1
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Heo L, Feig M. One bead per residue can describe all-atom protein structures. Structure 2024; 32:97-111.e6. [PMID: 38000367 PMCID: PMC10872525 DOI: 10.1016/j.str.2023.10.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 09/16/2023] [Accepted: 10/30/2023] [Indexed: 11/26/2023]
Abstract
Atomistic resolution is the standard for high-resolution biomolecular structures, but experimental structural data are often at lower resolution. Coarse-grained models are also used extensively in computational studies to reach biologically relevant spatial and temporal scales. This study explores the use of advanced machine learning networks for reconstructing atomistic models from reduced representations. The main finding is that a single bead per amino acid residue allows construction of accurate and stereochemically realistic all-atom structures with minimal loss of information. This suggests that lower resolution representations of proteins may be sufficient for many applications when combined with a machine learning framework that encodes knowledge from known structures. Practical applications include the rapid addition of atomistic detail to low-resolution structures from experiment or computational coarse-grained models. The application of rapid, deterministic all-atom reconstruction within multi-scale frameworks is further demonstrated with a rapid protocol for the generation of accurate models from cryo-EM densities close to experimental structures.
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Affiliation(s)
- Lim Heo
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
| | - Michael Feig
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
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2
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Zielinski M, Peralta Reyes FS, Gremer L, Schemmert S, Frieg B, Schäfer LU, Willuweit A, Donner L, Elvers M, Nilsson LNG, Syvänen S, Sehlin D, Ingelsson M, Willbold D, Schröder GF. Cryo-EM of Aβ fibrils from mouse models find tg-APP ArcSwe fibrils resemble those found in patients with sporadic Alzheimer's disease. Nat Neurosci 2023; 26:2073-2080. [PMID: 37973869 PMCID: PMC10689242 DOI: 10.1038/s41593-023-01484-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2023] [Accepted: 10/06/2023] [Indexed: 11/19/2023]
Abstract
The use of transgenic mice displaying amyloid-β (Aβ) brain pathology has been essential for the preclinical assessment of new treatment strategies for Alzheimer's disease. However, the properties of Aβ in such mice have not been systematically compared to Aβ in the brains of patients with Alzheimer's disease. Here, we determined the structures of nine ex vivo Aβ fibrils from six different mouse models by cryogenic-electron microscopy. We found novel Aβ fibril structures in the APP/PS1, ARTE10 and tg-SwDI models, whereas the human type II filament fold was found in the ARTE10, tg-APPSwe and APP23 models. The tg-APPArcSwe mice showed an Aβ fibril whose structure resembles the human type I filament found in patients with sporadic Alzheimer's disease. A detailed assessment of the Aβ fibril structure is key to the selection of adequate mouse models for the preclinical development of novel plaque-targeting therapeutics and positron emission tomography imaging tracers in Alzheimer's disease.
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Affiliation(s)
- Mara Zielinski
- Institute of Biological Information Processing, Structural Biochemistry (IBI-7), Forschungszentrum Jülich, Jülich, Germany
- JuStruct, Jülich Center for Structural Biology, Forschungszentrum Jülich, Jülich, Germany
| | | | - Lothar Gremer
- Institute of Biological Information Processing, Structural Biochemistry (IBI-7), Forschungszentrum Jülich, Jülich, Germany.
- JuStruct, Jülich Center for Structural Biology, Forschungszentrum Jülich, Jülich, Germany.
- Institut für Physikalische Biologie, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
| | - Sarah Schemmert
- Institute of Biological Information Processing, Structural Biochemistry (IBI-7), Forschungszentrum Jülich, Jülich, Germany
| | - Benedikt Frieg
- Institute of Biological Information Processing, Structural Biochemistry (IBI-7), Forschungszentrum Jülich, Jülich, Germany
- JuStruct, Jülich Center for Structural Biology, Forschungszentrum Jülich, Jülich, Germany
| | - Luisa U Schäfer
- Institute of Biological Information Processing, Structural Biochemistry (IBI-7), Forschungszentrum Jülich, Jülich, Germany
- JuStruct, Jülich Center for Structural Biology, Forschungszentrum Jülich, Jülich, Germany
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Antje Willuweit
- Institute of Neuroscience and Medicine, Medical Imaging Physics (INM-4), Forschungszentrum Jülich, Jülich, Germany
| | - Lili Donner
- Department of Vascular and Endovascular Surgery, University Hospital Düsseldorf, Heinrich Heine University, Düsseldorf, Germany
| | - Margitta Elvers
- Department of Vascular and Endovascular Surgery, University Hospital Düsseldorf, Heinrich Heine University, Düsseldorf, Germany
| | - Lars N G Nilsson
- Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway
| | - Stina Syvänen
- Department of Public Health and Caring Sciences, Molecular Geriatrics, Rudbeck Laboratory, Uppsala University, Uppsala, Sweden
| | - Dag Sehlin
- Department of Public Health and Caring Sciences, Molecular Geriatrics, Rudbeck Laboratory, Uppsala University, Uppsala, Sweden
| | - Martin Ingelsson
- Department of Public Health and Caring Sciences, Molecular Geriatrics, Rudbeck Laboratory, Uppsala University, Uppsala, Sweden
- Krembil Brain Institute, University Health Network, Toronto, Ontario, Canada
- Tanz Centre for Research in Neurodegenerative Diseases, Departments of Medicine and Laboratory Medicine & Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Dieter Willbold
- Institute of Biological Information Processing, Structural Biochemistry (IBI-7), Forschungszentrum Jülich, Jülich, Germany.
- JuStruct, Jülich Center for Structural Biology, Forschungszentrum Jülich, Jülich, Germany.
- Institut für Physikalische Biologie, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
| | - Gunnar F Schröder
- Institute of Biological Information Processing, Structural Biochemistry (IBI-7), Forschungszentrum Jülich, Jülich, Germany.
- JuStruct, Jülich Center for Structural Biology, Forschungszentrum Jülich, Jülich, Germany.
- Physics Department, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
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3
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Yvonnesdotter L, Rovšnik U, Blau C, Lycksell M, Howard RJ, Lindahl E. Automated simulation-based membrane protein refinement into cryo-EM data. Biophys J 2023; 122:2773-2781. [PMID: 37277992 PMCID: PMC10397807 DOI: 10.1016/j.bpj.2023.05.033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 04/02/2023] [Accepted: 05/31/2023] [Indexed: 06/07/2023] Open
Abstract
The resolution revolution has increasingly enabled single-particle cryogenic electron microscopy (cryo-EM) reconstructions of previously inaccessible systems, including membrane proteins-a category that constitutes a disproportionate share of drug targets. We present a protocol for using density-guided molecular dynamics simulations to automatically refine atomistic models into membrane protein cryo-EM maps. Using adaptive force density-guided simulations as implemented in the GROMACS molecular dynamics package, we show how automated model refinement of a membrane protein is achieved without the need to manually tune the fitting force ad hoc. We also present selection criteria to choose the best-fit model that balances stereochemistry and goodness of fit. The proposed protocol was used to refine models into a new cryo-EM density of the membrane protein maltoporin, either in a lipid bilayer or detergent micelle, and we found that results do not substantially differ from fitting in solution. Fitted structures satisfied classical model-quality metrics and improved the quality and the model-to-map correlation of the x-ray starting structure. Additionally, the density-guided fitting in combination with generalized orientation-dependent all-atom potential was used to correct the pixel-size estimation of the experimental cryo-EM density map. This work demonstrates the applicability of a straightforward automated approach to fitting membrane protein cryo-EM densities. Such computational approaches promise to facilitate rapid refinement of proteins under different conditions or with various ligands present, including targets in the highly relevant superfamily of membrane proteins.
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Affiliation(s)
- Linnea Yvonnesdotter
- Science for Life Laboratory & Swedish e-Science Research Center, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden
| | - Urška Rovšnik
- Science for Life Laboratory & Swedish e-Science Research Center, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden
| | - Christian Blau
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Solna, Sweden
| | - Marie Lycksell
- Science for Life Laboratory & Swedish e-Science Research Center, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden
| | - Rebecca Joy Howard
- Science for Life Laboratory & Swedish e-Science Research Center, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden
| | - Erik Lindahl
- Science for Life Laboratory & Swedish e-Science Research Center, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden; Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Solna, Sweden.
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4
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Blau C, Yvonnesdotter L, Lindahl E. Gentle and fast all-atom model refinement to cryo-EM densities via a maximum likelihood approach. PLoS Comput Biol 2023; 19:e1011255. [PMID: 37523411 PMCID: PMC10427019 DOI: 10.1371/journal.pcbi.1011255] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 08/15/2023] [Accepted: 06/09/2023] [Indexed: 08/02/2023] Open
Abstract
Better detectors and automated data collection have generated a flood of high-resolution cryo-EM maps, which in turn has renewed interest in improving methods for determining structure models corresponding to these maps. However, automatically fitting atoms to densities becomes difficult as their resolution increases and the refinement potential has a vast number of local minima. In practice, the problem becomes even more complex when one also wants to achieve a balance between a good fit of atom positions to the map, while also establishing good stereochemistry or allowing protein secondary structure to change during fitting. Here, we present a solution to this challenge using a maximum likelihood approach by formulating the problem as identifying the structure most likely to have produced the observed density map. This allows us to derive new types of smooth refinement potential-based on relative entropy-in combination with a novel adaptive force scaling algorithm to allow balancing of force-field and density-based potentials. In a low-noise scenario, as expected from modern cryo-EM data, the relative-entropy based refinement potential outperforms alternatives, and the adaptive force scaling appears to aid all existing refinement potentials. The method is available as a component in the GROMACS molecular simulation toolkit.
