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Kegulian NC, Isas MJ, Chung SS, Pandey NK, Bravo JM, Langen R. Conformational Shifts in Huntingtin Exon 1 Monomer are Dependent on Temperature and Polyglutamine Length. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.2859] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Pandey NK, Mario Isas J, Langen R. Studies on Domain Specific Aggregation Behavior of Huntingtin Exon1. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.1190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Levine ZA, Okada A, Teranishi K, Langen R, Shea JE. Reducing IAPP Aggregation with Mitochondrial Humanin Peptides; Results from Simulations and Experiments. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Dearborn AD, Wall JS, Cheng N, Heymann JB, Kajava AV, Varkey J, Langen R, Steven AC. α-Synuclein Amyloid Fibrils with Two Entwined, Asymmetrically Associated Protofibrils. J Biol Chem 2015; 291:2310-8. [PMID: 26644467 DOI: 10.1074/jbc.m115.698787] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Indexed: 11/06/2022] Open
Abstract
Parkinson disease and other progressive neurodegenerative conditions are characterized by the intracerebral presence of Lewy bodies, containing amyloid fibrils of α-synuclein. We used cryo-electron microscopy and scanning transmission electron microscopy (STEM) to study in vitro-assembled fibrils. These fibrils are highly polymorphic. Focusing on twisting fibrils with an inter-crossover spacing of 77 nm, our reconstructions showed them to consist of paired protofibrils. STEM mass per length data gave one subunit per 0.47 nm axial rise per protofibril, consistent with a superpleated β-structure. The STEM images show two thread-like densities running along each of these fibrils, which we interpret as ladders of metal ions. These threads confirmed the two-protofibril architecture of the 77-nm twisting fibrils and allowed us to identify this morphotype in STEM micrographs. Some other, but not all, fibril morphotypes also exhibit dense threads, implying that they also present a putative metal binding site. We propose a molecular model for the protofibril and suggest that polymorphic variant fibrils have different numbers of protofibrils that are associated differently.
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Ambroso MR, Haworth IS, Langen R. Structural Characterization of Membrane-Curving Proteins: Site-Directed Spin Labeling, EPR, and Computational Refinement. Methods Enzymol 2015; 564:259-88. [PMID: 26477254 DOI: 10.1016/bs.mie.2015.07.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/08/2022]
Abstract
Endocytosis and other membrane remodeling processes require the coordinated generation of different membrane shapes. Proteins capable of manipulating lipid bilayers mediate these events using mechanisms that are not fully understood. Progress is limited by the small number of structures solved for proteins bound to different membrane shapes and tools capable of resolving such information. However, recent studies have shown site-directed spin labeling (SDSL) in combination with electron paramagnetic resonance (EPR) to be capable of obtaining high-resolution structural information for proteins bound to different membrane shapes. This technique can be applied to proteins with no known structure or proteins with structures known in solution. By refining the data obtained by EPR with computational modeling, 3D structures or structural models of membrane-bound proteins can be generated. In this chapter, we highlight the basic considerations and steps required to investigate the structures of membrane-bound proteins using SDSL, EPR, and computational refinement.
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Beasley KN, Sutch BT, Hatmal MM, Langen R, Qin PZ, Haworth IS. Computer Modeling of Spin Labels: NASNOX, PRONOX, and ALLNOX. Methods Enzymol 2015; 563:569-93. [PMID: 26478499 DOI: 10.1016/bs.mie.2015.07.021] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Measurement of distances between spin labels using electron paramagnetic resonance with the double electron-electron resonance (DEER) technique is an important method for evaluation of biomolecular structures. Computation of interlabel distances is of value for experimental planning, validation of known structures using DEER-measured distances, and determination of theoretical data for comparison with experiment. This requires steps of building labels at two defined sites on proteins, DNA or RNA; calculation of allowable label conformers based on rotation around torsional angles; computation of pairwise interlabel distances on a per conformer basis; and calculation of an average distance between the two label ensembles. We have described and validated two programs for this purpose: NASNOX, which permits computation of distances between R5 labels on DNA or RNA; and PRONOX, which similarly computes distances between R1 labels on proteins. However, these programs are limited to a specific single label and single target types. Therefore, we have developed a program, which we refer to as ALLNOX (Addition of Labels and Linkers), which permits addition of any label to any site on any target. The main principle in the program is to break the molecular system into a "label," a "linker," and a "target." The user can upload a "label" with any chemistry, define a "linker" based on a SMILES-like string, and then define the "target" site. The flexibility of ALLNOX facilitates theoretical evaluation of labels prior to synthesis and accommodates evaluation of experimental data in biochemical complexes containing multiple molecular types.
