171:179-187.e10. [PMID: 28890085 DOI: 10.1016/j.cell.2017.08.009] [Citation(s) in RCA: 196] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Revised: 06/30/2017] [Accepted: 08/07/2017] [Indexed: 02/06/2023]
Abstract
Expression of many disease-related aggregation-prone proteins results in cytotoxicity and the formation of large intracellular inclusion bodies. To gain insight into the role of inclusions in pathology and the in situ structure of protein aggregates inside cells, we employ advanced cryo-electron tomography methods to analyze the structure of inclusions formed by polyglutamine (polyQ)-expanded huntingtin exon 1 within their intact cellular context. In primary mouse neurons and immortalized human cells, polyQ inclusions consist of amyloid-like fibrils that interact with cellular endomembranes, particularly of the endoplasmic reticulum (ER). Interactions with these fibrils lead to membrane deformation, the local impairment of ER organization, and profound alterations in ER membrane dynamics at the inclusion periphery. These results suggest that aberrant interactions between fibrils and endomembranes contribute to the deleterious cellular effects of protein aggregation. VIDEO ABSTRACT.
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Affiliation(s)
- Felix J B Bäuerlein
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Itika Saha
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Archana Mishra
- Department of Molecules, Signaling, and Development, Max Planck Institute of Neurobiology, 82152 Martinsried, Germany
| | - Maria Kalemanov
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany; Graduate School of Quantitative Biosciences Munich, 81337 Munich, Germany
| | - Antonio Martínez-Sánchez
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Rüdiger Klein
- Department of Molecules, Signaling, and Development, Max Planck Institute of Neurobiology, 82152 Martinsried, Germany; Munich Cluster for Systems Neurology (SyNergy), 80336 Munich, Germany
| | - Irina Dudanova
- Department of Molecules, Signaling, and Development, Max Planck Institute of Neurobiology, 82152 Martinsried, Germany
| | - Mark S Hipp
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany; Munich Cluster for Systems Neurology (SyNergy), 80336 Munich, Germany
| | - F Ulrich Hartl
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany; Munich Cluster for Systems Neurology (SyNergy), 80336 Munich, Germany.
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
| | - Rubén Fernández-Busnadiego
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
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39
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Daldin M, Fodale V, Cariulo C, Azzollini L, Verani M, Martufi P, Spiezia MC, Deguire SM, Cherubini M, Macdonald D, Weiss A, Bresciani A, Vonsattel JPG, Petricca L, Marsh JL, Gines S, Santimone I, Marano M, Lashuel HA, Squitieri F, Caricasole A. Polyglutamine expansion affects huntingtin conformation in multiple Huntington's disease models. Sci Rep 2017; 7:5070. [PMID: 28698602 PMCID: PMC5505970 DOI: 10.1038/s41598-017-05336-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Accepted: 06/14/2017] [Indexed: 12/29/2022] Open
Abstract
Conformational changes in disease-associated or mutant proteins represent a key pathological aspect of Huntington’s disease (HD) and other protein misfolding diseases. Using immunoassays and biophysical approaches, we and others have recently reported that polyglutamine expansion in purified or recombinantly expressed huntingtin (HTT) proteins affects their conformational properties in a manner dependent on both polyglutamine repeat length and temperature but independent of HTT protein fragment length. These findings are consistent with the HD mutation affecting structural aspects of the amino-terminal region of the protein, and support the concept that modulating mutant HTT conformation might provide novel therapeutic and diagnostic opportunities. We now report that the same conformational TR-FRET based immunoassay detects polyglutamine- and temperature-dependent changes on the endogenously expressed HTT protein in peripheral tissues and post-mortem HD brain tissue, as well as in tissues from HD animal models. We also find that these temperature- and polyglutamine-dependent conformational changes are sensitive to bona-fide phosphorylation on S13 and S16 within the N17 domain of HTT. These findings provide key clinical and preclinical relevance to the conformational immunoassay, and provide supportive evidence for its application in the development of therapeutics aimed at correcting the conformation of polyglutamine-expanded proteins as well as the pharmacodynamics readouts to monitor their efficacy in preclinical models and in HD patients.