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Affiliation(s)
- Christian Blau
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Linnea Yvonnesdotter
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Erik Lindahl
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
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5
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Beton JG, Cragnolini T, Kaleel M, Mulvaney T, Sweeney A, Topf M. Integrating model simulation tools and
cryo‐electron
microscopy. WIRES COMPUTATIONAL MOLECULAR SCIENCE 2022. [DOI: 10.1002/wcms.1642] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Joseph George Beton
- Centre for Structural Systems Biology (CSSB) Leibniz‐Institut für Virologie (LIV) Hamburg Germany
| | - Tristan Cragnolini
- Institute of Structural and Molecular Biology, Birkbeck and University College London London UK
| | - Manaz Kaleel
- Centre for Structural Systems Biology (CSSB) Leibniz‐Institut für Virologie (LIV) Hamburg Germany
| | - Thomas Mulvaney
- Centre for Structural Systems Biology (CSSB) Leibniz‐Institut für Virologie (LIV) Hamburg Germany
| | - Aaron Sweeney
- Centre for Structural Systems Biology (CSSB) Leibniz‐Institut für Virologie (LIV) Hamburg Germany
| | - Maya Topf
- Centre for Structural Systems Biology (CSSB) Leibniz‐Institut für Virologie (LIV) Hamburg Germany
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6
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Alnabati E, Esquivel-Rodriguez J, Terashi G, Kihara D. MarkovFit: Structure Fitting for Protein Complexes in Electron Microscopy Maps Using Markov Random Field. Front Mol Biosci 2022; 9:935411. [PMID: 35959463 PMCID: PMC9358042 DOI: 10.3389/fmolb.2022.935411] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Accepted: 06/13/2022] [Indexed: 11/13/2022] Open
Abstract
An increasing number of protein complex structures are determined by cryo-electron microscopy (cryo-EM). When individual protein structures have been determined and are available, an important task in structure modeling is to fit the individual structures into the density map. Here, we designed a method that fits the atomic structures of proteins in cryo-EM maps of medium to low resolutions using Markov random fields, which allows probabilistic evaluation of fitted models. The accuracy of our method, MarkovFit, performed better than existing methods on datasets of 31 simulated cryo-EM maps of resolution 10 Å , nine experimentally determined cryo-EM maps of resolution less than 4 Å , and 28 experimentally determined cryo-EM maps of resolution 6 to 20 Å .
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Affiliation(s)
- Eman Alnabati
- Department of Computer Science, Purdue University, West Lafayette, IN, United States
| | | | - Genki Terashi
- Department of Biological Sciences, Purdue University, West Lafayette, IN, United States
| | - Daisuke Kihara
- Department of Computer Science, Purdue University, West Lafayette, IN, United States
- Department of Biological Sciences, Purdue University, West Lafayette, IN, United States
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7
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Warshamanage R, Yamashita K, Murshudov GN. EMDA: A Python package for Electron Microscopy Data Analysis. J Struct Biol 2021; 214:107826. [PMID: 34915128 PMCID: PMC8935390 DOI: 10.1016/j.jsb.2021.107826] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Revised: 12/01/2021] [Accepted: 12/08/2021] [Indexed: 12/01/2022]
Abstract
An open-source Python library EMDA for cryo-EM map and model manipulation is presented with a specific focus on validation. The use of several functionalities in the library is presented through several examples. The utility of local correlation as a metric for identifying map-model differences and unmodeled regions in maps, and how it is used as a metric of map-model validation is demonstrated. The mapping of local correlation to individual atoms, and its use to draw insights on local signal variations are discussed. EMDA’s likelihood-based map overlay is demonstrated by carrying out a superposition of two domains in two related structures. The overlay is carried out first to bring both maps into the same coordinate frame and then to estimate the relative movement of domains. Finally, the map magnification refinement in EMDA is presented with an example to highlight the importance of adjusting the map magnification in structural comparison studies.
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Affiliation(s)
- Rangana Warshamanage
- Structural Studies, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom.
| | - Keitaro Yamashita
- Structural Studies, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Garib N Murshudov
- Structural Studies, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom.
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8
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Simpkin AJ, Winn MD, Rigden DJ, Keegan RM. Redeployment of automated MrBUMP search-model identification for map fitting in cryo-EM. Acta Crystallogr D Struct Biol 2021; 77:1378-1385. [PMID: 34726166 PMCID: PMC8561737 DOI: 10.1107/s2059798321009165] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Accepted: 09/03/2021] [Indexed: 11/22/2022] Open
Abstract
In crystallography, the phase problem can often be addressed by the careful preparation of molecular-replacement search models. This has led to the development of pipelines such as MrBUMP that can automatically identify homologous proteins from an input sequence and edit them to focus on the areas that are most conserved. Many of these approaches can be applied directly to cryo-EM to help discover, prepare and correctly place models (here called cryo-EM search models) into electrostatic potential maps. This can significantly reduce the amount of manual model building that is required for structure determination. Here, MrBUMP is repurposed to fit automatically obtained PDB-derived chains and domains into cryo-EM maps. MrBUMP was successfully able to identify and place cryo-EM search models across a range of resolutions. Methods such as map segmentation are also explored as potential routes to improved performance. Map segmentation was also found to improve the effectiveness of the pipeline for higher resolution (<8 Å) data sets.
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Affiliation(s)
- Adam J. Simpkin
- Institute of Structural, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 7ZB, United Kingdom
| | - Martyn D. Winn
- UKRI–STFC, Rutherford Appleton Laboratory, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom
| | - Daniel J. Rigden
- Institute of Structural, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 7ZB, United Kingdom
| | - Ronan M. Keegan
- UKRI–STFC, Rutherford Appleton Laboratory, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom
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9
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Lawson CL, Kryshtafovych A, Adams PD, Afonine PV, Baker ML, Barad BA, Bond P, Burnley T, Cao R, Cheng J, Chojnowski G, Cowtan K, Dill KA, DiMaio F, Farrell DP, Fraser JS, Herzik MA, Hoh SW, Hou J, Hung LW, Igaev M, Joseph AP, Kihara D, Kumar D, Mittal S, Monastyrskyy B, Olek M, Palmer CM, Patwardhan A, Perez A, Pfab J, Pintilie GD, Richardson JS, Rosenthal PB, Sarkar D, Schäfer LU, Schmid MF, Schröder GF, Shekhar M, Si D, Singharoy A, Terashi G, Terwilliger TC, Vaiana A, Wang L, Wang Z, Wankowicz SA, Williams CJ, Winn M, Wu T, Yu X, Zhang K, Berman HM, Chiu W. Cryo-EM model validation recommendations based on outcomes of the 2019 EMDataResource challenge. Nat Methods 2021; 18:156-164. [PMID: 33542514 PMCID: PMC7864804 DOI: 10.1038/s41592-020-01051-w] [Citation(s) in RCA: 61] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 12/21/2020] [Indexed: 01/30/2023]
Abstract
This paper describes outcomes of the 2019 Cryo-EM Model Challenge. The goals were to (1) assess the quality of models that can be produced from cryogenic electron microscopy (cryo-EM) maps using current modeling software, (2) evaluate reproducibility of modeling results from different software developers and users and (3) compare performance of current metrics used for model evaluation, particularly Fit-to-Map metrics, with focus on near-atomic resolution. Our findings demonstrate the relatively high accuracy and reproducibility of cryo-EM models derived by 13 participating teams from four benchmark maps, including three forming a resolution series (1.8 to 3.1 Å). The results permit specific recommendations to be made about validating near-atomic cryo-EM structures both in the context of individual experiments and structure data archives such as the Protein Data Bank. We recommend the adoption of multiple scoring parameters to provide full and objective annotation and assessment of the model, reflective of the observed cryo-EM map density.