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Kegulian NC, Sankhagowit S, Apostolidou M, Jayasinghe SA, Malmstadt N, Butler PC, Langen R. Membrane Curvature-sensing and Curvature-inducing Activity of Islet Amyloid Polypeptide and Its Implications for Membrane Disruption. J Biol Chem 2015; 290:25782-93. [PMID: 26283787 DOI: 10.1074/jbc.m115.659797] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Indexed: 11/06/2022] Open
Abstract
Islet amyloid polypeptide (IAPP) is a 37-amino acid amyloid protein intimately associated with pancreatic islet β-cell dysfunction and death in type II diabetes. In this study, we combine spectroscopic methods and microscopy to investigate α-helical IAPP-membrane interactions. Using light scattering and fluorescence microscopy, we observe that larger vesicles become smaller upon treatment with human or rat IAPP. Electron microscopy shows the formation of various highly curved structures such as tubules or smaller vesicles in a membrane-remodeling process, and spectrofluorometric detection of vesicle leakage shows disruption of membrane integrity. This effect is stronger for human IAPP than for the less toxic rat IAPP. From CD spectra in the presence of different-sized vesicles, we also uncover the membrane curvature-sensing ability of IAPP and find that it transitions from inducing to sensing membrane curvature when lipid negative charge is decreased. Our in vivo EM images of immunogold-labeled rat IAPP and human IAPP show both forms to localize to mitochondrial cristae, which contain not only locally curved membranes but also phosphatidylethanolamine and cardiolipin, lipids with high spontaneous negative curvature. Disruption of membrane integrity by induction of membrane curvature could apply more broadly to other amyloid proteins and be responsible for membrane damage observed in other amyloid diseases as well.
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Isas JM, Langen R, Siemer AB. Solid-State Nuclear Magnetic Resonance on the Static and Dynamic Domains of Huntingtin Exon-1 Fibrils. Biochemistry 2015; 54:3942-9. [PMID: 26020223 DOI: 10.1021/acs.biochem.5b00281] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Amyloid-like fibrils formed by huntingtin exon-1 (htt_ex1) are a hallmark of Huntington's disease (HD). The structure of these fibrils is unknown, and determining their structure is an important step toward understanding the misfolding processes that cause HD. In HD, a polyglutamine (polyQ) domain in htt_ex1 is expanded to a degree that it gains the ability to form aggregates comprising the core of the resulting fibrils. Despite the simplicity of this polyQ sequence, the structure of htt_ex1 fibrils has been difficult to determine. This study provides a detailed structural investigation of fibrils formed by htt_ex1 using solid-state nuclear magnetic resonance (NMR) spectroscopy. We show that the polyQ domain of htt_ex1 forms the static amyloid core similar to polyQ model peptides. The Gln residues of this domain exist in two distinct conformations that are found in separate domains or monomers but are relatively close in space. The rest of htt_ex1 is relatively dynamic on an NMR time scale, especially the proline-rich C-terminus, which we found to be in a polyproline II helical and random coil conformation. We observed a similar dynamic C-terminus in a soluble form of htt_ex1, indicating that the conformation of this part of htt_ex1 is not changed upon its aggregation into an amyloid fibril. From these data, we propose a bottlebrush model for the fibrils formed by htt_ex1. In this model, the polyQ domains form the center and the proline-rich domains the bristles of the bottlebrush.