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Affiliation(s)
- Manuel Daldin
- IRBM Science Park, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy
| | - Valentina Fodale
- IRBM Science Park, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy.,IRBM Promidis, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy
| | - Cristina Cariulo
- IRBM Science Park, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy
| | - Lucia Azzollini
- IRBM Science Park, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy.,IRBM Promidis, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy
| | - Margherita Verani
- IRBM Science Park, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy.,IRBM Promidis, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy
| | - Paola Martufi
- IRBM Science Park, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy
| | | | - Sean M Deguire
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Station 19, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
| | - Marta Cherubini
- Departamento de Ciencias Biomedicas, Facultat de Medicina, Instituto de Neurociencias, Universitat de Barcelona, Barcelona, Spain
| | | | - Andreas Weiss
- IRBM Promidis, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy.,Evotec AG, Manfred Eigen Campus, Hamburg, Germany
| | - Alberto Bresciani
- IRBM Science Park, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy
| | - Jean-Paul Gerard Vonsattel
- Taub Institute for Research on Alzheimer's disease and the Aging Brain, Columbia University Medical Center, 710 West 168th Street, New York, NY, 10032, USA
| | - Lara Petricca
- IRBM Science Park, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy.,IRBM Promidis, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy
| | - J Lawrence Marsh
- Department of Developmental and Cell Biology, University of California, Irvine, 92697, USA
| | - Silvia Gines
- Departamento de Ciencias Biomedicas, Facultat de Medicina, Instituto de Neurociencias, Universitat de Barcelona, Barcelona, Spain
| | - Iolanda Santimone
- Huntington and Rare Diseases Unit, IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Massimo Marano
- Huntington and Rare Diseases Unit, IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Hilal A Lashuel
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Station 19, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
| | - Ferdinando Squitieri
- Huntington and Rare Diseases Unit, IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Andrea Caricasole
- IRBM Science Park, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy. .,IRBM Promidis, Via Pontina km 30.600, 00071, Pomezia, Rome, Italy.
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40
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Isas JM, Langen A, Isas MC, Pandey NK, Siemer AB. Formation and Structure of Wild Type Huntingtin Exon-1 Fibrils. Biochemistry 2017. [PMID: 28621522 DOI: 10.1021/acs.biochem.7b00138] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The fact that the heritable neurodegenerative disorder Huntington's disease (HD) is autosomal dominant means that there is one wild type and one mutant allele in most HD patients. The CAG repeat expansion in the exon 1 of the protein huntingtin (HTTex1) that causes the disease leads to the formation of HTT fibrils in vitro and vivo. An important question for understanding the molecular mechanism of HD is which role wild type HTT plays for the formation, propagation, and structure of these HTT fibrils. Here we report that fibrils of mutant HTTex1 are able to seed the aggregation of wild type HTTex1 into amyloid fibrils, which in turn can seed the fibril formation of mutant HTTex1. Solid-state NMR and electron paramagnetic resonance data showed that wild type HTTex1 fibrils closely resemble the structure of mutant fibrils, with small differences indicating a less extended fibril core. These data suggest that wild type fibrils can faithfully perpetuate the structure of mutant fibrils in HD. However, wild type HTTex1 monomers have a much higher equilibrium solubility compared to mutant HTTex1, and only a small fraction incorporates into fibrils.