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Affiliation(s)
- Catherine L. Lawson
- grid.430387.b0000 0004 1936 8796Institute for Quantitative Biomedicine, Rutgers, The State University of New Jersey, Piscataway, NJ USA
| | - Andriy Kryshtafovych
- grid.27860.3b0000 0004 1936 9684Genome Center, University of California, Davis, CA USA
| | - Paul D. Adams
- grid.184769.50000 0001 2231 4551Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA USA ,grid.47840.3f0000 0001 2181 7878Department of Bioengineering, University of California Berkeley, Berkeley, CA USA
| | - Pavel V. Afonine
- grid.184769.50000 0001 2231 4551Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA USA
| | - Matthew L. Baker
- grid.267308.80000 0000 9206 2401Department of Biochemistry and Molecular Biology, The University of Texas Health Science Center at Houston, Houston, TX USA
| | - Benjamin A. Barad
- grid.214007.00000000122199231Department of Integrated Computational Structural Biology, The Scripps Research Institute, La Jolla, CA USA
| | - Paul Bond
- grid.5685.e0000 0004 1936 9668York Structural Biology Laboratory, Department of Chemistry, University of York, York, UK
| | - Tom Burnley
- grid.465239.fScientific Computing Department, UKRI Science and Technology Facilities Council, Research Complex at Harwell, Didcot, UK
| | - Renzhi Cao
- grid.261584.c0000 0001 0492 9915Department of Computer Science, Pacific Lutheran University, Tacoma, WA USA
| | - Jianlin Cheng
- grid.134936.a0000 0001 2162 3504Department of Electrical Engineering and Computer Science, University of Missouri, Columbia, MO USA
| | - Grzegorz Chojnowski
- grid.475756.20000 0004 0444 5410European Molecular Biology Laboratory, c/o DESY, Hamburg, Germany
| | - Kevin Cowtan
- grid.5685.e0000 0004 1936 9668York Structural Biology Laboratory, Department of Chemistry, University of York, York, UK
| | - Ken A. Dill
- grid.36425.360000 0001 2216 9681Laufer Center, Stony Brook University, Stony Brook, NY USA
| | - Frank DiMaio
- grid.34477.330000000122986657Department of Biochemistry and Institute for Protein Design, University of Washington, Seattle, WA USA
| | - Daniel P. Farrell
- grid.34477.330000000122986657Department of Biochemistry and Institute for Protein Design, University of Washington, Seattle, WA USA
| | - James S. Fraser
- grid.266102.10000 0001 2297 6811Department of Bioengineering and Therapeutic Sciences, University of California San Francisco, San Francisco, CA USA
| | - Mark A. Herzik
- grid.266100.30000 0001 2107 4242Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA USA
| | - Soon Wen Hoh
- grid.5685.e0000 0004 1936 9668York Structural Biology Laboratory, Department of Chemistry, University of York, York, UK
| | - Jie Hou
- grid.262962.b0000 0004 1936 9342Department of Computer Science, Saint Louis University, St. Louis, MO USA
| | - Li-Wei Hung
- grid.148313.c0000 0004 0428 3079Los Alamos National Laboratory, Los Alamos, NM USA
| | - Maxim Igaev
- grid.418140.80000 0001 2104 4211Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Agnel P. Joseph
- grid.465239.fScientific Computing Department, UKRI Science and Technology Facilities Council, Research Complex at Harwell, Didcot, UK
| | - Daisuke Kihara
- grid.169077.e0000 0004 1937 2197Department of Biological Sciences, Purdue University, West Lafayette, IN USA ,grid.169077.e0000 0004 1937 2197Department of Computer Science, Purdue University, West Lafayette, IN USA
| | - Dilip Kumar
- grid.39382.330000 0001 2160 926XVerna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX USA
| | - Sumit Mittal
- grid.215654.10000 0001 2151 2636Biodesign Institute, Arizona State University, Tempe, AZ USA ,grid.411530.20000 0001 0694 3745School of Advanced Sciences and Languages, VIT Bhopal University, Bhopal, India
| | - Bohdan Monastyrskyy
- grid.27860.3b0000 0004 1936 9684Genome Center, University of California, Davis, CA USA
| | - Mateusz Olek
- grid.5685.e0000 0004 1936 9668York Structural Biology Laboratory, Department of Chemistry, University of York, York, UK
| | - Colin M. Palmer
- grid.465239.fScientific Computing Department, UKRI Science and Technology Facilities Council, Research Complex at Harwell, Didcot, UK
| | - Ardan Patwardhan
- grid.225360.00000 0000 9709 7726The European Bioinformatics Institute (EMBL-EBI), Wellcome Genome Campus, Hinxton, UK
| | - Alberto Perez
- grid.15276.370000 0004 1936 8091Department of Chemistry, University of Florida, Gainesville, FL USA
| | - Jonas Pfab
- grid.462982.30000 0000 8883 2602Division of Computing & Software Systems, University of Washington, Bothell, WA USA
| | - Grigore D. Pintilie
- grid.168010.e0000000419368956Department of Bioengineering, Stanford University, Stanford, CA USA
| | - Jane S. Richardson
- grid.26009.3d0000 0004 1936 7961Department of Biochemistry, Duke University, Durham, NC USA
| | - Peter B. Rosenthal
- grid.451388.30000 0004 1795 1830Structural Biology of Cells and Viruses Laboratory, Francis Crick Institute, London, UK
| | - Daipayan Sarkar
- grid.169077.e0000 0004 1937 2197Department of Biological Sciences, Purdue University, West Lafayette, IN USA ,grid.215654.10000 0001 2151 2636Biodesign Institute, Arizona State University, Tempe, AZ USA
| | - Luisa U. Schäfer
- grid.8385.60000 0001 2297 375XInstitute of Biological Information Processing (IBI-7: Structural Biochemistry) and Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany
| | - Michael F. Schmid
- grid.168010.e0000000419368956Division of CryoEM and Biomaging, SSRL, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA USA
| | - Gunnar F. Schröder
- grid.8385.60000 0001 2297 375XInstitute of Biological Information Processing (IBI-7: Structural Biochemistry) and Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany ,grid.411327.20000 0001 2176 9917Physics Department, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Mrinal Shekhar
- grid.215654.10000 0001 2151 2636Biodesign Institute, Arizona State University, Tempe, AZ USA ,grid.66859.34Center for Development of Therapeutics, Broad Institute of MIT and Harvard, Cambridge, MA USA
| | - Dong Si
- grid.462982.30000 0000 8883 2602Division of Computing & Software Systems, University of Washington, Bothell, WA USA
| | - Abishek Singharoy
- grid.215654.10000 0001 2151 2636Biodesign Institute, Arizona State University, Tempe, AZ USA
| | - Genki Terashi
- grid.418140.80000 0001 2104 4211Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | | | - Andrea Vaiana
- grid.418140.80000 0001 2104 4211Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Liguo Wang
- grid.34477.330000000122986657Department of Biological Structure, University of Washington, Seattle, WA USA
| | - Zhe Wang
- grid.225360.00000 0000 9709 7726The European Bioinformatics Institute (EMBL-EBI), Wellcome Genome Campus, Hinxton, UK
| | - Stephanie A. Wankowicz
- grid.266102.10000 0001 2297 6811Department of Bioengineering and Therapeutic Sciences, University of California San Francisco, San Francisco, CA USA ,grid.266102.10000 0001 2297 6811Biophysics Graduate Program, University of California, San Francisco, CA USA
| | | | - Martyn Winn
- grid.465239.fScientific Computing Department, UKRI Science and Technology Facilities Council, Research Complex at Harwell, Didcot, UK
| | - Tianqi Wu
- grid.134936.a0000 0001 2162 3504Department of Electrical Engineering and Computer Science, University of Missouri, Columbia, MO USA
| | - Xiaodi Yu
- grid.497530.c0000 0004 0389 4927SMPS, Janssen Research and Development, Spring House, PA USA
| | - Kaiming Zhang
- grid.168010.e0000000419368956Department of Bioengineering, Stanford University, Stanford, CA USA
| | - Helen M. Berman
- grid.430387.b0000 0004 1936 8796Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ USA ,grid.42505.360000 0001 2156 6853Department of Biological Sciences and Bridge Institute, University of Southern California, Los Angeles, CA USA
| | - Wah Chiu
- grid.168010.e0000000419368956Department of Bioengineering, Stanford University, Stanford, CA USA ,grid.168010.e0000000419368956Division of CryoEM and Biomaging, SSRL, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA USA
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10
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Architecture of the flexible tail tube of bacteriophage SPP1. Nat Commun 2020; 11:5759. [PMID: 33188213 PMCID: PMC7666168 DOI: 10.1038/s41467-020-19611-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Accepted: 10/16/2020] [Indexed: 02/06/2023] Open
Abstract
Bacteriophage SPP1 is a double-stranded DNA virus of the Siphoviridae family that infects the bacterium Bacillus subtilis. This family of phages features a long, flexible, non-contractile tail that has been difficult to characterize structurally. Here, we present the atomic structure of the tail tube of phage SPP1. Our hybrid structure is based on the integration of structural restraints from solid-state nuclear magnetic resonance (NMR) and a density map from cryo-EM. We show that the tail tube protein gp17.1 organizes into hexameric rings that are stacked by flexible linker domains and, thus, form a hollow flexible tube with a negatively charged lumen suitable for the transport of DNA. Additionally, we assess the dynamics of the system by combining relaxation measurements with variances in density maps. Bacteriophages of the Siphoviridae family have a long, flexible, non-contractile tail that has been difficult to characterize structurally. Here, the authors present the atomic structure of the tail tube of one of these phages, showing a hollow flexible tube formed by hexameric rings stacked by flexible linkers.
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11
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Fisette O, Schröder GF, Schäfer LV. Atomistic structure and dynamics of the human MHC-I peptide-loading complex. Proc Natl Acad Sci U S A 2020; 117:20597-20606. [PMID: 32788370 PMCID: PMC7456110 DOI: 10.1073/pnas.2004445117] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The major histocompatibility complex class-I (MHC-I) peptide-loading complex (PLC) is a cornerstone of the human adaptive immune system, being responsible for processing antigens that allow killer T cells to distinguish between healthy and compromised cells. Based on a recent low-resolution cryo-electron microscopy (cryo-EM) structure of this large membrane-bound protein complex, we report an atomistic model of the PLC and study its conformational dynamics on the multimicrosecond time scale using all-atom molecular dynamics (MD) simulations in an explicit lipid bilayer and water environment (1.6 million atoms in total). The PLC has a layered structure, with two editing modules forming a flexible protein belt surrounding a stable, catalytically active core. Tapasin plays a central role in the PLC, stabilizing the MHC-I binding groove in a conformation reminiscent of antigen-loaded MHC-I. The MHC-I-linked glycan steers a tapasin loop involved in peptide editing toward the binding groove. Tapasin conformational dynamics are also affected by calreticulin through a conformational selection mechanism that facilitates MHC-I recruitment into the complex.