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Darrow MC, Sergeeva OA, Isas JM, Galaz-Montoya JG, King JA, Langen R, Schmid MF, Chiu W. Structural Mechanisms of Mutant Huntingtin Aggregation Suppression by the Synthetic Chaperonin-like CCT5 Complex Explained by Cryoelectron Tomography. J Biol Chem 2015; 290:17451-61. [PMID: 25995452 DOI: 10.1074/jbc.m115.655373] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Indexed: 11/06/2022] Open
Abstract
Huntington disease, a neurodegenerative disorder characterized by functional deficits and loss of striatal neurons, is linked to an expanded and unstable CAG trinucleotide repeat in the huntingtin gene (HTT). This DNA sequence translates to a polyglutamine repeat in the protein product, leading to mutant huntingtin (mHTT) protein aggregation. The aggregation of mHTT is inhibited in vitro and in vivo by the TCP-1 ring complex (TRiC) chaperonin. Recently, a novel complex comprised of a single type of TRiC subunit has been reported to inhibit mHTT aggregation. Specifically, the purified CCT5 homo-oligomer complex, when compared with TRiC, has a similar structure, ATP use, and substrate refolding activity, and, importantly, it also inhibits mHTT aggregation. Using an aggregation suppression assay and cryoelectron tomography coupled with a novel computational classification method, we uncover the interactions between the synthetic CCT5 complex (∼ 1 MDa) and aggregates of mutant huntingtin exon 1 containing 46 glutamines (mHTTQ46-Ex1). We find that, in a similar fashion to TRiC, synthetic CCT5 complex caps mHTT fibrils at their tips and encapsulates mHTT oligomers, providing a structural description of the inhibition of mHTTQ46-Ex1 by CCT5 complex and a shared mechanism of mHTT inhibition between TRiC chaperonin and the CCT5 complex: cap and contain.
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Fodale V, Kegulian NC, Verani M, Cariulo C, Azzollini L, Petricca L, Daldin M, Boggio R, Padova A, Kuhn R, Pacifici R, Macdonald D, Schoenfeld RC, Park H, Isas JM, Langen R, Weiss A, Caricasole A. Polyglutamine- and temperature-dependent conformational rigidity in mutant huntingtin revealed by immunoassays and circular dichroism spectroscopy. PLoS One 2014; 9:e112262. [PMID: 25464275 PMCID: PMC4251833 DOI: 10.1371/journal.pone.0112262] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Accepted: 10/06/2014] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND In Huntington's disease, expansion of a CAG triplet repeat occurs in exon 1 of the huntingtin gene (HTT), resulting in a protein bearing>35 polyglutamine residues whose N-terminal fragments display a high propensity to misfold and aggregate. Recent data demonstrate that polyglutamine expansion results in conformational changes in the huntingtin protein (HTT), which likely influence its biological and biophysical properties. Developing assays to characterize and measure these conformational changes in isolated proteins and biological samples would advance the testing of novel therapeutic approaches aimed at correcting mutant HTT misfolding. Time-resolved Förster energy transfer (TR-FRET)-based assays represent high-throughput, homogeneous, sensitive immunoassays widely employed for the quantification of proteins of interest. TR-FRET is extremely sensitive to small distances and can therefore provide conformational information based on detection of exposure and relative position of epitopes present on the target protein as recognized by selective antibodies. We have previously reported TR-FRET assays to quantify HTT proteins based on the use of antibodies specific for different amino-terminal HTT epitopes. Here, we investigate the possibility of interrogating HTT protein conformation using these assays. METHODOLOGY/PRINCIPAL FINDINGS By performing TR-FRET measurements on the same samples (purified recombinant proteins or lysates from cells expressing HTT fragments or full length protein) at different temperatures, we have discovered a temperature-dependent, reversible, polyglutamine-dependent conformational change of wild type and expanded mutant HTT proteins. Circular dichroism spectroscopy confirms the temperature and polyglutamine-dependent change in HTT structure, revealing an effect of polyglutamine length and of temperature on the alpha-helical content of the protein. CONCLUSIONS/SIGNIFICANCE The temperature- and polyglutamine-dependent effects observed with TR-FRET on HTT proteins represent a simple, scalable, quantitative and sensitive assay to identify genetic and pharmacological modulators of mutant HTT conformation, and potentially to assess the relevance of conformational changes during onset and progression of Huntington's disease.