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Affiliation(s)
- J Mario Isas
- Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , Los Angeles, California, United States
| | - Andreas Langen
- Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , Los Angeles, California, United States
| | - Myles C Isas
- Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , Los Angeles, California, United States
| | - Nitin K Pandey
- Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , Los Angeles, California, United States
| | - Ansgar B Siemer
- Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , Los Angeles, California, United States
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Chaibva M, Jawahery S, Pilkington AW, Arndt JR, Sarver O, Valentine S, Matysiak S, Legleiter J. Acetylation within the First 17 Residues of Huntingtin Exon 1 Alters Aggregation and Lipid Binding. Biophys J 2017; 111:349-362. [PMID: 27463137 DOI: 10.1016/j.bpj.2016.06.018] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Revised: 06/06/2016] [Accepted: 06/15/2016] [Indexed: 02/06/2023] Open
Abstract
Huntington's disease (HD) is a genetic neurodegenerative disorder caused by an expanded polyglutamine (polyQ) domain near the N-terminus of the huntingtin (htt) protein. Expanded polyQ leads to htt aggregation. The first 17 amino acids (Nt(17)) in htt comprise a lipid-binding domain that undergoes a number of posttranslational modifications that can modulate htt toxicity and subcellular localization. As there are three lysines within Nt(17), we evaluated the impact of lysine acetylation on htt aggregation in solution and on model lipid bilayers. Acetylation of htt-exon1(51Q) and synthetic truncated htt-exon 1 mimicking peptides (Nt(17)-Q35-P10-KK) was achieved using a selective covalent label, sulfo-N-hydroxysuccinimide (NHSA). With this treatment, all three lysine residues (K6, K9, and K15) in Nt(17) were significantly acetylated. N-terminal htt acetylation retarded fibril formation in solution and promoted the formation of larger globular aggregates. Acetylated htt also bound lipid membranes and disrupted the lipid bilayer morphology less aggressively compared with the wild-type. Computational studies provided mechanistic insights into how acetylation alters the interaction of Nt(17) with lipid membranes. Our results highlight that N-terminal acetylation influences the aggregation of htt and its interaction with lipid bilayers.
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Affiliation(s)
- Maxmore Chaibva
- The C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia
| | - Sudi Jawahery
- Fischell Department of Bioengineering, University of Maryland, College Park, Maryland
| | - Albert W Pilkington
- The C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia
| | - James R Arndt
- The C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia
| | - Olivia Sarver
- The C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia
| | - Stephen Valentine
- The C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia
| | - Silvina Matysiak
- Fischell Department of Bioengineering, University of Maryland, College Park, Maryland; Biophysics Program, Institute for Physical Chemistry and Technology, University of Maryland, College Park, Maryland.
| | - Justin Legleiter
- The C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia; NanoSAFE, West Virginia University, Morgantown, West Virginia; Center for Neurosciences, West Virginia University, Morgantown, West Virginia.
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42
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Fibril polymorphism affects immobilized non-amyloid flanking domains of huntingtin exon1 rather than its polyglutamine core. Nat Commun 2017; 8:15462. [PMID: 28537272 PMCID: PMC5458082 DOI: 10.1038/ncomms15462] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Accepted: 03/31/2017] [Indexed: 02/07/2023] Open
Abstract
Polyglutamine expansion in the huntingtin protein is the primary genetic cause of Huntington's disease (HD). Fragments coinciding with mutant huntingtin exon1 aggregate in vivo and induce HD-like pathology in mouse models. The resulting aggregates can have different structures that affect their biochemical behaviour and cytotoxic activity. Here we report our studies of the structure and functional characteristics of multiple mutant htt exon1 fibrils by complementary techniques, including infrared and solid-state NMR spectroscopies. Magic-angle-spinning NMR reveals that fibrillar exon1 has a partly mobile α-helix in its aggregation-accelerating N terminus, and semi-rigid polyproline II helices in the proline-rich flanking domain (PRD). The polyglutamine-proximal portions of these domains are immobilized and clustered, limiting access to aggregation-modulating antibodies. The polymorphic fibrils differ in their flanking domains rather than the polyglutamine amyloid structure. They are effective at seeding polyglutamine aggregation and exhibit cytotoxic effects when applied to neuronal cells. Huntington's disease is caused by a polyglutamine stretch expansion in the first exon of huntingtin. Here, the authors use infrared spectroscopy and solid-state NMR and show that polymorphic huntingtin exon1 fibres differ in their flanking regions but not their core polyglutamine amyloid structures.