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Affiliation(s)
- Olivier Fisette
- Theoretical Chemistry, Ruhr University Bochum, D-44780 Bochum, Germany
| | - Gunnar F Schröder
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, D-52425 Jülich, Germany
- Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, D-52425 Jülich, Germany
- Physics Department, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany
| | - Lars V Schäfer
- Theoretical Chemistry, Ruhr University Bochum, D-44780 Bochum, Germany;
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12
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Gutmann T, Schäfer IB, Poojari C, Brankatschk B, Vattulainen I, Strauss M, Coskun Ü. Cryo-EM structure of the complete and ligand-saturated insulin receptor ectodomain. J Cell Biol 2020; 219:jcb.201907210. [PMID: 31727777 PMCID: PMC7039211 DOI: 10.1083/jcb.201907210] [Citation(s) in RCA: 69] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 09/19/2019] [Accepted: 10/20/2019] [Indexed: 12/20/2022] Open
Abstract
Glucose homeostasis and growth essentially depend on the hormone insulin engaging its receptor. Despite biochemical and structural advances, a fundamental contradiction has persisted in the current understanding of insulin ligand-receptor interactions. While biochemistry predicts two distinct insulin binding sites, 1 and 2, recent structural analyses have resolved only site 1. Using a combined approach of cryo-EM and atomistic molecular dynamics simulation, we present the structure of the entire dimeric insulin receptor ectodomain saturated with four insulin molecules. Complementing the previously described insulin-site 1 interaction, we present the first view of insulin bound to the discrete insulin receptor site 2. Insulin binding stabilizes the receptor ectodomain in a T-shaped conformation wherein the membrane-proximal domains converge and contact each other. These findings expand the current models of insulin binding to its receptor and of its regulation. In summary, we provide the structural basis for a comprehensive description of ligand-receptor interactions that ultimately will inform new approaches to structure-based drug design.
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Affiliation(s)
- Theresia Gutmann
- Paul Langerhans Institute Dresden of the Helmholtz Zentrum Munich at the University Hospital and Faculty of Medicine Carl Gustav Carus of Technische Universität Dresden, Dresden, Germany.,German Center for Diabetes Research, Neuherberg, Germany
| | - Ingmar B Schäfer
- Department of Structural Cell Biology, Max Planck Institute of Biochemistry, Munich, Germany
| | - Chetan Poojari
- Department of Physics, University of Helsinki, Helsinki, Finland
| | - Beate Brankatschk
- Paul Langerhans Institute Dresden of the Helmholtz Zentrum Munich at the University Hospital and Faculty of Medicine Carl Gustav Carus of Technische Universität Dresden, Dresden, Germany.,German Center for Diabetes Research, Neuherberg, Germany
| | - Ilpo Vattulainen
- Department of Physics, University of Helsinki, Helsinki, Finland.,Computational Physics Laboratory, Tampere University, Tampere, Finland
| | - Mike Strauss
- Department of Anatomy & Cell Biology, McGill University, Montreal, Quebec, Canada
| | - Ünal Coskun
- Paul Langerhans Institute Dresden of the Helmholtz Zentrum Munich at the University Hospital and Faculty of Medicine Carl Gustav Carus of Technische Universität Dresden, Dresden, Germany.,German Center for Diabetes Research, Neuherberg, Germany
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13
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Röder C, Kupreichyk T, Gremer L, Schäfer LU, Pothula KR, Ravelli RBG, Willbold D, Hoyer W, Schröder GF. Cryo-EM structure of islet amyloid polypeptide fibrils reveals similarities with amyloid-β fibrils. Nat Struct Mol Biol 2020; 27:660-667. [PMID: 32541895 DOI: 10.1101/2020.02.11.944546] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 04/30/2020] [Indexed: 05/18/2023]
Abstract
Amyloid deposits consisting of fibrillar islet amyloid polypeptide (IAPP) in pancreatic islets are associated with beta-cell loss and have been implicated in type 2 diabetes (T2D). Here, we applied cryo-EM to reconstruct densities of three dominant IAPP fibril polymorphs, formed in vitro from synthetic human IAPP. An atomic model of the main polymorph, built from a density map of 4.2-Å resolution, reveals two S-shaped, intertwined protofilaments. The segment 21-NNFGAIL-27, essential for IAPP amyloidogenicity, forms the protofilament interface together with Tyr37 and the amidated C terminus. The S-fold resembles polymorphs of Alzheimer's disease (AD)-associated amyloid-β (Aβ) fibrils, which might account for the epidemiological link between T2D and AD and reports on IAPP-Aβ cross-seeding in vivo. The results structurally link the early-onset T2D IAPP genetic polymorphism (encoding Ser20Gly) with the AD Arctic mutation (Glu22Gly) of Aβ and support the design of inhibitors and imaging probes for IAPP fibrils.
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Affiliation(s)
- Christine Röder
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany
- Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany
- Institut für Physikalische Biologie, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Tatsiana Kupreichyk
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany
- Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany
- Institut für Physikalische Biologie, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Lothar Gremer
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany
- Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany
- Institut für Physikalische Biologie, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Luisa U Schäfer
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany
- Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany
| | - Karunakar R Pothula
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany
- Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany
| | - Raimond B G Ravelli
- The Multimodal Molecular Imaging Institute, Maastricht University, Maastricht, the Netherlands
| | - Dieter Willbold
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany
- Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany
- Institut für Physikalische Biologie, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Wolfgang Hoyer
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany.
- Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany.
- Institut für Physikalische Biologie, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
| | - Gunnar F Schröder
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich, Jülich, Germany.
- Jülich Centre for Structural Biology (JuStruct), Forschungszentrum Jülich, Jülich, Germany.
- Physics Department, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
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14
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Cryo-EM structure of islet amyloid polypeptide fibrils reveals similarities with amyloid-β fibrils. Nat Struct Mol Biol 2020; 27:660-667. [PMID: 32541895 DOI: 10.1038/s41594-020-0442-4] [Citation(s) in RCA: 99] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 04/30/2020] [Indexed: 01/09/2023]
Abstract
Amyloid deposits consisting of fibrillar islet amyloid polypeptide (IAPP) in pancreatic islets are associated with beta-cell loss and have been implicated in type 2 diabetes (T2D). Here, we applied cryo-EM to reconstruct densities of three dominant IAPP fibril polymorphs, formed in vitro from synthetic human IAPP. An atomic model of the main polymorph, built from a density map of 4.2-Å resolution, reveals two S-shaped, intertwined protofilaments. The segment 21-NNFGAIL-27, essential for IAPP amyloidogenicity, forms the protofilament interface together with Tyr37 and the amidated C terminus. The S-fold resembles polymorphs of Alzheimer's disease (AD)-associated amyloid-β (Aβ) fibrils, which might account for the epidemiological link between T2D and AD and reports on IAPP-Aβ cross-seeding in vivo. The results structurally link the early-onset T2D IAPP genetic polymorphism (encoding Ser20Gly) with the AD Arctic mutation (Glu22Gly) of Aβ and support the design of inhibitors and imaging probes for IAPP fibrils.
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15
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Dodd T, Yan C, Ivanov I. Simulation-Based Methods for Model Building and Refinement in Cryoelectron Microscopy. J Chem Inf Model 2020; 60:2470-2483. [PMID: 32202798 DOI: 10.1021/acs.jcim.0c00087] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Advances in cryoelectron microscopy (cryo-EM) have revolutionized the structural investigation of large macromolecular assemblies. In this review, we first provide a broad overview of modeling methods used for flexible fitting of molecular models into cryo-EM density maps. We give special attention to approaches rooted in molecular simulations-atomistic molecular dynamics and Monte Carlo. Concise descriptions of the methods are given along with discussion of their advantages, limitations, and most popular alternatives. We also describe recent extensions of the widely used molecular dynamics flexible fitting (MDFF) method and discuss how different model-building techniques could be incorporated into new hybrid modeling schemes and simulation workflows. Finally, we provide two illustrative examples of model-building and refinement strategies employing MDFF, cascade MDFF, and RosettaCM. These examples come from recent cryo-EM studies that elucidated transcription preinitiation complexes and shed light on the functional roles of these assemblies in gene expression and gene regulation.
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Affiliation(s)
- Thomas Dodd
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.,Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30302, United States
| | - Chunli Yan
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.,Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30302, United States
| | - Ivaylo Ivanov
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.,Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30302, United States
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16
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Rout MP, Sali A. Principles for Integrative Structural Biology Studies. Cell 2020; 177:1384-1403. [PMID: 31150619 DOI: 10.1016/j.cell.2019.05.016] [Citation(s) in RCA: 165] [Impact Index Per Article: 41.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Revised: 04/24/2019] [Accepted: 05/06/2019] [Indexed: 12/22/2022]
Abstract
Integrative structure determination is a powerful approach to modeling the structures of biological systems based on data produced by multiple experimental and theoretical methods, with implications for our understanding of cellular biology and drug discovery. This Primer introduces the theory and methods of integrative approaches, emphasizing the kinds of data that can be effectively included in developing models and using the nuclear pore complex as an example to illustrate the practice and challenges involved. These guidelines are intended to aid the researcher in understanding and applying integrative structural methods to systems of their interest and thus take advantage of this rapidly evolving field.