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Lai Y, Kim S, Varkey J, Lou X, Song JK, Diao J, Langen R, Shin YK. Nonaggregated α-synuclein influences SNARE-dependent vesicle docking via membrane binding. Biochemistry 2014; 53:3889-96. [PMID: 24884175 PMCID: PMC4075992 DOI: 10.1021/bi5002536] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
![]()
α-Synuclein
(α-Syn), a major component of Lewy body
that is considered as the hallmark of Parkinson’s disease (PD),
has been implicated in neuroexocytosis. Overexpression of α-Syn
decreases the neurotransmitter release. However, the mechanism by
which α-Syn buildup inhibits the neurotransmitter release is
still unclear. Here, we investigated the effect of nonaggregated α-Syn
on SNARE-dependent liposome fusion using fluorescence methods. In
ensemble in vitro assays, α-Syn reduces lipid mixing mediated
by SNAREs. Furthermore, with the more advanced single-vesicle assay
that can distinguish vesicle docking from fusion, we found that α-Syn
specifically inhibits vesicle docking, without interfering with the
fusion. The inhibition in vesicle docking requires α-Syn binding
to acidic lipid containing membranes. Thus, these results imply the
existence of at least two mechanisms of inhibition of SNARE-dependent
membrane fusion: at high concentrations, nonaggregated α-Syn
inhibits docking by binding acidic lipids but not v-SNARE; on the
other hand, at much lower concentrations, large α-Syn oligomers
inhibit via a mechanism that requires v-SNARE interaction [Choi et al. 2013, 110 (10), 4087−409223431141].
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Shah C, Hegde BG, Morén B, Behrmann E, Mielke T, Moenke G, Spahn CMT, Lundmark R, Daumke O, Langen R. Structural insights into membrane interaction and caveolar targeting of dynamin-like EHD2. Structure 2014; 22:409-420. [PMID: 24508342 DOI: 10.1016/j.str.2013.12.015] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Revised: 12/16/2013] [Accepted: 12/21/2013] [Indexed: 01/17/2023]
Abstract
The dynamin-related Eps15-homology domain-containing protein 2 (EHD2) is a membrane-remodeling ATPase that regulates the dynamics of caveolae. Here, we established an electron paramagnetic resonance (EPR) approach to characterize structural features of membrane-bound EHD2. We show that residues at the tip of the helical domain can insert into the membrane and may create membrane curvature by a wedging mechanism. Using EPR and X-ray crystallography, we found that the N terminus is folded into a hydrophobic pocket of the GTPase domain in solution and can be released into the membrane. Cryoelectron microscopy demonstrated that the N terminus is not essential for oligomerization of EHD2 into a membrane-anchored scaffold. Instead, we found a function of the N terminus in regulating targeting and stable association of EHD2 to caveolae. Our data uncover an unexpected, membrane-induced regulatory switch in EHD2 and demonstrate the versatility of EPR to study structure and function of dynamin superfamily proteins.