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43
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Lucato CM, Lupton CJ, Halls ML, Ellisdon AM. Amyloidogenicity at a Distance: How Distal Protein Regions Modulate Aggregation in Disease. J Mol Biol 2017; 429:1289-1304. [PMID: 28342736 DOI: 10.1016/j.jmb.2017.03.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Revised: 03/12/2017] [Accepted: 03/14/2017] [Indexed: 12/14/2022]
Abstract
The misfolding of proteins to form amyloid is a key pathological feature of several progressive, and currently incurable, diseases. A mechanistic understanding of the pathway from soluble, native protein to insoluble amyloid is crucial for therapeutic design, and recent efforts have helped to elucidate the key molecular events that trigger protein misfolding. Generally, either global or local structural perturbations occur early in amyloidogenesis to expose aggregation-prone regions of the protein that can then self-associate to form toxic oligomers. Surprisingly, these initiating structural changes are often caused or influenced by protein regions distal to the classically amyloidogenic sequences. Understanding the importance of these distal regions in the pathogenic process has highlighted many remaining knowledge gaps regarding the precise molecular events that occur in classic aggregation pathways. In this review, we discuss how these distal regions can influence aggregation in disease and the recent technical and conceptual advances that have allowed this insight.
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Affiliation(s)
- Christina M Lucato
- Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia; Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, Victoria 3800, Australia
| | - Christopher J Lupton
- Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia; Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, Victoria 3800, Australia
| | - Michelle L Halls
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| | - Andrew M Ellisdon
- Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia; Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, Victoria 3800, Australia.
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44
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Adegbuyiro A, Sedighi F, Pilkington AW, Groover S, Legleiter J. Proteins Containing Expanded Polyglutamine Tracts and Neurodegenerative Disease. Biochemistry 2017; 56:1199-1217. [PMID: 28170216 DOI: 10.1021/acs.biochem.6b00936] [Citation(s) in RCA: 90] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Several hereditary neurological and neuromuscular diseases are caused by an abnormal expansion of trinucleotide repeats. To date, there have been 10 of these trinucleotide repeat disorders associated with an expansion of the codon CAG encoding glutamine (Q). For these polyglutamine (polyQ) diseases, there is a critical threshold length of the CAG repeat required for disease, and further expansion beyond this threshold is correlated with age of onset and symptom severity. PolyQ expansion in the translated proteins promotes their self-assembly into a variety of oligomeric and fibrillar aggregate species that accumulate into the hallmark proteinaceous inclusion bodies associated with each disease. Here, we review aggregation mechanisms of proteins with expanded polyQ-tracts, structural consequences of expanded polyQ ranging from monomers to fibrillar aggregates, the impact of protein context and post-translational modifications on aggregation, and a potential role for lipid membranes in aggregation. As the pathogenic mechanisms that underlie these disorders are often classified as either a gain of toxic function or loss of normal protein function, some toxic mechanisms associated with mutant polyQ tracts will also be discussed.
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Affiliation(s)
- Adewale Adegbuyiro
- The C. Eugene Bennett Department of Chemistry, 217 Clark Hall, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Faezeh Sedighi
- The C. Eugene Bennett Department of Chemistry, 217 Clark Hall, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Albert W Pilkington
- The C. Eugene Bennett Department of Chemistry, 217 Clark Hall, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Sharon Groover
- The C. Eugene Bennett Department of Chemistry, 217 Clark Hall, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Justin Legleiter
- The C. Eugene Bennett Department of Chemistry, 217 Clark Hall, West Virginia University , Morgantown, West Virginia 26506, United States.,Blanchette Rockefeller Neurosciences Institute, Robert C. Byrd Health Sciences Center, P.O. Box 9304, West Virginia University , Morgantown, West Virginia 26506, United States.,NanoSAFE, P.O. Box 6223, West Virginia University , Morgantown, West Virginia 26506, United States