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Affiliation(s)
- Michael P Rout
- Laboratory of Cellular and Structural Biology, The Rockefeller University, New York, NY 10065, USA.
| | - Andrej Sali
- Department of Bioengineering and Therapeutic Sciences, Department of Pharmaceutical Chemistry, California Institute for Quantitative Biosciences, Byers Hall, 1700 4th Street, Suite 503B, University of California, San Francisco, San Francisco, CA 94158, USA.
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17
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Alnabati E, Kihara D. Advances in Structure Modeling Methods for Cryo-Electron Microscopy Maps. Molecules 2019; 25:molecules25010082. [PMID: 31878333 PMCID: PMC6982917 DOI: 10.3390/molecules25010082] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Revised: 12/20/2019] [Accepted: 12/20/2019] [Indexed: 01/16/2023] Open
Abstract
Cryo-electron microscopy (cryo-EM) has now become a widely used technique for structure determination of macromolecular complexes. For modeling molecular structures from density maps of different resolutions, many algorithms have been developed. These algorithms can be categorized into rigid fitting, flexible fitting, and de novo modeling methods. It is also observed that machine learning (ML) techniques have been increasingly applied following the rapid progress of the ML field. Here, we review these different categories of macromolecule structure modeling methods and discuss their advances over time.
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Affiliation(s)
- Eman Alnabati
- Department of Computer Science, Purdue University, West Lafayette, IN 47907, USA
| | - Daisuke Kihara
- Department of Computer Science, Purdue University, West Lafayette, IN 47907, USA
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
- Correspondence:
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18
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Lawrence RE, Fromm SA, Fu Y, Yokom AL, Kim DJ, Thelen AM, Young LN, Lim CY, Samelson AJ, Hurley JH, Zoncu R. Structural mechanism of a Rag GTPase activation checkpoint by the lysosomal folliculin complex. Science 2019; 366:971-977. [PMID: 31672913 DOI: 10.1126/science.aax0364] [Citation(s) in RCA: 95] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Accepted: 10/23/2019] [Indexed: 12/16/2022]
Abstract
The tumor suppressor folliculin (FLCN) enables nutrient-dependent activation of the mechanistic target of rapamycin complex 1 (mTORC1) protein kinase via its guanosine triphosphatase (GTPase) activating protein (GAP) activity toward the GTPase RagC. Concomitant with mTORC1 inactivation by starvation, FLCN relocalizes from the cytosol to lysosomes. To determine the lysosomal function of FLCN, we reconstituted the human lysosomal FLCN complex (LFC) containing FLCN, its partner FLCN-interacting protein 2 (FNIP2), and the RagAGDP:RagCGTP GTPases as they exist in the starved state with their lysosomal anchor Ragulator complex and determined its cryo-electron microscopy structure to 3.6 angstroms. The RagC-GAP activity of FLCN was inhibited within the LFC, owing to displacement of a catalytically required arginine in FLCN from the RagC nucleotide. Disassembly of the LFC and release of the RagC-GAP activity of FLCN enabled mTORC1-dependent regulation of the master regulator of lysosomal biogenesis, transcription factor E3, implicating the LFC as a checkpoint in mTORC1 signaling.
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Affiliation(s)
- Rosalie E Lawrence
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA.,The Paul F. Glenn Center for Aging Research at the University of California, Berkeley, Berkeley, CA 94720, USA
| | - Simon A Fromm
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Yangxue Fu
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Adam L Yokom
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Do Jin Kim
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Ashley M Thelen
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA.,The Paul F. Glenn Center for Aging Research at the University of California, Berkeley, Berkeley, CA 94720, USA
| | - Lindsey N Young
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Chun-Yan Lim
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA.,The Paul F. Glenn Center for Aging Research at the University of California, Berkeley, Berkeley, CA 94720, USA
| | - Avi J Samelson
- The Paul F. Glenn Center for Aging Research at the University of California, Berkeley, Berkeley, CA 94720, USA.,Institute for Neurodegenerative Diseases, University of California at San Francisco, San Francisco, CA 94158, USA
| | - James H Hurley
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA. .,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA.,Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Roberto Zoncu
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA. .,The Paul F. Glenn Center for Aging Research at the University of California, Berkeley, Berkeley, CA 94720, USA.,California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA
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19
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Malhotra S, Träger S, Dal Peraro M, Topf M. Modelling structures in cryo-EM maps. Curr Opin Struct Biol 2019; 58:105-114. [PMID: 31394387 DOI: 10.1016/j.sbi.2019.05.024] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2019] [Revised: 05/23/2019] [Accepted: 05/25/2019] [Indexed: 12/20/2022]
Abstract
Recent advances in structure determination of sub-cellular structures using cryo-electron microscopy and tomography have enabled us to understand their architecture in a more detailed manner and gain insight into their function. The choice of approach to use for atomic model building, fitting, refinement and validation in the 3D map resulting from these experiments depends primarily on the resolution of the map and the prior information on the corresponding model. Here, we survey some of such methods and approaches and highlight their uses in specific recent examples.
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Affiliation(s)
- Sony Malhotra
- Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, United Kingdom
| | - Sylvain Träger
- Institute of Bioengineering, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, Lausanne 1015, Switzerland
| | - Matteo Dal Peraro
- Institute of Bioengineering, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, Lausanne 1015, Switzerland
| | - Maya Topf
- Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, United Kingdom.
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20
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Terashi G, Kihara D. De novo main-chain modeling for EM maps using MAINMAST. Nat Commun 2018; 9:1618. [PMID: 29691408 PMCID: PMC5915429 DOI: 10.1038/s41467-018-04053-7] [Citation(s) in RCA: 66] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Accepted: 03/29/2018] [Indexed: 11/09/2022] Open
Abstract
An increasing number of protein structures are determined by cryo-electron microscopy (cryo-EM) at near atomic resolution. However, tracing the main-chains and building full-atom models from EM maps of ~4-5 Å is still not trivial and remains a time-consuming task. Here, we introduce a fully automated de novo structure modeling method, MAINMAST, which builds three-dimensional models of a protein from a near-atomic resolution EM map. The method directly traces the protein's main-chain and identifies Cα positions as tree-graph structures in the EM map. MAINMAST performs significantly better than existing software in building global protein structure models on data sets of 40 simulated density maps at 5 Å resolution and 30 experimentally determined maps at 2.6-4.8 Å resolution. In another benchmark of building missing fragments in protein models for EM maps, MAINMAST builds fragments of 11-161 residues long with an average RMSD of 2.68 Å.
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Affiliation(s)
- Genki Terashi
- Department of Biological Sciences, Purdue University, 249S. Martin Jischke Dr., West Lafayette, IN, 47907, USA
| | - Daisuke Kihara
- Department of Biological Sciences, Purdue University, 249S. Martin Jischke Dr., West Lafayette, IN, 47907, USA. .,Department of Computer Science, Purdue University, 305N. University St., West Lafayette, IN, 47907, USA.
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21
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Kim DN, Sanbonmatsu KY. Tools for the cryo-EM gold rush: going from the cryo-EM map to the atomistic model. Biosci Rep 2017; 37:BSR20170072. [PMID: 28963369 PMCID: PMC5715128 DOI: 10.1042/bsr20170072] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Revised: 09/26/2017] [Accepted: 09/27/2017] [Indexed: 12/16/2022] Open
Abstract
As cryo-electron microscopy (cryo-EM) enters mainstream structural biology, the demand for fitting methods is high. Here, we review existing flexible fitting methods for cryo-EM. We discuss their importance, potential concerns and assessment strategies. We aim to give readers concrete descriptions of cryo-EM flexible fitting methods with corresponding examples.
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Affiliation(s)
- Doo Nam Kim
- Theoretical Biology and Biophysics Group, Los Alamos National Laboratory, Los Alamos, U.S.A
| | - Karissa Y Sanbonmatsu
- Theoretical Biology and Biophysics Group, Los Alamos National Laboratory, Los Alamos, U.S.A.
- New Mexico Consortium, Los Alamos, U.S.A
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22
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Gurel PS, Kim LY, Ruijgrok PV, Omabegho T, Bryant Z, Alushin GM. Cryo-EM structures reveal specialization at the myosin VI-actin interface and a mechanism of force sensitivity. eLife 2017; 6:e31125. [PMID: 29199952 PMCID: PMC5762158 DOI: 10.7554/elife.31125] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 12/02/2017] [Indexed: 11/30/2022] Open
Abstract
Despite extensive scrutiny of the myosin superfamily, the lack of high-resolution structures of actin-bound states has prevented a complete description of its mechanochemical cycle and limited insight into how sequence and structural diversification of the motor domain gives rise to specialized functional properties. Here we present cryo-EM structures of the unique minus-end directed myosin VI motor domain in rigor (4.6 Å) and Mg-ADP (5.5 Å) states bound to F-actin. Comparison to the myosin IIC-F-actin rigor complex reveals an almost complete lack of conservation of residues at the actin-myosin interface despite preservation of the primary sequence regions composing it, suggesting an evolutionary path for motor specialization. Additionally, analysis of the transition from ADP to rigor provides a structural rationale for force sensitivity in this step of the mechanochemical cycle. Finally, we observe reciprocal rearrangements in actin and myosin accompanying the transition between these states, supporting a role for actin structural plasticity during force generation by myosin VI.
