1
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Yoon J, Zhang YM, Her C, Grant RA, Ponomarenko AI, Ackermann BE, Hui T, Lin YS, Debelouchina GT, Shoulders MD. The immune-evasive proline-283 substitution in influenza nucleoprotein increases aggregation propensity without altering the native structure. Sci Adv 2024; 10:eadl6144. [PMID: 38640233 PMCID: PMC11029814 DOI: 10.1126/sciadv.adl6144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 03/15/2024] [Indexed: 04/21/2024]
Abstract
Nucleoprotein (NP) is a key structural protein of influenza ribonucleoprotein complexes and is central to viral RNA packing and trafficking. NP also determines the sensitivity of influenza to myxovirus resistance protein 1 (MxA), an innate immunity factor that restricts influenza replication. A few critical MxA-resistant mutations have been identified in NP, including the highly conserved proline-283 substitution. This essential proline-283 substitution impairs influenza growth, a fitness defect that becomes particularly prominent at febrile temperature (39°C) when host chaperones are depleted. Here, we biophysically characterize proline-283 NP and serine-283 NP to test whether the fitness defect is caused by the proline-283 substitution introducing folding defects. We show that the proline-283 substitution changes the folding pathway of NP, making NP more aggregation prone during folding, but does not alter the native structure of the protein. These findings suggest that influenza has evolved to hijack host chaperones to promote the folding of otherwise biophysically incompetent viral proteins that enable innate immune system escape.
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Affiliation(s)
- Jimin Yoon
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Yu Meng Zhang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Cheenou Her
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA
| | - Robert A. Grant
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Anna I. Ponomarenko
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Bryce E. Ackermann
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA
| | - Tiffani Hui
- Department of Chemistry, Tufts University, Medford, MA, USA
| | - Yu-Shan Lin
- Department of Chemistry, Tufts University, Medford, MA, USA
| | - Galia T. Debelouchina
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA
| | - Matthew D. Shoulders
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
- Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, USA
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2
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Phan TM, Kim YC, Debelouchina GT, Mittal J. Interplay between charge distribution and DNA in shaping HP1 paralog phase separation and localization. eLife 2024; 12:RP90820. [PMID: 38592759 PMCID: PMC11003746 DOI: 10.7554/elife.90820] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/10/2024] Open
Abstract
The heterochromatin protein 1 (HP1) family is a crucial component of heterochromatin with diverse functions in gene regulation, cell cycle control, and cell differentiation. In humans, there are three paralogs, HP1α, HP1β, and HP1γ, which exhibit remarkable similarities in their domain architecture and sequence properties. Nevertheless, these paralogs display distinct behaviors in liquid-liquid phase separation (LLPS), a process linked to heterochromatin formation. Here, we employ a coarse-grained simulation framework to uncover the sequence features responsible for the observed differences in LLPS. We highlight the significance of the net charge and charge patterning along the sequence in governing paralog LLPS propensities. We also show that both highly conserved folded and less-conserved disordered domains contribute to the observed differences. Furthermore, we explore the potential co-localization of different HP1 paralogs in multicomponent assemblies and the impact of DNA on this process. Importantly, our study reveals that DNA can significantly reshape the stability of a minimal condensate formed by HP1 paralogs due to competitive interactions of HP1α with HP1β and HP1γ versus DNA. In conclusion, our work highlights the physicochemical nature of interactions that govern the distinct phase-separation behaviors of HP1 paralogs and provides a molecular framework for understanding their role in chromatin organization.
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Affiliation(s)
- Tien M Phan
- Artie McFerrin Department of Chemical Engineering, Texas A&M UniversityCollege StationUnited States
| | - Young C Kim
- Center for Materials Physics and Technology, Naval Research LaboratoryWashingtonUnited States
| | - Galia T Debelouchina
- Department of Chemistry and Biochemistry, University of California, San DiegoLa JollaUnited States
| | - Jeetain Mittal
- Artie McFerrin Department of Chemical Engineering, Texas A&M UniversityCollege StationUnited States
- Department of Chemistry, Texas A&M UniversityCollege StationUnited States
- Interdisciplinary Graduate Program in Genetics and Genomics, Texas A&M UniversityCollege StationUnited States
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3
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Abasi LS, Elathram N, Movva M, Deep A, Corbett KD, Debelouchina GT. Phosphorylation regulates tau's phase separation behavior and interactions with chromatin. Commun Biol 2024; 7:251. [PMID: 38429335 PMCID: PMC10907630 DOI: 10.1038/s42003-024-05920-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Accepted: 02/16/2024] [Indexed: 03/03/2024] Open
Abstract
Tau is a microtubule-associated protein often found in neurofibrillary tangles (NFTs) in the brains of patients with Alzheimer's disease. Beyond this context, mounting evidence suggests that tau localizes into the nucleus, where it may play a role in DNA protection and heterochromatin regulation. The molecular mechanisms behind these observations are currently unclear. Using in vitro biophysical experiments, here we demonstrate that tau can undergo liquid-liquid phase separation (LLPS) with DNA, mononucleosomes, and reconstituted nucleosome arrays under low salt conditions. Low concentrations of tau promote chromatin compaction and protect DNA from digestion. While the material state of samples at physiological salt is dominated by chromatin oligomerization, tau can still associate strongly and reversibly with nucleosome arrays. These properties are driven by tau's strong interactions with linker and nucleosomal DNA. In addition, tau co-localizes into droplets formed by nucleosome arrays and phosphorylated HP1α, a key heterochromatin constituent thought to function through an LLPS mechanism. Importantly, LLPS and chromatin interactions are disrupted by aberrant tau hyperphosphorylation. These biophysical properties suggest that tau may directly impact DNA and chromatin accessibility and that loss of these interactions could contribute to the aberrant nuclear effects seen in tau pathology.
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Affiliation(s)
- Lannah S Abasi
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093, USA
| | - Nesreen Elathram
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093, USA
| | - Manasi Movva
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093, USA
| | - Amar Deep
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, 92093, USA
| | - Kevin D Corbett
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, 92093, USA
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, 92093, USA
| | - Galia T Debelouchina
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093, USA.
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4
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Abasi LS, Elathram N, Movva M, Deep A, Corbett KD, Debelouchina GT. Phosphorylation regulates tau's phase separation behavior and interactions with chromatin. bioRxiv 2023:2023.12.21.572911. [PMID: 38187700 PMCID: PMC10769318 DOI: 10.1101/2023.12.21.572911] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
Tau is a microtubule-associated protein often found in neurofibrillary tangles (NFTs) in the brains of patients with Alzheimer's disease (AD). Beyond this context, mounting evidence suggests that tau localizes into the nucleus, where it may play a role in DNA protection and heterochromatin regulation. Models of tau depletion or pathology show loss of genetically silent heterochromatin, aberrant expression of heterochromatic genes, and transposable element activation. The molecular mechanisms behind these observations are currently unclear. Using in vitro biophysical experiments, here we demonstrate that tau can undergo liquid-liquid phase separation (LLPS) with DNA, mononucleosomes, and reconstituted nucleosome arrays under low salt conditions. Low concentrations of tau promote chromatin compaction and protect DNA from digestion. While the material state of samples at physiological salt is dominated by chromatin oligomerization, tau can still associate strongly and reversibly with nucleosome arrays. These properties are driven by tau's strong interactions with linker and nucleosomal DNA, while magic angle spinning (MAS) solid-state NMR experiments show that tau binding does not drastically alter nucleosome structure and dynamics. In addition, tau co-localizes into droplets formed by nucleosome arrays and phosphorylated HP1α, a key heterochromatin constituent thought to function through an LLPS mechanism. Importantly, LLPS and chromatin interactions are disrupted by aberrant tau hyperphosphorylation. These biophysical properties suggest that tau may directly impact DNA and chromatin accessibility and that loss of these interactions could contribute to the aberrant nuclear effects seen in tau pathology.