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45
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Figueira I, Menezes R, Macedo D, Costa I, Nunes dos Santos C. Polyphenols Beyond Barriers: A Glimpse into the Brain. Curr Neuropharmacol 2017; 15:562-594. [PMID: 27784225 PMCID: PMC5543676 DOI: 10.2174/1570159x14666161026151545] [Citation(s) in RCA: 74] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2015] [Revised: 08/02/2016] [Accepted: 09/28/2016] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Ageing can be simply defined as the process of becoming older, which is genetically determined but also environmentally modulated. With the continuous increase of life expectancy, quality of life during ageing has become one of the biggest challenges of developed countries. The quest for a healthy ageing has led to the extensive study of plant polyphenols with the aim to prevent age-associated deterioration and diseases, including neurodegenerative diseases. The world of polyphenols has fascinated researchers over the past decades, and in vitro, cell-based, animal and human studies have attempted to unravel the mechanisms behind dietary polyphenols neuroprotection. METHODS In this review, we compiled some of the extensive and ever-growing research in the field, highlighting some of the most recent trends in the area. RESULTS The main findings regarding polypolyphenols neuroprotective potential performed using in vitro, cellular and animal studies, as well as human trials are covered in this review. Concepts like bioavailability, polyphenols biotransformation, transport of dietary polyphenols across barriers, including the blood-brain barrier, are here explored. CONCLUSION The diversity and holistic properties of polypolyphenol present them as an attractive alternative for the treatment of multifactorial diseases, where a multitude of cellular pathways are disrupted. The underlying mechanisms of polypolyphenols for nutrition or therapeutic applications must be further consolidated, however there is strong evidence of their beneficial impact on brain function during ageing. Nevertheless, only the tip of the iceberg of nutritional and pharmacological potential of dietary polyphenols is hitherto understood and further research needs to be done to fill the gaps in pursuing a healthy ageing.
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Affiliation(s)
- Inês Figueira
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras
| | - Regina Menezes
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras
- iBET, Instituto de Biologia Experimental e Tecnológica, Apartado 12, 2781-901 Oeiras
| | - Diana Macedo
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras
- iBET, Instituto de Biologia Experimental e Tecnológica, Apartado 12, 2781-901 Oeiras
| | - Inês Costa
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras
- iBET, Instituto de Biologia Experimental e Tecnológica, Apartado 12, 2781-901 Oeiras
| | - Cláudia Nunes dos Santos
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras
- iBET, Instituto de Biologia Experimental e Tecnológica, Apartado 12, 2781-901 Oeiras
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46
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Identification and Structural Characterization of the N-terminal Amyloid Core of Orb2 isoform A. Sci Rep 2016; 6:38265. [PMID: 27922050 PMCID: PMC5138630 DOI: 10.1038/srep38265] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Accepted: 11/07/2016] [Indexed: 12/12/2022] Open
Abstract
Orb2 is a functional amyloid that plays a key role in Drosophila long-term memory formation. Orb2 has two isoforms that differ in their N-termini. The N-terminus of the A isoform (Orb2A) that precedes its Q-rich prion-like domain has been shown to be important for Orb2 aggregation and long-term memory. However, besides the fact that it forms fibrillar aggregates, structural information of Orb2 is largely absent. To understand the importance of the N-terminus of Orb2A and its relation to the fibril core, we recorded solid-state NMR and EPR data on fibrils formed by the first 88 residues of Orb2A (Orb2A88). These data show that the N-terminus of Orb2A not only promotes the formation of fibrils, but also forms the fibril core of Orb2A88. This fibril core has an in-register parallel β-sheet structure and does not include the Q-rich, prion-like domain of Orb2. The Q-rich domain is part of the unstructured region, which becomes increasingly dynamic towards the C-terminus.