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Varkey J, Mizuno N, Hegde BG, Cheng N, Steven AC, Langen R. α-Synuclein oligomers with broken helical conformation form lipoprotein nanoparticles. J Biol Chem 2013; 288:17620-30. [PMID: 23609437 DOI: 10.1074/jbc.m113.476697] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
α-Synuclein (αS) is a membrane-binding protein with sequence similarity to apolipoproteins and other lipid-carrying proteins, which are capable of forming lipid-containing nanoparticles, sometimes referred to as "discs." Previously, it has been unclear whether αS also possesses this property. Using cryo-electron microscopy and light scattering, we found that αS can remodel phosphatidylglycerol vesicles into nanoparticles whose shape (ellipsoidal) and dimensions (in the 7-10-nm range) resemble those formed by apolipoproteins. The molar ratio of αS to lipid in nanoparticles is ∼1:20, and αS is oligomeric (including trimers and tetramers). Similar nanoparticles form when αS is added to vesicles of mitochondrial lipids. This observation suggests a mechanism for the previously reported disruption of mitochondrial membranes by αS. Circular dichroism and four-pulse double electron electron resonance experiments revealed that in nanoparticles αS assumes a broken helical conformation distinct from the extended helical conformation adopted when αS is bound to intact vesicles or membrane tubules. We also observed αS-dependent tubule and nanoparticle formation in the presence of oleic acid, implying that αS can interact with fatty acids and lipids in a similar manner. αS-related nanoparticles might play a role in lipid and fatty acid transport functions previously attributed to this protein.
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Abstract
The islet in type 2 diabetes (T2DM) is characterized by a deficit in β-cells, increased β-cell apoptosis, and extracellular amyloid deposits derived from islet amyloid polypeptide (IAPP). In the absence of longitudinal studies, it is unknown if the low β-cell mass in T2DM precedes diabetes onset (is a risk factor for diabetes) or develops as a consequence of the disease process. Although insulin resistance is a risk factor for T2DM, most individuals who are insulin resistant do not develop diabetes. By inference, an increased β-cell workload results in T2DM in some but not all individuals. We propose that the extent of the β-cell mass that develops during childhood may underlie subsequent successful or failed adaptation to insulin resistance in later life. We propose that a low innate β-cell mass in the face of subsequent insulin resistance may expose β-cells to a burden of insulin and IAPP biosynthetic demand that exceeds the cellular capacity for protein folding and trafficking. If this threshold is crossed, intracellular toxic IAPP membrane permeant oligomers (cylindrins) may form, compromising β-cell function and inducing β-cell apoptosis.
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Cheng CY, Varkey J, Langen R, Han S. Hydration Dynamics as a Molecular Ruler for Refining Protein Structure at Lipid Membrane Interfaces. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.1246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Li Y, Hatmal MM, Langen R, Haworth IS. Idealized models of protofilaments of human islet amyloid polypeptide. J Chem Inf Model 2012; 52:2983-91. [PMID: 23116372 DOI: 10.1021/ci300300e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Fibrils formed by assembly of human islet amyloid polypeptide (hIAPP) are found in most patients with type II diabetes. Structurally, these fibrils are composed of multiple protofilaments and are characterized by extended beta sheets, variable helical twists, and different morphologies. We have previously derived models for the hIAPP protofilament using simulations constrained by data from EPR spectroscopy. In the current work, these models were used as a basis for generating idealized hIAPP protofilaments with symmetrical geometrical properties using a new algorithm, MFIBRIL. We show good agreement of the idealized protofilaments with experimental data for amino acid side chain orientations and geometrical features including the inter-β sheet distance and the protofilament radius. These idealized protofilaments can be used in MFIBRIL to generate fibril models that may be experimentally testable at the molecular level. MFIBRIL can also be used for building structures of any repetitive molecular assembly starting with a single building block obtained from any source.