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Affiliation(s)
- Lannah S. Abasi
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
| | - Nesreen Elathram
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
| | - Manasi Movva
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
| | - Amar Deep
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA
| | - Kevin D. Corbett
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA
| | - Galia T. Debelouchina
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
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5
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Phan TM, Kim YC, Debelouchina GT, Mittal J. Interplay between charge distribution and DNA in shaping HP1 paralog phase separation and localization. bioRxiv 2023:2023.05.28.542535. [PMID: 37398008 PMCID: PMC10312469 DOI: 10.1101/2023.05.28.542535] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/04/2023]
Abstract
The heterochromatin protein 1 (HP1) family is a crucial component of heterochromatin with diverse functions in gene regulation, cell cycle control, and cell differentiation. In humans, there are three paralogs, HP1α, HP1β, and HP1γ, which exhibit remarkable similarities in their domain architecture and sequence properties. Nevertheless, these paralogs display distinct behaviors in liquid-liquid phase separation (LLPS), a process linked to heterochromatin formation. Here, we employ a coarse-grained simulation framework to uncover the sequence features responsible for the observed differences in LLPS. We highlight the significance of the net charge and charge patterning along the sequence in governing paralog LLPS propensities. We also show that both highly conserved folded and less-conserved disordered domains contribute to the observed differences. Furthermore, we explore the potential co-localization of different HP1 paralogs in multicomponent assemblies and the impact of DNA on this process. Importantly, our study reveals that DNA can significantly reshape the stability of a minimal condensate formed by HP1 paralogs due to competitive interactions of HP1α with HP1β and HP1γ versus DNA. In conclusion, our work highlights the physicochemical nature of interactions that govern the distinct phase-separation behaviors of HP1 paralogs and provides a molecular framework for understanding their role in chromatin organization.
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Affiliation(s)
- Tien M. Phan
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX, USA
| | - Young C. Kim
- Center for Materials Physics and Technology, Naval Research Laboratory, Washington, DC, USA
| | - Galia T. Debelouchina
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, USA
| | - Jeetain Mittal
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX, USA
- Department of Chemistry, Texas A&M University, College Station, TX, USA
- Interdisciplinary Graduate Program in Genetics and Genomics, Texas A&M University, College Station, TX, USA
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6
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Elathram N, Ackermann BE, Clark ET, Dunn SR, Debelouchina GT. Phosphorylated HP1α-Nucleosome Interactions in Phase Separated Environments. J Am Chem Soc 2023; 145:23994-24004. [PMID: 37870432 PMCID: PMC10636758 DOI: 10.1021/jacs.3c06481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Revised: 10/03/2023] [Accepted: 10/05/2023] [Indexed: 10/24/2023]
Abstract
In the nucleus, transcriptionally silent genes are sequestered into heterochromatin compartments comprising nucleosomes decorated with histone H3 Lys9 trimethylation and a protein called HP1α. This protein can form liquid-liquid droplets in vitro and potentially organize heterochromatin through a phase separation mechanism that is promoted by phosphorylation. Elucidating the molecular interactions that drive HP1α phase separation and its consequences on nucleosome structure and dynamics has been challenging due to the viscous and heterogeneous nature of such assemblies. Here, we tackle this problem by a combination of solution and solid-state NMR spectroscopy, which allows us to dissect the interactions of phosphorylated HP1α with nucleosomes in the context of phase separation. Our experiments indicate that phosphorylated human HP1α does not cause any major rearrangements to the nucleosome core, in contrast to the yeast homologue Swi6. Instead, HP1α interacts specifically with the methylated H3 tails and slows the dynamics of the H4 tails. Our results shed light on how phosphorylated HP1α proteins may regulate the heterochromatin landscape, while our approach provides an atomic resolution view of a heterogeneous and dynamic biological system regulated by a complex network of interactions and post-translational modifications.
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Affiliation(s)
- Nesreen Elathram
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
| | - Bryce E. Ackermann
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
| | - Evan T. Clark
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
| | - Shelby R. Dunn
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
| | - Galia T. Debelouchina
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
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7
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Yoon J, Zhang YM, Her C, Grant RA, Ponomarenko AM, Ackermann BE, Debelouchina GT, Shoulders MD. The Immune-Evasive Proline 283 Substitution in Influenza Nucleoprotein Increases Aggregation Propensity Without Altering the Native Structure. bioRxiv 2023:2023.09.08.556894. [PMID: 37745335 PMCID: PMC10515774 DOI: 10.1101/2023.09.08.556894] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/26/2023]
Abstract
Nucleoprotein (NP) is a key structural protein of influenza ribonucleoprotein complexes and is central to viral RNA packing and trafficking. In human cells, the interferon induced Myxovirus resistance protein 1 (MxA) binds to NP and restricts influenza replication. This selection pressure has caused NP to evolve a few critical MxA-resistant mutations, particularly the highly conserved Pro283 substitution. Previous work showed that this essential Pro283 substitution impairs influenza growth, and the fitness defect becomes particularly prominent at febrile temperature (39 °C) when host chaperones are depleted. Here, we biophysically characterize Pro283 NP and Ser283 NP to test if the fitness defect is owing to Pro283 substitution introducing folding defects. We show that the Pro283 substitution changes the folding pathway of NP without altering the native structure, making NP more aggregation prone during folding. These findings suggest that influenza has evolved to hijack host chaperones to promote the folding of otherwise biophysically incompetent viral proteins that enable innate immune system escape. Teaser Pro283 substitution in flu nucleoprotein introduces folding defects, and makes influenza uniquely dependent on host chaperones.
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8
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Kent JE, Ackermann BE, Debelouchina GT, Marassi FM. Dynamic Nuclear Polarization Illuminates Key Protein-Lipid Interactions in the Native Bacterial Cell Envelope. Biochemistry 2023; 62:2252-2256. [PMID: 37459255 PMCID: PMC11019665 DOI: 10.1021/acs.biochem.3c00262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/28/2023]
Abstract
Elucidating the structure and interactions of proteins in native environments is a fundamental goal of structural biology. Nuclear magnetic resonance (NMR) spectroscopy is well suited for this task but often suffers from low sensitivity, especially in complex biological settings. Here, we use a sensitivity-enhancement technique called dynamic nuclear polarization (DNP) to overcome this challenge. We apply DNP to capture the membrane interactions of the outer membrane protein Ail, a key component of the host invasion pathway of Yersinia pestis. We show that the DNP-enhanced NMR spectra of Ail in native bacterial cell envelopes are well resolved and enriched in correlations that are invisible in conventional solid-state NMR experiments. Furthermore, we demonstrate the ability of DNP to capture elusive interactions between the protein and the surrounding lipopolysaccharide layer. Our results support a model where the extracellular loop arginine residues remodel the membrane environment, a process that is crucial for host invasion and pathogenesis.