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47
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Shen K, Calamini B, Fauerbach JA, Ma B, Shahmoradian SH, Serrano Lachapel IL, Chiu W, Lo DC, Frydman J. Control of the structural landscape and neuronal proteotoxicity of mutant Huntingtin by domains flanking the polyQ tract. eLife 2016; 5. [PMID: 27751235 PMCID: PMC5135392 DOI: 10.7554/elife.18065] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2016] [Accepted: 10/17/2016] [Indexed: 12/29/2022] Open
Abstract
Many neurodegenerative diseases are linked to amyloid aggregation. In Huntington’s disease (HD), neurotoxicity correlates with an increased aggregation propensity of a polyglutamine (polyQ) expansion in exon 1 of mutant huntingtin protein (mHtt). Here we establish how the domains flanking the polyQ tract shape the mHtt conformational landscape in vitro and in neurons. In vitro, the flanking domains have opposing effects on the conformation and stabilities of oligomers and amyloid fibrils. The N-terminal N17 promotes amyloid fibril formation, while the C-terminal Proline Rich Domain destabilizes fibrils and enhances oligomer formation. However, in neurons both domains act synergistically to engage protective chaperone and degradation pathways promoting mHtt proteostasis. Surprisingly, when proteotoxicity was assessed in rat corticostriatal brain slices, either flanking region alone sufficed to generate a neurotoxic conformation, while the polyQ tract alone exhibited minimal toxicity. Linking mHtt structural properties to its neuronal proteostasis should inform new strategies for neuroprotection in polyQ-expansion diseases. DOI:http://dx.doi.org/10.7554/eLife.18065.001 Huntington’s disease is a neurodegenerative disorder in which misshapen proteins accumulate in the brain and kill neurons. The misshapen proteins form as a result of specific mutations in the gene that encodes a protein called huntingtin. These mutations result in a region of the protein called the polyQ tract being longer than normal. Other regions of huntingtin that are near to the polyQ tract can dramatically change the behavior of the mutant protein. Shen et al. investigated how these regions control the shape of mutant huntingtin and how this affects the toxicity of the mutant protein in neurons. The experiments found that the two regions on either side of the polyQ tract dramatically change the shape of mutant huntingtin proteins. In the absence of these flanking regions, the extended polyQ region is not very toxic, demonstrating that the flanking sequences play important roles in generating the toxic protein shapes. These flanking regions help mutant huntingtin to form a particular shape that was strongly linked with the death of neurons in rat brain slices. The flanking regions also change the way that the cellular machinery in neurons recognizes mutated huntingtin proteins and acts to prevent them from causing harm. Misshapen forms of other proteins are responsible for causing other neurodegenerative diseases, including Alzheimer’s and Parkinson’s diseases. Therefore, the findings of Shen et al. may help researchers to develop new drugs for these conditions, as well as for Huntingdon’s disease. DOI:http://dx.doi.org/10.7554/eLife.18065.002
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Affiliation(s)
- Koning Shen
- Department of Biology, Stanford University, Stanford, United States.,Department of Genetics, Stanford University, Stanford, United States
| | - Barbara Calamini
- Center for Drug Discovery, Department of Neurobiology, Duke University Medical Center, Durham, United States
| | - Jonathan A Fauerbach
- Department of Biology, Stanford University, Stanford, United States.,Department of Genetics, Stanford University, Stanford, United States
| | - Boxue Ma
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, United States
| | - Sarah H Shahmoradian
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, United States
| | - Ivana L Serrano Lachapel
- Department of Biology, Stanford University, Stanford, United States.,Department of Genetics, Stanford University, Stanford, United States
| | - Wah Chiu
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, United States
| | - Donald C Lo
- Center for Drug Discovery, Department of Neurobiology, Duke University Medical Center, Durham, United States
| | - Judith Frydman
- Department of Biology, Stanford University, Stanford, United States.,Department of Genetics, Stanford University, Stanford, United States
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48
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Nanoscale studies link amyloid maturity with polyglutamine diseases onset. Sci Rep 2016; 6:31155. [PMID: 27499269 PMCID: PMC4976327 DOI: 10.1038/srep31155] [Citation(s) in RCA: 101] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 07/01/2016] [Indexed: 02/06/2023] Open
Abstract
The presence of expanded poly-glutamine (polyQ) repeats in proteins is directly linked to the pathogenesis of several neurodegenerative diseases, including Huntington’s disease. However, the molecular and structural basis underlying the increased toxicity of aggregates formed by proteins containing expanded polyQ repeats remain poorly understood, in part due to the size and morphological heterogeneity of the aggregates they form in vitro. To address this knowledge gap and technical limitations, we investigated the structural, mechanical and morphological properties of fibrillar aggregates at the single molecule and nanometer scale using the first exon of the Huntingtin protein as a model system (Exon1). Our findings demonstrate a direct correlation of the morphological and mechanical properties of Exon1 aggregates with their structural organization at the single aggregate and nanometric scale and provide novel insights into the molecular and structural basis of Huntingtin Exon1 aggregation and toxicity.