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Affiliation(s)
- Pinar S Gurel
- Laboratory of Structural Biophysics and MechanobiologyThe Rockefeller UniversityNew YorkUnited States
- Cell Biology and Physiology CenterNational Heart, Blood, and Lung Institute, National Institutes of HealthBethesdaUnited States
| | - Laura Y Kim
- Cell Biology and Physiology CenterNational Heart, Blood, and Lung Institute, National Institutes of HealthBethesdaUnited States
| | - Paul V Ruijgrok
- Department of BioengineeringStanford UniversityStanfordUnited States
| | - Tosan Omabegho
- Department of BioengineeringStanford UniversityStanfordUnited States
| | - Zev Bryant
- Department of BioengineeringStanford UniversityStanfordUnited States
- Department of Structural BiologyStanford UniversityStanfordUnited States
| | - Gregory M Alushin
- Laboratory of Structural Biophysics and MechanobiologyThe Rockefeller UniversityNew YorkUnited States
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23
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Ismer J, Rose AS, Tiemann JKS, Hildebrand PW. A fragment based method for modeling of protein segments into cryo-EM density maps. BMC Bioinformatics 2017; 18:475. [PMID: 29132296 PMCID: PMC5683378 DOI: 10.1186/s12859-017-1904-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Accepted: 11/01/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Single-particle analysis of electron cryo-microscopy (cryo-EM) is a key technology for elucidation of macromolecular structures. Recent technical advances in hardware and software developments significantly enhanced the resolution of cryo-EM density maps and broadened the applicability and the circle of users. To facilitate modeling of macromolecules into cryo-EM density maps, fast and easy to use methods for modeling are now demanded. RESULTS Here we investigated and benchmarked the suitability of a classical and well established fragment-based approach for modeling of segments into cryo-EM density maps (termed FragFit). FragFit uses a hierarchical strategy to select fragments from a pre-calculated set of billions of fragments derived from structures deposited in the Protein Data Bank, based on sequence similarly, fit of stem atoms and fit to a cryo-EM density map. The user only has to specify the sequence of the segment and the number of the N- and C-terminal stem-residues in the protein. Using a representative data set of protein structures, we show that protein segments can be accurately modeled into cryo-EM density maps of different resolution by FragFit. Prediction quality depends on segment length, the type of secondary structure of the segment and local quality of the map. CONCLUSION Fast and automated calculation of FragFit renders it applicable for implementation of interactive web-applications e.g. to model missing segments, flexible protein parts or hinge-regions into cryo-EM density maps.
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Affiliation(s)
- Jochen Ismer
- Institute of Medical Physics and Biophysics, University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany
| | - Alexander S Rose
- Institute of Medical Physics and Biophysics, University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.,RCSB Protein Data Bank, San Diego Supercomputer Center, University of California, San Diego, CA, 92093-0743, USA
| | - Johanna K S Tiemann
- Institute of Medical Physics and Biophysics, University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.,Institute of Medical Physics and Biophysics, University Leipzig, Härtelstraße 16-18, 04107, Leipzig, Germany
| | - Peter W Hildebrand
- Institute of Medical Physics and Biophysics, University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany. .,Institute of Medical Physics and Biophysics, University Leipzig, Härtelstraße 16-18, 04107, Leipzig, Germany.
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Dou H, Burrows DW, Baker ML, Ju T. Flexible Fitting of Atomic Models into Cryo-EM Density Maps Guided by Helix Correspondences. Biophys J 2017. [PMID: 28636906 DOI: 10.1016/j.bpj.2017.04.054] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Although electron cryo-microscopy (cryo-EM) has recently achieved resolutions of better than 3 Å, at which point molecular modeling can be done directly from the density map, analysis and annotation of a cryo-EM density map still primarily rely on fitting atomic or homology models to the density map. In this article, we present, to our knowledge, a new method for flexible fitting of known or modeled protein structures into cryo-EM density maps. Unlike existing methods that are guided by local density gradients, our method is guided by correspondences between the α-helices in the density map and model, and does not require an initial rigid-body fitting step. Compared with current methods on both simulated and experimental density maps, our method not only achieves greater accuracy for proteins with large deformations but also runs as fast or faster than many of the other flexible fitting routines.
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Affiliation(s)
- Hang Dou
- Department of Computer Science and Engineering, Washington University in St. Louis, St. Louis, Missouri.
| | - Derek W Burrows
- Department of Computer Science and Engineering, Washington University in St. Louis, St. Louis, Missouri
| | - Matthew L Baker
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas
| | - Tao Ju
- Department of Computer Science and Engineering, Washington University in St. Louis, St. Louis, Missouri
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25
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Joseph AP, Lagerstedt I, Patwardhan A, Topf M, Winn M. Improved metrics for comparing structures of macromolecular assemblies determined by 3D electron-microscopy. J Struct Biol 2017; 199:12-26. [PMID: 28552721 PMCID: PMC5479444 DOI: 10.1016/j.jsb.2017.05.007] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2016] [Revised: 05/19/2017] [Accepted: 05/23/2017] [Indexed: 11/28/2022]
Abstract
Recent developments in 3-dimensional electron microcopy (3D-EM) techniques and a concomitant drive to look at complex molecular structures, have led to a rapid increase in the amount of volume data available for biomolecules. This creates a demand for better methods to analyse the data, including improved scores for comparison, classification and integration of data at different resolutions. To this end, we developed and evaluated a set of scoring functions that compare 3D-EM volumes. To test our scores we used a benchmark set of volume alignments derived from the Electron Microscopy Data Bank. We find that the performance of different scores vary with the map-type, resolution and the extent of overlap between volumes. Importantly, adding the overlap information to the local scoring functions can significantly improve their precision and accuracy in a range of resolutions. A combined score involving the local mutual information and overlap (LMI_OV) performs best overall, irrespective of the map category, resolution or the extent of overlap, and we recommend this score for general use. The local mutual information score itself is found to be more discriminatory than cross-correlation coefficient for intermediate-to-low resolution maps or when the map size and density distribution differ significantly. For comparing map surfaces, we implemented two filters to detect the surface points, including one based on the 'extent of surface exposure'. We show that scores that compare surfaces are useful at low resolutions and for maps with evident surface features. All the scores discussed are implemented in TEMPy (http://tempy.ismb.lon.ac.uk/).
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Affiliation(s)
- Agnel Praveen Joseph
- Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, United Kingdom; Scientific Computing Department, Science and Technology Facilities Council, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom
| | - Ingvar Lagerstedt
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Genome Campus, Hinxton, Cambridge CB10 1SD, United Kingdom; Computational Chemistry and Cheminformatics, Lilly UK, Windlesham GU20 6PH, United Kingdom
| | - Ardan Patwardhan
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Genome Campus, Hinxton, Cambridge CB10 1SD, United Kingdom
| | - Maya Topf
- Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, United Kingdom.
| | - Martyn Winn
- Scientific Computing Department, Science and Technology Facilities Council, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom.
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26
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Merino F, Raunser S. Kryo-Elektronenmikroskopie als Methode für die strukturbasierte Wirkstoffentwicklung. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201608432] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Felipe Merino
- Strukturelle Biochemie; Max-Planck-Institut für Molekulare Physiologie; 44227 Dortmund Deutschland
| | - Stefan Raunser
- Strukturelle Biochemie; Max-Planck-Institut für Molekulare Physiologie; 44227 Dortmund Deutschland
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27
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Merino F, Raunser S. Electron Cryo-microscopy as a Tool for Structure-Based Drug Development. Angew Chem Int Ed Engl 2017; 56:2846-2860. [PMID: 27860084 DOI: 10.1002/anie.201608432] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Indexed: 12/15/2022]
Abstract
For decades, X-ray crystallography and NMR have been the most important techniques for studying the atomic structure of macromolecules. However, as a result of size, instability, low yield, and other factors, many macromolecules are difficult to crystallize or unsuitable for NMR studies. Electron cryo-microscopy (cryo-EM) does not depend on crystals and has therefore been the method of choice for many macromolecular complexes that cannot be crystallized, but atomic resolution has mostly been beyond its reach. A new generation of detectors that are capable of sensing directly the incident electrons has recently revolutionized the field, with structures of macromolecules now routinely being solved to near-atomic resolution. In this review, we summarize some of the most recent examples of high-resolution cryo-EM structures. We put particular emphasis on proteins with pharmacological relevance that have traditionally been inaccessible to crystallography. Furthermore, we discuss examples where interactions with small molecules have been fully characterized at atomic resolution. Finally, we stress the current limits of cryo-EM, and methodological issues related to its usage as a tool for drug development.