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Affiliation(s)
- James E Kent
- Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037, United States
| | - Bryce E Ackermann
- Department Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, United States
| | - Galia T Debelouchina
- Department Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, United States
| | - Francesca M Marassi
- Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037, United States
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226-3548, United States
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9
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Kent JE, Ackermann BE, Debelouchina GT, Marassi FM. Dynamic nuclear polarization illuminates key protein-lipid interactions in the native bacterial cell envelope. bioRxiv 2023:2023.05.18.541325. [PMID: 37292594 PMCID: PMC10245764 DOI: 10.1101/2023.05.18.541325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Elucidating the structure and interactions of proteins in native environments has become a fundamental goal of structural biology. Nuclear magnetic resonance (NMR) spectroscopy is well suited for this task but often suffers from low sensitivity, especially in complex biological settings. Here, we use a sensitivity-enhancement technique called dynamic nuclear polarization (DNP) to overcome this challenge. We apply DNP to capture the membrane interactions of the outer membrane protein Ail, a key component of the host invasion pathway of Yersinia pestis . We show that the DNP-enhanced NMR spectra of Ail in native bacterial cell envelopes are well resolved and enriched in correlations that are invisible in conventional solid-state NMR experiments. Furthermore, we demonstrate the ability of DNP to capture elusive interactions between the protein and the surrounding lipopolysaccharide layer. Our results support a model where the extracellular loop arginine residues remodel the membrane environment, a process that is crucial for host invasion and pathogenesis.
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10
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Abasi L, Elathram N, Movva M, Debelouchina GT. Investigations into the phase separation and nuclear role of tau. Biophys J 2023; 122:487a. [PMID: 36784506 DOI: 10.1016/j.bpj.2022.11.2603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2023] Open
Affiliation(s)
- Lannah Abasi
- University of California San Diego, La Jolla, CA, USA
| | - Nesreen Elathram
- Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, USA
| | - Manasi Movva
- University of California San Diego, La Jolla, CA, USA
| | - Galia T Debelouchina
- Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, USA
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11
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Ackermann BE, Lim BJ, Elathram N, Narayanan S, Debelouchina GT. A Comparative Study of Nitroxide-Based Biradicals for Dynamic Nuclear Polarization in Cellular Environments. Chembiochem 2022; 23:e202200577. [PMID: 36250276 PMCID: PMC9856215 DOI: 10.1002/cbic.202200577] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Revised: 10/15/2022] [Indexed: 01/25/2023]
Abstract
Dynamic nuclear polarization (DNP) is a powerful tool to enhance the NMR signals of molecules by transferring polarization from unpaired electron spins to nuclei through microwave irradiation. The resulting signal enhancements can enable the analysis of samples that have previously been intractable by NMR spectroscopy, including proteins, nucleic acids, and metabolites in cells. To carry out DNP, the sample is doped with a polarization agent, a biradical containing two nitroxide moieties. DNP applications in cells, however, present significant challenges as nitroxides are often susceptible to the reducing cellular environment. Here, we introduce a novel polarization agent, POPAPOL, that exhibits increased lifetimes under reducing conditions. We also compare its bioresistance and DNP performance with three popular, commercially available polarization agents. Our work indicates that pyrrolidine-based nitroxides can outperform piperidine-based nitroxides in cellular environments, and that future polarization agent designs must carefully balance DNP performance and stability for cellular applications.
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Affiliation(s)
- Bryce E. Ackermann
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
| | - Byung Joon Lim
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
| | - Nesreen Elathram
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
| | - Sirish Narayanan
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
| | - Galia T. Debelouchina
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA,Corresponding author: , http://debelouchinalab.ucsd.edu/
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12
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Berkeley RF, Debelouchina GT. Chemical tools for study and modulation of biomolecular phase transitions. Chem Sci 2022; 13:14226-14245. [PMID: 36545140 PMCID: PMC9749140 DOI: 10.1039/d2sc04907d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2022] [Accepted: 11/21/2022] [Indexed: 11/23/2022] Open
Abstract
Biomolecular phase transitions play an important role in organizing cellular processes in space and time. Methods and tools for studying these transitions, and the intrinsically disordered proteins (IDPs) that often drive them, are typically less developed than tools for studying their folded protein counterparts. In this perspective, we assess the current landscape of chemical tools for studying IDPs, with a specific focus on protein liquid-liquid phase separation (LLPS). We highlight methodologies that enable imaging and spectroscopic studies of these systems, including site-specific labeling with small molecules and the diverse range of capabilities offered by inteins and protein semisynthesis. We discuss strategies for introducing post-translational modifications that are central to IDP and LLPS function and regulation. We also investigate the nascent field of noncovalent small-molecule modulators of LLPS. We hope that this review of the state-of-the-art in chemical tools for interrogating IDPs and LLPS, along with an associated perspective on areas of unmet need, can serve as a valuable and timely resource for these rapidly expanding fields of study.
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Affiliation(s)
- Raymond F. Berkeley
- Department of Chemistry and Biochemistry, University of California San DiegoLa JollaCAUSA
| | - Galia T. Debelouchina
- Department of Chemistry and Biochemistry, University of California San DiegoLa JollaCAUSA
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13
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Abstract
Among structural biology techniques, NMR spectroscopy offers unique capabilities that enable the atomic resolution studies of dynamic and heterogeneous biological systems under physiological and native conditions. Complex biological systems, however, often challenge NMR spectroscopists with their low sensitivity, crowded spectra or large linewidths that reflect their intricate interaction patterns and dynamics. While some of these challenges can be overcome with the development of new spectroscopic approaches, chemical biology can also offer elegant and efficient solutions at the sample preparation stage. In this tutorial, we aim to present several chemical biology tools that enable the preparation of selectively and segmentally labeled protein samples, as well as the introduction of site-specific spectroscopic probes and post-translational modifications. The four tools covered here, namely cysteine chemistry, inteins, native chemical ligation, and unnatural amino acid incorporation, have been developed and optimized in recent years to be more efficient and applicable to a wider range of proteins than ever before. We briefly introduce each tool, describe its advantages and disadvantages in the context of NMR experiments, and offer practical advice for sample preparation and analysis. We hope that this tutorial will introduce beginning researchers in the field to the possibilities chemical biology can offer to NMR spectroscopists, and that it will inspire new and exciting applications in the quest to understand protein function in health and disease.