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49
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Vieweg S, Ansaloni A, Wang ZM, Warner JB, Lashuel HA. An Intein-based Strategy for the Production of Tag-free Huntingtin Exon 1 Proteins Enables New Insights into the Polyglutamine Dependence of Httex1 Aggregation and Fibril Formation. J Biol Chem 2016; 291:12074-86. [PMID: 27002149 PMCID: PMC4933259 DOI: 10.1074/jbc.m116.713982] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Revised: 03/18/2016] [Indexed: 12/25/2022] Open
Abstract
The first exon of the Huntingtin protein (Httex1) is one of the most actively studied Htt fragments because its overexpression in R6/2 transgenic mice has been shown to recapitulate several key features of Huntington disease. However, the majority of biophysical studies of Httex1 are based on assessing the structure and aggregation of fusion constructs where Httex1 is fused to large proteins, such as glutathione S-transferase, maltose-binding protein, or thioredoxin, or released in solution upon in situ cleavage of these proteins. Herein, we report an intein-based strategy that allows, for the first time, the rapid and efficient production of native tag-free Httex1 with polyQ repeats ranging from 7Q to 49Q. Aggregation studies on these proteins enabled us to identify interesting polyQ-length-dependent effects on Httex1 oligomer and fibril formation that were previously not observed using Httex1 fusion proteins or Httex1 proteins produced by in situ cleavage of fusion proteins. Our studies revealed the inability of Httex1-7Q/15Q to undergo amyloid fibril formation and an inverse correlation between fibril length and polyQ repeat length, suggesting possible polyQ length-dependent differences in the structural properties of the Httex1 aggregates. Altogether, our findings underscore the importance of working with tag-free Httex1 proteins and indicate that model systems based on non-native Httex1 sequences may not accurately reproduce the effect of polyQ repeat length and solution conditions on Httex1 aggregation kinetics and structural properties.
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Affiliation(s)
- Sophie Vieweg
- From the Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland and
| | - Annalisa Ansaloni
- From the Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland and
| | - Zhe-Ming Wang
- From the Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland and
| | - John B Warner
- From the Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland and
| | - Hilal A Lashuel
- From the Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland and Qatar Biomedical Research Institute (QBRI), Hamad bin Khalifa University (HBKU), 5825 Doha, Qatar
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50
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Arndt JR, Chaibva M, Legleiter J. The emerging role of the first 17 amino acids of huntingtin in Huntington's disease. Biomol Concepts 2016; 6:33-46. [PMID: 25741791 DOI: 10.1515/bmc-2015-0001] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2015] [Accepted: 02/09/2015] [Indexed: 01/01/2023] Open
Abstract
Huntington's disease (HD) is caused by a polyglutamine (polyQ) domain that is expanded beyond a critical threshold near the N-terminus of the huntingtin (htt) protein, directly leading to htt aggregation. While full-length htt is a large (on the order of ∼350 kDa) protein, it is proteolyzed into a variety of N-terminal fragments that accumulate in oligomers, fibrils, and larger aggregates. It is clear that polyQ length is a key determinant of htt aggregation and toxicity. However, the flanking sequences around the polyQ domain, such as the first 17 amino acids on the N terminus (Nt17), influence aggregation, aggregate stability, influence other important biochemical properties of the protein and ultimately its role in pathogenesis. Here, we review the impact of Nt17 on htt aggregation mechanisms and kinetics, structural properties of Nt17 in both monomeric and aggregate forms, the potential role of posttranslational modifications (PTMs) that occur in Nt17 in HD, and the function of Nt17 as a membrane targeting domain.
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