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Lai CL, Jao CC, Lyman E, Gallop JL, Peter BJ, McMahon HT, Langen R, Voth GA. Membrane binding and self-association of the epsin N-terminal homology domain. J Mol Biol 2012; 423:800-17. [PMID: 22922484 PMCID: PMC3682188 DOI: 10.1016/j.jmb.2012.08.010] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Revised: 08/13/2012] [Accepted: 08/16/2012] [Indexed: 01/23/2023]
Abstract
Epsin possesses a conserved epsin N-terminal homology (ENTH) domain that acts as a phosphatidylinositol 4,5-bisphosphate‐lipid‐targeting and membrane‐curvature‐generating element. Upon binding phosphatidylinositol 4,5‐bisphosphate, the N-terminal helix (H0) of the ENTH domain becomes structured and aids in the aggregation of ENTH domains, which results in extensive membrane remodeling. In this article, atomistic and coarse-grained (CG) molecular dynamics (MD) simulations are used to investigate the structure and the stability of ENTH domain aggregates on lipid bilayers. EPR experiments are also reported for systems composed of different ENTH-bound membrane morphologies, including membrane vesicles as well as preformed membrane tubules. The EPR data are used to help develop a molecular model of ENTH domain aggregates on preformed lipid tubules that are then studied by CG MD simulation. The combined computational and experimental approach suggests that ENTH domains exist predominantly as monomers on vesiculated structures, while ENTH domains self-associate into dimeric structures and even higher‐order oligomers on the membrane tubes. The results emphasize that the arrangement of ENTH domain aggregates depends strongly on whether the local membrane curvature is isotropic or anisotropic. The molecular mechanism of ENTH‐domain-induced membrane vesiculation and tubulation and the implications of the epsin's role in clathrin-mediated endocytosis resulting from the interplay between ENTH domain membrane binding and ENTH domain self-association are also discussed.
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Woodham AW, Da Silva DM, Skeate JG, Raff AB, Ambroso MR, Brand HE, Isas JM, Langen R, Kast WM. The S100A10 subunit of the annexin A2 heterotetramer facilitates L2-mediated human papillomavirus infection. PLoS One 2012; 7:e43519. [PMID: 22927980 PMCID: PMC3425544 DOI: 10.1371/journal.pone.0043519] [Citation(s) in RCA: 116] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Accepted: 07/23/2012] [Indexed: 12/13/2022] Open
Abstract
Mucosotropic, high-risk human papillomaviruses (HPV) are sexually transmitted viruses that are causally associated with the development of cervical cancer. The most common high-risk genotype, HPV16, is an obligatory intracellular virus that must gain entry into host epithelial cells and deliver its double stranded DNA to the nucleus. HPV capsid proteins play a vital role in these steps. Despite the critical nature of these capsid protein-host cell interactions, the precise cellular components necessary for HPV16 infection of epithelial cells remains unknown. Several neutralizing epitopes have been identified for the HPV16 L2 minor capsid protein that can inhibit infection after initial attachment of the virus to the cell surface, which suggests an L2-specific secondary receptor or cofactor is required for infection, but so far no specific L2-receptor has been identified. Here, we demonstrate that the annexin A2 heterotetramer (A2t) contributes to HPV16 infection and co-immunoprecipitates with HPV16 particles on the surface of epithelial cells in an L2-dependent manner. Inhibiting A2t with an endogenous annexin A2 ligand, secretory leukocyte protease inhibitor (SLPI), or with an annexin A2 antibody significantly reduces HPV16 infection. With electron paramagnetic resonance, we demonstrate that a previously identified neutralizing epitope of L2 (aa 108-120) specifically interacts with the S100A10 subunit of A2t. Additionally, mutation of this L2 region significantly reduces binding to A2t and HPV16 pseudovirus infection. Furthermore, downregulation of A2t with shRNA significantly decreases capsid internalization and infection by HPV16. Taken together, these findings indicate that A2t contributes to HPV16 internalization and infection of epithelial cells and this interaction is dependent on the presence of the L2 minor capsid protein.