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Affiliation(s)
- Evan T. Clark
- Department of Chemistry and Biochemistry, Division of Physical Sciences, University of California, San Diego, La Jolla, CA 92093, U.S.A
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, U.S.A
| | - Elanor E. Sievers
- Department of Chemistry and Biochemistry, Division of Physical Sciences, University of California, San Diego, La Jolla, CA 92093, U.S.A
| | - Galia T. Debelouchina
- Department of Chemistry and Biochemistry, Division of Physical Sciences, University of California, San Diego, La Jolla, CA 92093, U.S.A
- Corresponding author: Galia Debelouchina, University of California, San Diego, Natural Sciences Building 4322, 9500 Gilman Dr., La Jolla, CA 92093, 858-534-3038,
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14
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Abstract
Chromatin is a DNA-protein polymer that represents the functional form of the genome. The main building block of chromatin is the nucleosome, a structure that contains 147 base pairs of DNA and two copies each of the histone proteins H2A, H2B, H3 and H4. Previous work has shown that magic angle spinning (MAS) NMR spectroscopy can capture the nucleosome at high resolution although studies have been challenging due to low sensitivity, the presence of dynamic and rigid components, and the complex interaction networks of nucleosomes within the chromatin polymer. Here, we use dynamic nuclear polarization (DNP) to enhance the sensitivity of MAS NMR experiments of nucleosome arrays at 100 K and show that well-resolved 13C-13C MAS NMR correlations can be obtained much more efficiently. We evaluate the effect of temperature on the chemical shifts and linewidths in the spectra and demonstrate that changes are relatively minimal and clustered in regions of histone-DNA or histone-histone contacts. We also compare samples prepared with and without DNA and show that the low temperature 13C-13C correlations exhibit sufficient resolution to detect chemical shift changes and line broadening for residues that form the DNA-histone interface. On the other hand, we show that the measurement of DNP-enhanced 15N-13C histone-histone interactions within the nucleosome core is complicated by the natural 13C abundance network in the sample. Nevertheless, the enhanced sensitivity afforded by DNP can be used to detect long-range correlations between histone residues and DNA. Overall, our experiments demonstrate that DNP-enhanced MAS NMR spectroscopy of chromatin samples yields spectra with high resolution and sensitivity and can be used to capture functionally relevant protein-DNA interactions that have implications for gene regulation and genome organization.
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Affiliation(s)
| | | | - Galia T. Debelouchina
- Corresponding author: Galia Debelouchina, University of California, San Diego, Natural Sciences Building 4322, 9500 Gilman Dr., La Jolla, CA 92093, 858-534-3038,
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15
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Sievers EE, Berkeley RF, Debelouchina GT. Structure determination and optimization of a cysteine-less intein with NMR spectroscopy and molecular dynamics simulations. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.1834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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16
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Ackermann BE, Debelouchina GT. Emerging Contributions of Solid-State NMR Spectroscopy to Chromatin Structural Biology. Front Mol Biosci 2021; 8:741581. [PMID: 34708075 PMCID: PMC8544521 DOI: 10.3389/fmolb.2021.741581] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Accepted: 09/20/2021] [Indexed: 11/13/2022] Open
Abstract
The eukaryotic genome is packaged into chromatin, a polymer of DNA and histone proteins that regulates gene expression and the spatial organization of nuclear content. The repetitive character of chromatin is diversified into rich layers of complexity that encompass DNA sequence, histone variants and post-translational modifications. Subtle molecular changes in these variables can often lead to global chromatin rearrangements that dictate entire gene programs with far reaching implications for development and disease. Decades of structural biology advances have revealed the complex relationship between chromatin structure, dynamics, interactions, and gene expression. Here, we focus on the emerging contributions of magic-angle spinning solid-state nuclear magnetic resonance spectroscopy (MAS NMR), a relative newcomer on the chromatin structural biology stage. Unique among structural biology techniques, MAS NMR is ideally suited to provide atomic level information regarding both the rigid and dynamic components of this complex and heterogenous biological polymer. In this review, we highlight the advantages MAS NMR can offer to chromatin structural biologists, discuss sample preparation strategies for structural analysis, summarize recent MAS NMR studies of chromatin structure and dynamics, and close by discussing how MAS NMR can be combined with state-of-the-art chemical biology tools to reconstitute and dissect complex chromatin environments.
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Affiliation(s)
| | - Galia T. Debelouchina
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, United States
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17
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Elathram N, Ackermann B, Debelouchina GT. Investigating Chromatin Dynamics in Heterochromatin Environments by Solid-State NMR Spectroscopy. Biophys J 2021. [DOI: 10.1016/j.bpj.2020.11.677] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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18
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Abstract
Dynamic nuclear polarization (DNP) has shown great promise as a tool to enhance the nuclear magnetic resonance signals of proteins in the cellular environment. As sensitivity increases, the ability to select and efficiently polarize a specific macromolecule over the cellular background has become desirable. Herein, we address this need and present a tetrazine-based DNP agent that can be targeted selectively to proteins containing the unnatural amino acid (UAA) norbornene-lysine. This UAA can be introduced efficiently into the cellular milieu by genetic means. Our approach is bio-orthogonal and easily adaptable to any protein of interest. We illustrate the scope of our methodology and investigate the DNP transfer mechanisms in several biological systems. Our results shed light on the complex polarization-transfer pathways in targeted DNP and ultimately pave the way to selective DNP-enhanced NMR spectroscopy in both bacterial and mammalian cells.
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Affiliation(s)
- Byung Joon Lim
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
| | - Bryce E. Ackermann
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
| | - Galia T. Debelouchina
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA
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19
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Elathram N, Debelouchina GT. The Effect of Histone H4 K20 Methylation on Chromatin Compaction. Biophys J 2020. [DOI: 10.1016/j.bpj.2019.11.2163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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20
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Beh LY, Debelouchina GT, Clay DM, Thompson RE, Lindblad KA, Hutton ER, Bracht JR, Sebra RP, Muir TW, Landweber LF. Identification of a DNA N6-Adenine Methyltransferase Complex and Its Impact on Chromatin Organization. Cell 2019; 177:1781-1796.e25. [PMID: 31104845 DOI: 10.1016/j.cell.2019.04.028] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 01/31/2019] [Accepted: 04/12/2019] [Indexed: 11/27/2022]
Abstract
DNA N6-adenine methylation (6mA) has recently been described in diverse eukaryotes, spanning unicellular organisms to metazoa. Here, we report a DNA 6mA methyltransferase complex in ciliates, termed MTA1c. It consists of two MT-A70 proteins and two homeobox-like DNA-binding proteins and specifically methylates dsDNA. Disruption of the catalytic subunit, MTA1, in the ciliate Oxytricha leads to genome-wide loss of 6mA and abolishment of the consensus ApT dimethylated motif. Mutants fail to complete the sexual cycle, which normally coincides with peak MTA1 expression. We investigate the impact of 6mA on nucleosome occupancy in vitro by reconstructing complete, full-length Oxytricha chromosomes harboring 6mA in native or ectopic positions. We show that 6mA directly disfavors nucleosomes in vitro in a local, quantitative manner, independent of DNA sequence. Furthermore, the chromatin remodeler ACF can overcome this effect. Our study identifies a diverged DNA N6-adenine methyltransferase and defines the role of 6mA in chromatin organization.