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Affiliation(s)
- Felipe Merino
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227, Dortmund, Germany
| | - Stefan Raunser
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227, Dortmund, Germany
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28
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The Central domain of RyR1 is the transducer for long-range allosteric gating of channel opening. Cell Res 2016; 26:995-1006. [PMID: 27468892 PMCID: PMC5034110 DOI: 10.1038/cr.2016.89] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Revised: 07/06/2016] [Accepted: 07/06/2016] [Indexed: 12/18/2022] Open
Abstract
The ryanodine receptors (RyRs) are intracellular calcium channels responsible for rapid release of Ca2+ from the sarcoplasmic/endoplasmic reticulum (SR/ER) to the cytoplasm, which is essential for the excitation-contraction (E-C) coupling of cardiac and skeletal muscles. The near-atomic resolution structure of closed RyR1 revealed the molecular details of this colossal channel, while the long-range allosteric gating mechanism awaits elucidation. Here, we report the cryo-EM structures of rabbit RyR1 in three closed conformations at about 4 Å resolution and an open state at 5.7 Å. Comparison of the closed RyR1 structures shows a breathing motion of the cytoplasmic platform, while the channel domain and its contiguous Central domain remain nearly unchanged. Comparison of the open and closed structures shows a dilation of the S6 tetrahelical bundle at the cytoplasmic gate that leads to channel opening. During the pore opening, the cytoplasmic “O-ring” motif of the channel domain and the U-motif of the Central domain exhibit coupled motion, while the Central domain undergoes domain-wise displacement. These structural analyses provide important insight into the E-C coupling in skeletal muscles and identify the Central domain as the transducer that couples the conformational changes of the cytoplasmic platform to the gating of the central pore.
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29
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Joseph AP, Malhotra S, Burnley T, Wood C, Clare DK, Winn M, Topf M. Refinement of atomic models in high resolution EM reconstructions using Flex-EM and local assessment. Methods 2016; 100:42-9. [PMID: 26988127 PMCID: PMC4854230 DOI: 10.1016/j.ymeth.2016.03.007] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Revised: 03/09/2016] [Accepted: 03/14/2016] [Indexed: 01/19/2023] Open
Abstract
As the resolutions of Three Dimensional Electron Microscopic reconstructions of biological macromolecules are being improved, there is a need for better fitting and refinement methods at high resolutions and robust approaches for model assessment. Flex-EM/MODELLER has been used for flexible fitting of atomic models in intermediate-to-low resolution density maps of different biological systems. Here, we demonstrate the suitability of the method to successfully refine structures at higher resolutions (2.5-4.5Å) using both simulated and experimental data, including a newly processed map of Apo-GroEL. A hierarchical refinement protocol was adopted where the rigid body definitions are relaxed and atom displacement steps are reduced progressively at successive stages of refinement. For the assessment of local fit, we used the SMOC (segment-based Manders' overlap coefficient) score, while the model quality was checked using the Qmean score. Comparison of SMOC profiles at different stages of refinement helped in detecting regions that are poorly fitted. We also show how initial model errors can have significant impact on the goodness-of-fit. Finally, we discuss the implementation of Flex-EM in the CCP-EM software suite.
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Affiliation(s)
- Agnel Praveen Joseph
- Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, United Kingdom
| | - Sony Malhotra
- Scientific Computing Department, Science and Technology Facilities Council, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom
| | - Tom Burnley
- Scientific Computing Department, Science and Technology Facilities Council, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom
| | - Chris Wood
- Scientific Computing Department, Science and Technology Facilities Council, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom
| | - Daniel K Clare
- Electron Bio-Imaging Centre (eBIC), Diamond Light Source, Harwell Science & Innovation Campus, OX11 0DE, United Kingdom
| | - Martyn Winn
- Scientific Computing Department, Science and Technology Facilities Council, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom.
| | - Maya Topf
- Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, United Kingdom.
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Kirmizialtin S, Loerke J, Behrmann E, Spahn CMT, Sanbonmatsu KY. Using Molecular Simulation to Model High-Resolution Cryo-EM Reconstructions. Methods Enzymol 2015; 558:497-514. [PMID: 26068751 DOI: 10.1016/bs.mie.2015.02.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
An explosion of new data from high-resolution cryo-electron microscopy (cryo-EM) studies has produced a large number of data sets for many species of ribosomes in various functional states over the past few years. While many methods exist to produce structural models for lower resolution cryo-EM reconstructions, high-resolution reconstructions are often modeled using crystallographic techniques and extensive manual intervention. Here, we present an automated fitting technique for high-resolution cryo-EM data sets that produces all-atom models highly consistent with the EM density. Using a molecular dynamics approach, atomic positions are optimized with a potential that includes the cross-correlation coefficient between the structural model and the cryo-EM electron density, as well as a biasing potential preserving the stereochemistry and secondary structure of the biomolecule. Specifically, we use a hybrid structure-based/ab initio molecular dynamics potential to extend molecular dynamics fitting. In addition, we find that simulated annealing integration, as opposed to straightforward molecular dynamics integration, significantly improves performance. We obtain atomistic models of the human ribosome consistent with high-resolution cryo-EM reconstructions of the human ribosome. Automated methods such as these have the potential to produce atomistic models for a large number of ribosome complexes simultaneously that can be subsequently refined manually.
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Affiliation(s)
- Serdal Kirmizialtin
- Department of Chemistry, New York University, Abu Dhabi, United Arab Emirates; New Mexico Consortium, Los Alamos, New Mexico, USA; Theoretical Biology and Biophysics, Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, USA
| | - Justus Loerke
- Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Elmar Behrmann
- Structural Dynamics of Proteins, Center of Advanced European Studies and Research (CAESAR), Bonn, Germany
| | - Christian M T Spahn
- Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Karissa Y Sanbonmatsu
- New Mexico Consortium, Los Alamos, New Mexico, USA; Theoretical Biology and Biophysics, Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, USA.
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31
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Schröder GF. Hybrid methods for macromolecular structure determination: experiment with expectations. Curr Opin Struct Biol 2015; 31:20-7. [DOI: 10.1016/j.sbi.2015.02.016] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Revised: 02/22/2015] [Accepted: 02/26/2015] [Indexed: 12/15/2022]
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32
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Tamò GE, Abriata LA, Dal Peraro M. The importance of dynamics in integrative modeling of supramolecular assemblies. Curr Opin Struct Biol 2015; 31:28-34. [PMID: 25795087 DOI: 10.1016/j.sbi.2015.02.018] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Revised: 02/10/2015] [Accepted: 02/26/2015] [Indexed: 11/16/2022]
Abstract
Revealing the atomistic architecture of supramolecular complexes is a fundamental step toward a deeper understanding of cellular functioning. To date, this formidable task is facilitated by an emerging array of integrative modeling approaches that combine experimental data from different sources. One major challenge these methods have to face is the treatment of the dynamic rearrangements of the individual subunits upon assembly. While this flexibility can be sampled at different levels, integrating native dynamic determinants with available experimental inputs can provide an effective way to reveal the molecular recognition mechanisms at the basis of supramolecular assembly.
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Affiliation(s)
- Giorgio E Tamò
- Laboratory for Biomolecular Modeling, Institute of Bioengineering, School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL) and Swiss Institute of Bioinformatics (SIB), Lausanne, Switzerland
| | - Luciano A Abriata
- Laboratory for Biomolecular Modeling, Institute of Bioengineering, School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL) and Swiss Institute of Bioinformatics (SIB), Lausanne, Switzerland
| | - Matteo Dal Peraro
- Laboratory for Biomolecular Modeling, Institute of Bioengineering, School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL) and Swiss Institute of Bioinformatics (SIB), Lausanne, Switzerland.
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33
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Uchimura S, Fujii T, Takazaki H, Ayukawa R, Nishikawa Y, Minoura I, Hachikubo Y, Kurisu G, Sutoh K, Kon T, Namba K, Muto E. A flipped ion pair at the dynein-microtubule interface is critical for dynein motility and ATPase activation. ACTA ACUST UNITED AC 2015; 208:211-22. [PMID: 25583999 PMCID: PMC4298687 DOI: 10.1083/jcb.201407039] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Dynein is a motor protein that moves on microtubules (MTs) using the energy of adenosine triphosphate (ATP) hydrolysis. To understand its motility mechanism, it is crucial to know how the signal of MT binding is transmitted to the ATPase domain to enhance ATP hydrolysis. However, the molecular basis of signal transmission at the dynein-MT interface remains unclear. Scanning mutagenesis of tubulin identified two residues in α-tubulin, R403 and E416, that are critical for ATPase activation and directional movement of dynein. Electron cryomicroscopy and biochemical analyses revealed that these residues form salt bridges with the residues in the dynein MT-binding domain (MTBD) that work in concert to induce registry change in the stalk coiled coil and activate the ATPase. The R403-E3390 salt bridge functions as a switch for this mechanism because of its reversed charge relative to other residues at the interface. This study unveils the structural basis for coupling between MT binding and ATPase activation and implicates the MTBD in the control of directional movement.