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44
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Bugg CW, Isas JM, Fischer T, Patterson PH, Langen R. Structural features and domain organization of huntingtin fibrils. J Biol Chem 2012; 287:31739-46. [PMID: 22801429 DOI: 10.1074/jbc.m112.353839] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Misfolding and aggregation of huntingtin is one of the hallmarks of Huntington disease, but the overall structure of these aggregates and the mechanisms by which huntingtin misfolds remain poorly understood. Here we used site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy to study the structural features of huntingtin exon 1 (HDx1) containing 46 glutamine residues in its polyglutamine (polyQ) region. Despite some residual structuring in the N terminus, we find that soluble HDx1 is highly dynamic. Upon aggregation, the polyQ domain becomes strongly immobilized indicating significant tertiary or quaternary packing interactions. Analysis of spin-spin interactions does not show the close contact between same residues that is characteristic of the parallel, in-register structure commonly found in amyloids. Nevertheless, the same residues are still within 20 Å of each other, suggesting that polyQ domains from different molecules come into proximity in the fibrils. The N terminus has previously been found to take up a helical structure in fibrils. We find that this domain not only becomes structured, but that it also engages in tertiary or quaternary packing interactions. The existence of spin-spin interactions in this region suggests that such contacts could be made between N-terminal domains from different molecules. In contrast, the C-terminal domain is dynamic, contains polyproline II structure, and lacks pronounced packing interactions. This region must be facing away from the core of the fibrils. Collectively, these data provide new constraints for building structural models of HDx1 fibrils.
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45
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Mizuno N, Varkey J, Kegulian NC, Hegde BG, Cheng N, Langen R, Steven AC. Remodeling of lipid vesicles into cylindrical micelles by α-synuclein in an extended α-helical conformation. J Biol Chem 2012; 287:29301-11. [PMID: 22767608 DOI: 10.1074/jbc.m112.365817] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
α-Synuclein (αS) is a protein with multiple conformations and interactions. Natively unfolded in solution, αS accumulates as amyloid in neurological tissue in Parkinson disease and interacts with membranes under both physiological and pathological conditions. Here, we used cryoelectron microscopy in conjunction with electron paramagnetic resonance (EPR) and other techniques to characterize the ability of αS to remodel vesicles. At molar ratios of 1:5 to 1:40 for protein/lipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol), large spherical vesicles are converted into cylindrical micelles ~50 Å in diameter. Other lipids of the same charge (negative) exhibit generally similar behavior, although bilayer tubes of 150-500 Å in width are also produced, depending on the lipid acyl chains. At higher protein/lipid ratios, discoid particles, 70-100 Å across, are formed. EPR data show that, on cylindrical micelles, αS adopts an extended amphipathic α-helical conformation, with its long axis aligned with the tube axis. The observed geometrical relationship between αS and the micelle suggests that the wedging of its long α-helix into the outer leaflet of a membrane may cause curvature and an anisotropic partition of lipids, leading to tube formation.
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46
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Meier F, Abeywardana T, Dhall A, Marotta NP, Varkey J, Langen R, Chatterjee C, Pratt MR. Semisynthetic, site-specific ubiquitin modification of α-synuclein reveals differential effects on aggregation. J Am Chem Soc 2012; 134:5468-71. [PMID: 22404520 DOI: 10.1021/ja300094r] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The process of neurodegeneration in Parkinson's Disease is intimately associated with the aggregation of the protein α-synuclein into toxic oligomers and fibrils. Interestingly, many of these protein aggregates are found to be post-translationally modified by ubiquitin at several different lysine residues. However, the inability to generate homogeneously ubiquitin modified α-synuclein at each site has prevented the understanding of the specific biochemical consequences. We have used protein semisynthesis to generate nine site-specifically ubiquitin modified α-synuclein derivatives and have demonstrated that different ubiquitination sites have differential effects on α-synuclein aggregation.