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Affiliation(s)
- Leslie Y Beh
- Departments of Biochemistry & Molecular Biophysics and Biological Sciences, Columbia University, New York, NY 10032, USA; Department of Chemistry, Princeton University, Princeton, NJ 08544, USA; Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
| | | | - Derek M Clay
- Departments of Biochemistry & Molecular Biophysics and Biological Sciences, Columbia University, New York, NY 10032, USA
| | - Robert E Thompson
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - Kelsi A Lindblad
- Departments of Biochemistry & Molecular Biophysics and Biological Sciences, Columbia University, New York, NY 10032, USA
| | - Elizabeth R Hutton
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
| | - John R Bracht
- Department of Biology, American University, Washington, DC 20016, USA
| | - Robert P Sebra
- Icahn Institute and Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Tom W Muir
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA.
| | - Laura F Landweber
- Departments of Biochemistry & Molecular Biophysics and Biological Sciences, Columbia University, New York, NY 10032, USA.
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21
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Affiliation(s)
- Bryce E. Ackermann
- Department of Chemistry and BiochemistryUniversity of California, San Diego 9500 Gilman Dr. La Jolla CA 92093 USA
| | - Galia T. Debelouchina
- Department of Chemistry and BiochemistryUniversity of California, San Diego 9500 Gilman Dr. La Jolla CA 92093 USA
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22
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Ackermann BE, Debelouchina GT. Heterochromatin Protein HP1α Gelation Dynamics Revealed by Solid-State NMR Spectroscopy. Angew Chem Int Ed Engl 2019; 58:6300-6305. [PMID: 30845353 DOI: 10.1002/anie.201901141] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 03/07/2019] [Indexed: 11/12/2022]
Abstract
Heterochromatin protein 1α (HP1α) undergoes liquid-liquid phase separation (LLPS) and forms liquid droplets and gels in vitro, properties that also appear to be central to its biological function in heterochromatin compaction and regulation. Here we use solid-state NMR spectroscopy to track the conformational dynamics of phosphorylated HP1α during its transformation from the liquid to the gel state. Using experiments designed to probe distinct dynamic modes, we identify regions with varying mobilities within HP1α molecules and show that specific serine residues uniquely contribute to gel formation. The addition of chromatin disturbs the gelation process while preserving the conformational dynamics within individual bulk HP1α molecules. Our study provides a glimpse into the dynamic architecture of dense HP1α phases and showcases the potential of solid-state NMR to detect an elusive biophysical regime of phase separating biomolecules.
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Affiliation(s)
- Bryce E Ackermann
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA, 92093, USA
| | - Galia T Debelouchina
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA, 92093, USA
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23
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Ackermann BE, Debelouchina GT. Characterizing HP1-Driven Chromatin Compaction using Nuclear Magnetic Resonance Spectroscopy. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.2616] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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24
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Debelouchina GT. The Role of Ubiquitin in Chromatin Structural Organization. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.2152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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25
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Johnson JG, Wang B, Debelouchina GT, Novick RP, Muir TW. Increasing AIP Macrocycle Size Reveals Key Features of agr Activation in Staphylococcus aureus. Chembiochem 2015; 16:1093-100. [PMID: 25801678 DOI: 10.1002/cbic.201500006] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2015] [Indexed: 11/09/2022]
Abstract
The agr locus in the commensal human pathogen, Staphylococcus aureus, is a two-promoter regulon with allelic variability that produces a quorum-sensing circuit involved in regulating virulence within the bacterium. Secretion of unique autoinducing peptides (AIPs) and detection of their concentrations by AgrC, a transmembrane receptor histidine kinase, coordinates local bacterial population density with global changes in gene expression. The finding that staphylococcal virulence can be inhibited through antagonism of this quorum-sensing pathway has fueled tremendous interest in understanding the structure-activity relationships underlying the AIP-AgrC interaction. The defining structural feature of the AIP is a 16-membered, thiolactone-containing macrocycle. Surprisingly, the importance of ring size on agr activation or inhibition has not been explored. In this study, we address this deficiency through the synthesis and functional analysis of AIP analogues featuring enlarged and reduced macrocycles. Notably, this study is the first to interrogate AIP function by using both established cell-based reporter gene assays and newly developed in vitro AgrC-I binding and autophosphorylation activity assays. Based on our data, we present a model for robust agr activation involving a cooperative, three-points-of-contact interaction between the AIP macrocycle and AgrC.
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Affiliation(s)
- Jeffrey G Johnson
- Department of Chemistry, Princeton University, Frick Chemistry Building, Washington Road, Princeton, NJ 08544 (USA); Graduate Program, The Rockefeller University, 1230 York Avenue, New York, NY 10065 (USA); Tri-Institutional Training Program in Chemical Biology, Weil-Cornell/Memorial Sloan Kettering/Rockefeller University, New York, NY 10065 (USA)
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26
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Su Y, Sarell CJ, Eddy MT, Debelouchina GT, Andreas LB, Pashley CL, Radford SE, Griffin RG. Secondary structure in the core of amyloid fibrils formed from human β₂m and its truncated variant ΔN6. J Am Chem Soc 2014; 136:6313-25. [PMID: 24679070 PMCID: PMC4017606 DOI: 10.1021/ja4126092] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
![]()
Amyloid
fibrils formed from initially soluble proteins with diverse
sequences are associated with an array of human diseases. In the human
disorder, dialysis-related amyloidosis (DRA), fibrils contain two
major constituents, full-length human β2-microglobulin
(hβ2m) and a truncation variant, ΔN6 which
lacks the N-terminal six amino acids. These fibrils are assembled
from initially natively folded proteins with an all antiparallel β-stranded
structure. Here, backbone conformations of wild-type hβ2m and ΔN6 in their amyloid forms have been determined
using a combination of dilute isotopic labeling strategies and multidimensional
magic angle spinning (MAS) NMR techniques at high magnetic fields,
providing valuable structural information at the atomic-level about
the fibril architecture. The secondary structures of both fibril types,
determined by the assignment of ∼80% of the backbone resonances
of these 100- and 94-residue proteins, respectively, reveal substantial
backbone rearrangement compared with the location of β-strands
in their native immunoglobulin folds. The identification of seven
β-strands in hβ2m fibrils indicates that approximately
70 residues are in a β-strand conformation in the fibril core.
By contrast, nine β-strands comprise the fibrils formed from
ΔN6, indicating a more extensive core. The precise location
and length of β-strands in the two fibril forms also differ.
The results indicate fibrils of ΔN6 and hβ2m have an extensive core architecture involving the majority of residues
in the polypeptide sequence. The common elements of the backbone structure
of the two proteins likely facilitates their ability to copolymerize
during amyloid fibril assembly.
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Affiliation(s)
- Yongchao Su
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology Cambridge, Massachusetts 02139, United States
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27
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Frederick KK, Debelouchina GT, Kayatekin C, Dorminy T, Jacavone AC, Griffin RG, Lindquist S. Distinct prion strains are defined by amyloid core structure and chaperone binding site dynamics. ACTA ACUST UNITED AC 2014; 21:295-305. [PMID: 24485763 DOI: 10.1016/j.chembiol.2013.12.013] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Revised: 11/14/2013] [Accepted: 12/12/2013] [Indexed: 10/25/2022]
Abstract
Yeast prions are self-templating protein-based mechanisms of inheritance whose conformational changes lead to the acquisition of diverse new phenotypes. The best studied of these is the prion domain (NM) of Sup35, which forms an amyloid that can adopt several distinct conformations (strains) that produce distinct phenotypes. Using magic-angle spinning nuclear magnetic resonance spectroscopy, we provide a detailed look at the dynamic properties of these forms over a broad range of timescales. We establish that different prion strains have distinct amyloid structures, with many side chains in different chemical environments. Surprisingly, the prion strain with a larger fraction of rigid residues also has a larger fraction of highly mobile residues. Differences in mobility correlate with differences in interaction with the prion-partitioning factor Hsp104 in vivo, perhaps explaining strain-specific differences in inheritance.
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Affiliation(s)
- Kendra K Frederick
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Galia T Debelouchina
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Francis Bitter Magnet Labaratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Can Kayatekin
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Tea Dorminy
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Angela C Jacavone
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Francis Bitter Magnet Labaratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Robert G Griffin
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Francis Bitter Magnet Labaratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Susan Lindquist
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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28
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Debelouchina GT, Bayro MJ, Fitzpatrick AW, Ladizhansky V, Colvin MT, Caporini MA, Jaroniec CP, Bajaj VS, Rosay M, Macphee CE, Vendruscolo M, Maas WE, Dobson CM, Griffin RG. Higher order amyloid fibril structure by MAS NMR and DNP spectroscopy. J Am Chem Soc 2013; 135:19237-47. [PMID: 24304221 DOI: 10.1021/ja409050a] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Protein magic angle spinning (MAS) NMR spectroscopy has generated structural models of several amyloid fibril systems, thus providing valuable information regarding the forces and interactions that confer the extraordinary stability of the amyloid architecture. Despite these advances, however, obtaining atomic resolution information describing the higher levels of structural organization within the fibrils remains a significant challenge. Here, we detail MAS NMR experiments and sample labeling schemes designed specifically to probe such higher order amyloid structure, and we have applied them to the fibrils formed by an eleven-residue segment of the amyloidogenic protein transthyretin (TTR(105-115)). These experiments have allowed us to define unambiguously not only the arrangement of the peptide β-strands into β-sheets but also the β-sheet interfaces within each protofilament, and in addition to identify the nature of the protofilament-to-protofilament contacts that lead to the formation of the complete fibril. Our efforts have resulted in 111 quantitative distance and torsion angle restraints (10 per residue) that describe the various levels of structure organization. The experiments benefited extensively from the use of dynamic nuclear polarization (DNP), which in some cases allowed us to shorten the data acquisition time from days to hours and to improve significantly the signal-to-noise ratios of the spectra. The β-sheet interface and protofilament interactions identified here revealed local variations in the structure that result in multiple peaks for the exposed N- and C-termini of the peptide and in inhomogeneous line-broadening for the residues buried within the interior of the fibrils.
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Affiliation(s)
- Galia T Debelouchina
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
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29
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Fitzpatrick AWP, Debelouchina GT, Bayro MJ, Clare DK, Caporini MA, Bajaj VS, Jaroniec CP, Wang L, Ladizhansky V, Müller SA, MacPhee CE, Waudby CA, Mott HR, De Simone A, Knowles TPJ, Saibil HR, Vendruscolo M, Orlova EV, Griffin RG, Dobson CM. Atomic structure and hierarchical assembly of a cross-β amyloid fibril. Proc Natl Acad Sci U S A 2013; 110:5468-73. [PMID: 23513222 PMCID: PMC3619355 DOI: 10.1073/pnas.1219476110] [Citation(s) in RCA: 395] [Impact Index Per Article: 35.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The cross-β amyloid form of peptides and proteins represents an archetypal and widely accessible structure consisting of ordered arrays of β-sheet filaments. These complex aggregates have remarkable chemical and physical properties, and the conversion of normally soluble functional forms of proteins into amyloid structures is linked to many debilitating human diseases, including several common forms of age-related dementia. Despite their importance, however, cross-β amyloid fibrils have proved to be recalcitrant to detailed structural analysis. By combining structural constraints from a series of experimental techniques spanning five orders of magnitude in length scale--including magic angle spinning nuclear magnetic resonance spectroscopy, X-ray fiber diffraction, cryoelectron microscopy, scanning transmission electron microscopy, and atomic force microscopy--we report the atomic-resolution (0.5 Å) structures of three amyloid polymorphs formed by an 11-residue peptide. These structures reveal the details of the packing interactions by which the constituent β-strands are assembled hierarchically into protofilaments, filaments, and mature fibrils.
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Affiliation(s)
- Anthony W. P. Fitzpatrick
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - Galia T. Debelouchina
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Marvin J. Bayro
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Daniel K. Clare
- Institute of Structural and Molecular Biology, Birkbeck College, London WC1E 7HX, United Kingdom
| | - Marc A. Caporini
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Vikram S. Bajaj
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Christopher P. Jaroniec
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Luchun Wang
- Institute of Structural and Molecular Biology, Birkbeck College, London WC1E 7HX, United Kingdom
| | - Vladimir Ladizhansky
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | | | - Cait E. MacPhee
- School of Physics, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
| | - Christopher A. Waudby
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
- Institute of Structural and Molecular Biology, Birkbeck College, London WC1E 7HX, United Kingdom
| | - Helen R. Mott
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, United Kingdom; and
| | - Alfonso De Simone
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
- Division of Molecular Biosciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Tuomas P. J. Knowles
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
| | - Helen R. Saibil
- Institute of Structural and Molecular Biology, Birkbeck College, London WC1E 7HX, United Kingdom
| | - Michele Vendruscolo
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
| | - Elena V. Orlova
- Institute of Structural and Molecular Biology, Birkbeck College, London WC1E 7HX, United Kingdom
| | - Robert G. Griffin
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
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30
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Sarell CJ, Woods LA, Su Y, Debelouchina GT, Ashcroft AE, Griffin RG, Stockley PG, Radford SE. Expanding the repertoire of amyloid polymorphs by co-polymerization of related protein precursors. J Biol Chem 2013; 288:7327-37. [PMID: 23329840 PMCID: PMC3591641 DOI: 10.1074/jbc.m112.447524] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Amyloid fibrils can be generated from proteins with diverse sequences and folds. Although amyloid fibrils assembled in vitro commonly involve a single protein precursor, fibrils formed in vivo can contain more than one protein sequence. How fibril structure and stability differ in fibrils composed of single proteins (homopolymeric fibrils) from those generated by co-polymerization of more than one protein sequence (heteropolymeric fibrils) is poorly understood. Here we compare the structure and stability of homo and heteropolymeric fibrils formed from human β2-microglobulin and its truncated variant ΔN6. We use an array of approaches (limited proteolysis, magic angle spinning NMR, Fourier transform infrared spectroscopy, and fluorescence) combined with measurements of thermodynamic stability to characterize the different fibril types. The results reveal fibrils with different structural properties, different side-chain packing, and strikingly different stabilities. These findings demonstrate how co-polymerization of related precursor sequences can expand the repertoire of structural and thermodynamic polymorphism in amyloid fibrils to an extent that is greater than that obtained by polymerization of a single precursor alone.