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47
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Krishnamani V, Hegde BG, Langen R, Lanyi JK. Secondary and Tertiary Structure of Bacteriorhodopsin in the SDS Denatured State. Biochemistry 2012; 51:1051-60. [DOI: 10.1021/bi201769z] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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48
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Hatmal MM, Li Y, Hegde BG, Hegde PB, Jao CC, Langen R, Haworth IS. Computer modeling of nitroxide spin labels on proteins. Biopolymers 2012; 97:35-44. [PMID: 21792846 PMCID: PMC3422567 DOI: 10.1002/bip.21699] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 06/24/2011] [Accepted: 06/25/2011] [Indexed: 01/26/2023]
Abstract
Electron paramagnetic resonance using site-directed spin labeling can be used as an approach for determination of protein structures that are difficult to solve by other methods. One important aspect of this approach is the measurement of interlabel distances using the double electron-electron resonance (DEER) method. Interpretation of experimental data could be facilitated by a computational approach to calculation of interlabel distances. We describe an algorithm, PRONOX, for rapid computation of interlabel distances based on calculation of spin label conformer distributions at any site of a protein. The program incorporates features of the label distribution established experimentally, including weighting of favorable conformers of the label. Distances calculated by PRONOX were compared with new DEER distances for amphiphysin and annexin B12 and with published data for FCHo2 (F-BAR), endophilin, and α-synuclein, a total of 44 interlabel distances. The program reproduced these distances accurately (r(2) = 0.94, slope = 0.98). For 9 of the 11 distances for amphiphysin, PRONOX reproduced the experimental data to within 2.5 Å. The speed and accuracy of PRONOX suggest that the algorithm can be used for fitting to DEER data for determination of protein tertiary structure.
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Bedrood S, Li Y, Isas JM, Hegde BG, Baxa U, Haworth IS, Langen R. Fibril structure of human islet amyloid polypeptide. J Biol Chem 2011; 287:5235-41. [PMID: 22187437 DOI: 10.1074/jbc.m111.327817] [Citation(s) in RCA: 133] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Misfolding and amyloid fibril formation by human islet amyloid polypeptide (hIAPP) are thought to be important in the pathogenesis of type 2 diabetes, but the structures of the misfolded forms remain poorly understood. Here we developed an approach that combines site-directed spin labeling with continuous wave and pulsed EPR to investigate local secondary structure and to determine the relative orientation of the secondary structure elements with respect to each other. These data indicated that individual hIAPP molecules take up a hairpin fold within the fibril. This fold contains two β-strands that are much farther apart than expected from previous models. Atomistic structural models were obtained using computational refinement with EPR data as constraints. The resulting family of structures exhibited a left-handed helical twist, in agreement with the twisted morphology observed by electron microscopy. The fibril protofilaments contain stacked hIAPP monomers that form opposing β-sheets that twist around each other. The two β-strands of the monomer adopt out-of-plane positions and are staggered by about three peptide layers (∼15 Å). These results provide a mechanism for hIAPP fibril formation and could explain the remarkable stability of the fibrils. Thus, the structural model serves as a starting point for understanding and preventing hIAPP misfolding.
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Jensen MB, Bhatia VK, Jao CC, Rasmussen JE, Pedersen SL, Jensen KJ, Langen R, Stamou D. Membrane curvature sensing by amphipathic helices: a single liposome study using α-synuclein and annexin B12. J Biol Chem 2011; 286:42603-42614. [PMID: 21953452 DOI: 10.1074/jbc.m111.271130] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Preferential binding of proteins on curved membranes (membrane curvature sensing) is increasingly emerging as a general mechanism whereby cells may effect protein localization and trafficking. Here we use a novel single liposome fluorescence microscopy assay to examine a common sensing motif, the amphipathic helix (AH), and provide quantitative measures describing and distinguishing membrane binding and sensing behavior. By studying two AH-containing proteins, α-synuclein and annexin B12, as well as a range of AH peptide mutants, we reveal that both the hydrophobic and hydrophilic faces of the helix greatly influence binding and sensing. Although increased hydrophobic and electrostatic interactions with the membrane both lead to greater densities of bound protein, the former yields membrane curvature-sensitive binding, whereas the latter is not curvature-dependent. However, the relative contributions of both components determine the sensing of AHs. In contrast, charge density in the lipid membrane seems important primarily in attracting AHs to the membrane but does not significantly influence sensing. These observations were made possible by the ability of our assay to distinguish within our samples liposomes with and without bound protein as well as the density of bound protein. Our findings suggest that the description of membrane curvature-sensing requires consideration of several factors such as short and long range electrostatic interactions, hydrogen bonding, and the volume and structure of inserted hydrophobic residues.
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