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Affiliation(s)
- Claire J Sarell
- Astbury Centre for Structural Molecular Biology and School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
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31
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Bayro MJ, Debelouchina GT, Eddy MT, Birkett NR, MacPhee CE, Rosay M, Maas WE, Dobson CM, Griffin RG. Intermolecular structure determination of amyloid fibrils with magic-angle spinning and dynamic nuclear polarization NMR. J Am Chem Soc 2011; 133:13967-74. [PMID: 21774549 DOI: 10.1021/ja203756x] [Citation(s) in RCA: 148] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We describe magic-angle spinning NMR experiments designed to elucidate the interstrand architecture of amyloid fibrils. Three methods are introduced for this purpose, two being based on the analysis of long-range (13)C-(13)C correlation spectra and the third based on the identification of intermolecular interactions in (13)C-(15)N spectra. We show, in studies of fibrils formed by the 86-residue SH3 domain of PI3 kinase (PI3-SH3 or PI3K-SH3), that efficient (13)C-(13)C correlation spectra display a resonance degeneracy that establishes a parallel, in-register alignment of the proteins in the amyloid fibrils. In addition, this degeneracy can be circumvented to yield direct intermolecular constraints. The (13)C-(13)C experiments are corroborated by (15)N-(13)C correlation spectra obtained from a mixed [(15)N,(12)C]/[(14)N,(13)C] sample which directly quantify interstrand distances. Furthermore, when the spectra are recorded with signal enhancement provided by dynamic nuclear polarization (DNP) at 100 K, we demonstrate a dramatic increase (from 23 to 52) in the number of intermolecular (15)N-(13)C constraints detectable in the spectra. The increase in the information content is due to the enhanced signal intensities and to the fact that dynamic processes, leading to spectral intensity losses, are quenched at low temperatures. Thus, acquisition of low temperature spectra addresses a problem that is frequently encountered in MAS spectra of proteins. In total, the experiments provide 111 intermolecular (13)C-(13)C and (15)N-(13)C constraints that establish that the PI3-SH3 protein strands are aligned in a parallel, in-register arrangement within the amyloid fibril.
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Affiliation(s)
- Marvin J Bayro
- Francis Bitter Magnet Laboratory, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, 02139, United States
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32
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Abstract
Microwave driven dynamic nuclear polarization (DNP) is a process in which the large polarization present in an electron spin reservoir is transferred to nuclei, thereby enhancing NMR signal intensities. In solid dielectrics there are three mechanisms that mediate this transfer--the solid effect (SE), the cross effect (CE), and thermal mixing (TM). Historically these mechanisms have been discussed theoretically using thermodynamic parameters and average spin interactions. However, the SE and the CE can also be modeled quantum mechanically with a system consisting of a small number of spins and the results provide a foundation for the calculations involving TM. In the case of the SE, a single electron-nuclear spin pair is sufficient to explain the polarization mechanism, while the CE requires participation of two electrons and a nuclear spin, and can be used to understand the improved DNP enhancements observed using biradical polarizing agents. Calculations establish the relations among the electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) frequencies and the microwave irradiation frequency that must be satisfied for polarization transfer via the SE or the CE. In particular, if δ, Δ < ω(0I), where δ and Δ are the homogeneous linewidth and inhomogeneous breadth of the EPR spectrum, respectively, we verify that the SE occurs when ω(M) = ω(0S) ± ω(0I), where ω(M), ω(0S) and ω(0I) are, respectively, the microwave, and the EPR and NMR frequencies. Alternatively, when Δ > ω(0I) > δ, the CE dominates the polarization transfer. This two-electron process is optimized when ω(0S(1))-ω(0S(2)) = ω(0I) and ω(M)~ω(0S(1)) or ω(0S(2)), where ω(0S(1)) and ω(0S(2)) are the EPR Larmor frequencies of the two electrons. Using these matching conditions, we calculate the evolution of the density operator from electron Zeeman order to nuclear Zeeman order for both the SE and the CE. The results provide insights into the influence of the microwave irradiation field, the external magnetic field, and the electron-electron and electron-nuclear interactions on DNP enhancements.
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Affiliation(s)
- Kan-Nian Hu
- Francis Bitter Magnet Laboratory, and Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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Debelouchina GT, Platt GW, Bayro MJ, Radford SE, Griffin RG. Intermolecular alignment in β2-microglobulin amyloid fibrils. J Am Chem Soc 2010. [PMID: 21077676 DOI: 10.1021/ja1079871] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/19/2023]
Abstract
The deposition of amyloid-like fibrils, composed primarily of the 99-residue protein β2-microglobulin (β2m), is one of the characteristic symptoms of dialysis-related amyloidosis. Fibrils formed in vitro at low pH and low salt concentration share many properties with the disease related fibrils and have been extensively studied by a number of biochemical and biophysical methods. These fibrils contain a significant β-sheet core and have a complex cryoEM electron density profile. Here, we investigate the intrasheet arrangement of the fibrils by means of (15)N-(13)C MAS NMR correlation spectroscopy. We utilize a fibril sample grown from a 50:50 mixture of (15)N,(12)C- and (14)N,(13)C-labeled β2m monomers, the latter prepared using 2-(13)C glycerol as the carbon source. Together with the use of ZF-TEDOR mixing, this sample allowed us to observe intermolecular (15)N-(13)C backbone-to-backbone contacts with excellent resolution and good sensitivity. The results are consistent with a parallel, in-register arrangement of the protein subunits in the fibrils and suggest that a significant structural reorganization occurs from the native to the fibril state.
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Affiliation(s)
- Galia T Debelouchina
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Abstract
The deposition of amyloid-like fibrils, composed primarily of the 99-residue protein β2-microglobulin (β2m), is one of the characteristic symptoms of dialysis-related amyloidosis. Fibrils formed in vitro at low pH and low salt concentration share many properties with the disease related fibrils and have been extensively studied by a number of biochemical and biophysical methods. These fibrils contain a significant β-sheet core and have a complex cryoEM electron density profile. Here, we investigate the intrasheet arrangement of the fibrils by means of (15)N-(13)C MAS NMR correlation spectroscopy. We utilize a fibril sample grown from a 50:50 mixture of (15)N,(12)C- and (14)N,(13)C-labeled β2m monomers, the latter prepared using 2-(13)C glycerol as the carbon source. Together with the use of ZF-TEDOR mixing, this sample allowed us to observe intermolecular (15)N-(13)C backbone-to-backbone contacts with excellent resolution and good sensitivity. The results are consistent with a parallel, in-register arrangement of the protein subunits in the fibrils and suggest that a significant structural reorganization occurs from the native to the fibril state.
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Affiliation(s)
- Galia T Debelouchina
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Flook MM, Gerber LCH, Debelouchina GT, Schrock RR. Z-Selective and Syndioselective Ring-Opening Metathesis Polymerization (ROMP) Initiated by MonoAryloxidePyrrolide (MAP) Catalysts. Macromolecules 2010; 43:7515-7522. [PMID: 21499508 DOI: 10.1021/ma101375v] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report the Z-selective and syndioselective polymerization of 2,3-bis(trifluoromethyl)bicyclo[2.2.1]hepta-2,5-diene (NBDF6) and 3-methyl-3-phenylcyclopropene (MPCP) by monoaryloxide monopyrrolide imido alkylidene (MAP) catalysts of Mo. The mechanism of polymerization with syn-Mo(NAd)(CHCMe(2)Ph)(Pyr)(OHIPT) (1; Ad = 1-adamantyl, OHIPT = O-2,6-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3)) as the initiator is proposed to consist of addition of monomer to the syn initiator to yield a syn first insertion product and propagation via syn insertion products. In contrast, the mechanism of polymerization with syn-Mo(NAr)(CHCMe(2)Ph)(Pyr)(OTPP) (4; Ar = 2,6-i-Pr(2)C(6)H(3), OTPP = 2,3,5,6-Ph(4)C(6)H) as the initiator at -78 °C consists of addition of monomer to the syn initiator to yield an anti first insertion product and propagation via anti insertion products. Polymerizations of NBDF6 and MPCP at room temperature initiated by 4 led to polymers without a regular structure. We propose that the syndiotacticity of cis polymers is the consequence of the required inversion at the metal center with each insertion of monomer, i.e., stereogenic metal control of the polymer structure. We also propose that the two mechanisms for forming cis,syndiotactic polymers arise as a consequence of the relative steric bulk of the imido and phenoxide ligands.
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Affiliation(s)
- Margaret M Flook
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
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Debelouchina GT, Platt GW, Bayro MJ, Radford SE, Griffin RG. Magic angle spinning NMR analysis of beta2-microglobulin amyloid fibrils in two distinct morphologies. J Am Chem Soc 2010; 132:10414-23. [PMID: 20662519 PMCID: PMC2919207 DOI: 10.1021/ja102775u] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Beta(2)-microglobulin (beta(2)m) is the major structural component of amyloid fibrils deposited in a condition known as dialysis-related amyloidosis. Despite numerous studies that have elucidated important aspects of the fibril formation process in vitro, and a magic angle spinning (MAS) NMR study of the fibrils formed by a small peptide fragment, structural details of beta(2)m fibrils formed by the full-length 99-residue protein are largely unknown. Here, we present a site-specific MAS NMR analysis of fibrils formed by the full-length beta(2)m protein and compare spectra of fibrils prepared under two different conditions. Specifically, long straight (LS) fibrils are formed at pH 2.5, while a very different morphology denoted as worm-like (WL) fibrils is observed in preparations at pH 3.6. High-resolution MAS NMR spectra have allowed us to obtain (13)C and (15)N resonance assignments for 64 residues of beta(2)m in LS fibrils, including part of the highly mobile N-terminus. Approximately 25 residues did not yield observable signals. Chemical shift analysis of the sequentially assigned residues indicates that these fibrils contain an extensive beta-sheet core organized in a non-native manner, with a trans-P32 conformation. In contrast, WL fibrils exhibit more extensive dynamics and appear to have a smaller beta-sheet core than LS fibrils, although both cores seem to share some common elements. Our results suggest that the distinct macroscopic morphological features observed for the two types of fibrils result from variations in structure and dynamics at the molecular level.
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Affiliation(s)
- Galia T. Debelouchina
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Geoffrey W. Platt
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
- Institute of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Marvin J. Bayro
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Sheena E. Radford
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
- Institute of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Robert G. Griffin
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Debelouchina GT, Bayro MJ, van der Wel PCA, Caporini MA, Barnes AB, Rosay M, Maas WE, Griffin RG. Dynamic nuclear polarization-enhanced solid-state NMR spectroscopy of GNNQQNY nanocrystals and amyloid fibrils. Phys Chem Chem Phys 2010; 12:5911-9. [PMID: 20454733 DOI: 10.1039/c003661g] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Dynamic nuclear polarization (DNP) utilizes the inherently larger polarization of electrons to enhance the sensitivity of conventional solid-state NMR experiments at low temperature. Recent advances in instrumentation development and sample preparation have transformed this field and have opened up new opportunities for its application to biological systems. Here, we present DNP-enhanced (13)C-(13)C and (15)N-(13)C correlation experiments on GNNQQNY nanocrystals and amyloid fibrils acquired at 9.4 T and 100 K and demonstrate that DNP can be used to obtain assignments and site-specific structural information very efficiently. We investigate the influence of temperature on the resolution, molecular conformation, structural integrity and dynamics in these two systems. In addition, we assess the low-temperature performance of two commonly used solid-state NMR experiments, proton-driven spin diffusion (PDSD) and transferred echo double resonance (TEDOR), and discuss their potential as tools for measurement of structurally relevant distances at low temperature in combination with DNP.
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Affiliation(s)
- Galia T Debelouchina
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Abstract
The synthesis and characterization of a biradical containing a 1,3-bisdiphenylene-2-phenylallyl (BDPA) free radical covalently attached to a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) free radical are described. The synthesis of the biradical is a step toward improved polarizing agents for dynamic nuclear polarization (DNP).
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Affiliation(s)
- Eric L Dane
- Massachusetts Institute of Technology and Francis Bitter Magnet Laboratory, Cambridge, Massachusetts 02139, USA
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Debelouchina GT, Bayro MJ, Platt GW, Radford SE, Griffin RG. Solid-state NMR Investigation of b2-Microglobulin Fibril Structure and Dynamics. Biophys J 2009. [DOI: 10.1016/j.bpj.2008.12.353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
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Maly T, Debelouchina GT, Bajaj VS, Hu KN, Joo CG, Mak–Jurkauskas ML, Sirigiri JR, van der Wel PCA, Herzfeld J, Temkin RJ, Griffin RG. Dynamic nuclear polarization at high magnetic fields. J Chem Phys 2008; 128:052211. [PMID: 18266416 PMCID: PMC2770872 DOI: 10.1063/1.2833582] [Citation(s) in RCA: 534] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Dynamic nuclear polarization (DNP) is a method that permits NMR signal intensities of solids and liquids to be enhanced significantly, and is therefore potentially an important tool in structural and mechanistic studies of biologically relevant molecules. During a DNP experiment, the large polarization of an exogeneous or endogeneous unpaired electron is transferred to the nuclei of interest (I) by microwave (microw) irradiation of the sample. The maximum theoretical enhancement achievable is given by the gyromagnetic ratios (gamma(e)gamma(l)), being approximately 660 for protons. In the early 1950s, the DNP phenomenon was demonstrated experimentally, and intensively investigated in the following four decades, primarily at low magnetic fields. This review focuses on recent developments in the field of DNP with a special emphasis on work done at high magnetic fields (> or =5 T), the regime where contemporary NMR experiments are performed. After a brief historical survey, we present a review of the classical continuous wave (cw) DNP mechanisms-the Overhauser effect, the solid effect, the cross effect, and thermal mixing. A special section is devoted to the theory of coherent polarization transfer mechanisms, since they are potentially more efficient at high fields than classical polarization schemes. The implementation of DNP at high magnetic fields has required the development and improvement of new and existing instrumentation. Therefore, we also review some recent developments in microw and probe technology, followed by an overview of DNP applications in biological solids and liquids. Finally, we outline some possible areas for future developments.
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Affiliation(s)
- Thorsten Maly
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Galia T. Debelouchina
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Vikram S. Bajaj
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Kan-Nian Hu
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Chan-Gyu Joo
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | | | - Jagadishwar R. Sirigiri
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Patrick C. A. van der Wel
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Judith Herzfeld
- Department of Chemistry, Brandels University, Waltham, Massachusetts 02454, USA
| | - Richard J. Temkin
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Robert G. Griffin
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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