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Affiliation(s)
- Seiichi Uchimura
- Laboratory for Molecular Biophysics, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan
| | - Takashi Fujii
- Graduate School of Frontier Biosciences and Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology, Kawaguchi, Saitama 332-0012, Japan Quantitative Biology Center, Institute of Physical and Chemical Research, Suita, Osaka 565-0871, Japan
| | - Hiroko Takazaki
- Laboratory for Molecular Biophysics, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan
| | - Rie Ayukawa
- Laboratory for Molecular Biophysics, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan
| | - Yosuke Nishikawa
- Graduate School of Frontier Biosciences and Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Itsushi Minoura
- Laboratory for Molecular Biophysics, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan
| | - You Hachikubo
- Laboratory for Molecular Biophysics, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan
| | - Genji Kurisu
- Graduate School of Frontier Biosciences and Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Kazuo Sutoh
- Research Institute for Science and Engineering, Waseda University, Toshima-ku, Tokyo 171-0033, Japan
| | - Takahide Kon
- Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology, Kawaguchi, Saitama 332-0012, Japan Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Department of Frontier Bioscience, Faculty of Bioscience and Applied Chemistry, Hosei University, Koganei, Tokyo 184-8584, Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences and Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan Quantitative Biology Center, Institute of Physical and Chemical Research, Suita, Osaka 565-0871, Japan
| | - Etsuko Muto
- Laboratory for Molecular Biophysics, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan
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Brown A, Long F, Nicholls RA, Toots J, Emsley P, Murshudov G. Tools for macromolecular model building and refinement into electron cryo-microscopy reconstructions. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2015; 71:136-53. [PMID: 25615868 PMCID: PMC4304694 DOI: 10.1107/s1399004714021683] [Citation(s) in RCA: 431] [Impact Index Per Article: 47.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Accepted: 10/01/2014] [Indexed: 11/24/2022]
Abstract
The recent rapid development of single-particle electron cryo-microscopy (cryo-EM) now allows structures to be solved by this method at resolutions close to 3 Å. Here, a number of tools to facilitate the interpretation of EM reconstructions with stereochemically reasonable all-atom models are described. The BALBES database has been repurposed as a tool for identifying protein folds from density maps. Modifications to Coot, including new Jiggle Fit and morphing tools and improved handling of nucleic acids, enhance its functionality for interpreting EM maps. REFMAC has been modified for optimal fitting of atomic models into EM maps. As external structural information can enhance the reliability of the derived atomic models, stabilize refinement and reduce overfitting, ProSMART has been extended to generate interatomic distance restraints from nucleic acid reference structures, and a new tool, LIBG, has been developed to generate nucleic acid base-pair and parallel-plane restraints. Furthermore, restraint generation has been integrated with visualization and editing in Coot, and these restraints have been applied to both real-space refinement in Coot and reciprocal-space refinement in REFMAC.
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Affiliation(s)
- Alan Brown
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, England
| | - Fei Long
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, England
| | - Robert A. Nicholls
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, England
| | - Jaan Toots
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, England
| | - Paul Emsley
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, England
| | - Garib Murshudov
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, England
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35
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Structure of the F-actin-tropomyosin complex. Nature 2014; 519:114-7. [PMID: 25470062 DOI: 10.1038/nature14033] [Citation(s) in RCA: 283] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Accepted: 11/07/2014] [Indexed: 12/11/2022]
Abstract
Filamentous actin (F-actin) is the major protein of muscle thin filaments, and actin microfilaments are the main component of the eukaryotic cytoskeleton. Mutations in different actin isoforms lead to early-onset autosomal dominant non-syndromic hearing loss, familial thoracic aortic aneurysms and dissections, and multiple variations of myopathies. In striated muscle fibres, the binding of myosin motors to actin filaments is mainly regulated by tropomyosin and troponin. Tropomyosin also binds to F-actin in smooth muscle and in non-muscle cells and stabilizes and regulates the filaments there in the absence of troponin. Although crystal structures for monomeric actin (G-actin) are available, a high-resolution structure of F-actin is still missing, hampering our understanding of how disease-causing mutations affect the function of thin muscle filaments and microfilaments. Here we report the three-dimensional structure of F-actin at a resolution of 3.7 Å in complex with tropomyosin at a resolution of 6.5 Å, determined by electron cryomicroscopy. The structure reveals that the D-loop is ordered and acts as a central region for hydrophobic and electrostatic interactions that stabilize the F-actin filament. We clearly identify map density corresponding to ADP and Mg(2+) and explain the possible effect of prominent disease-causing mutants. A comparison of F-actin with G-actin reveals the conformational changes during filament formation and identifies the D-loop as their key mediator. We also confirm that negatively charged tropomyosin interacts with a positively charged groove on F-actin. Comparison of the position of tropomyosin in F-actin-tropomyosin with its position in our previously determined F-actin-tropomyosin-myosin structure reveals a myosin-induced transition of tropomyosin. Our results allow us to understand the role of individual mutations in the genesis of actin- and tropomyosin-related diseases and will serve as a strong foundation for the targeted development of drugs.
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Schröder GF, Levitt M, Brunger AT. Deformable elastic network refinement for low-resolution macromolecular crystallography. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2014; 70:2241-55. [PMID: 25195739 PMCID: PMC4157441 DOI: 10.1107/s1399004714016496] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 07/16/2014] [Indexed: 11/16/2022]
Abstract
Crystals of membrane proteins and protein complexes often diffract to low resolution owing to their intrinsic molecular flexibility, heterogeneity or the mosaic spread of micro-domains. At low resolution, the building and refinement of atomic models is a more challenging task. The deformable elastic network (DEN) refinement method developed previously has been instrumental in the determinion of several structures at low resolution. Here, DEN refinement is reviewed, recommendations for its optimal usage are provided and its limitations are discussed. Representative examples of the application of DEN refinement to challenging cases of refinement at low resolution are presented. These cases include soluble as well as membrane proteins determined at limiting resolutions ranging from 3 to 7 Å. Potential extensions of the DEN refinement technique and future perspectives for the interpretation of low-resolution crystal structures are also discussed.
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Affiliation(s)
- Gunnar F. Schröder
- Institute of Complex Systems (ICS-6), Forschungszentrum Jülich, 52425 Jülich, Germany
- Physics Department, Heinrich-Heine University Düsseldorf, 20225 Düsseldorf, Germany
| | - Michael Levitt
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Axel T. Brunger
- Howard Hughes Medical Institute and Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science, Stanford University School of Medicine, J. H. Clark Center, 318 Campus Drive, Stanford, CA 94305, USA
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Song F, Chen P, Sun D, Wang M, Dong L, Liang D, Xu RM, Zhu P, Li G. Cryo-EM study of the chromatin fiber reveals a double helix twisted by tetranucleosomal units. Science 2014; 344:376-80. [PMID: 24763583 DOI: 10.1126/science.1251413] [Citation(s) in RCA: 424] [Impact Index Per Article: 42.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The hierarchical packaging of eukaryotic chromatin plays a central role in transcriptional regulation and other DNA-related biological processes. Here, we report the 11-angstrom-resolution cryogenic electron microscopy (cryo-EM) structures of 30-nanometer chromatin fibers reconstituted in the presence of linker histone H1 and with different nucleosome repeat lengths. The structures show a histone H1-dependent left-handed twist of the repeating tetranucleosomal structural units, within which the four nucleosomes zigzag back and forth with a straight linker DNA. The asymmetric binding and the location of histone H1 in chromatin play a role in the formation of the 30-nanometer fiber. Our results provide mechanistic insights into how nucleosomes compact into higher-order chromatin fibers.
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Affiliation(s)
- Feng Song
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
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38
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Mechanism of Tc toxin action revealed in molecular detail. Nature 2014; 508:61-5. [DOI: 10.1038/nature13015] [Citation(s) in RCA: 121] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Accepted: 01/10/2014] [Indexed: 12/20/2022]
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39
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iMODFIT: efficient and robust flexible fitting based on vibrational analysis in internal coordinates. J Struct Biol 2013; 184:261-70. [PMID: 23999189 DOI: 10.1016/j.jsb.2013.08.010] [Citation(s) in RCA: 127] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 08/20/2013] [Accepted: 08/22/2013] [Indexed: 12/31/2022]
Abstract
Here, we employed the collective motions extracted from Normal Mode Analysis (NMA) in internal coordinates (torsional space) for the flexible fitting of atomic-resolution structures into electron microscopy (EM) density maps. The proposed methodology was validated using a benchmark of simulated cases, highlighting its robustness over the full range of EM resolutions and even over coarse-grained representations. A systematic comparison with other methods further showcased the advantages of this proposed methodology, especially at medium to lower resolutions. Using this method, computational costs and potential overfitting problems are naturally reduced by constraining the search in low-frequency NMA space, where covalent geometry is implicitly maintained. This method also effectively captures the macromolecular changes of a representative set of experimental test cases. We believe that this novel approach will extend the currently available EM hybrid methods to the atomic-level interpretation of large conformational changes and their functional implications.
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Esquivel-Rodríguez J, Kihara D. Computational methods for constructing protein structure models from 3D electron microscopy maps. J Struct Biol 2013; 184:93-102. [PMID: 23796504 DOI: 10.1016/j.jsb.2013.06.008] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 06/11/2013] [Accepted: 06/13/2013] [Indexed: 12/31/2022]
Abstract
Protein structure determination by cryo-electron microscopy (EM) has made significant progress in the past decades. Resolutions of EM maps have been improving as evidenced by recently reported structures that are solved at high resolutions close to 3Å. Computational methods play a key role in interpreting EM data. Among many computational procedures applied to an EM map to obtain protein structure information, in this article we focus on reviewing computational methods that model protein three-dimensional (3D) structures from a 3D EM density map that is constructed from two-dimensional (2D) maps. The computational methods we discuss range from de novo methods, which identify structural elements in an EM map, to structure fitting methods, where known high resolution structures are fit into a low-resolution EM map. A list of available computational tools is also provided.
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Affiliation(s)
- Juan Esquivel-Rodríguez
- Department of Computer Science, College of Science, Purdue University, West Lafayette, IN 47907, USA
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41
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Rodgers TL, Burnell D, Townsend PD, Pohl E, Cann MJ, Wilson MR, McLeish TCB. ΔΔPT: a comprehensive toolbox for the analysis of protein motion. BMC Bioinformatics 2013; 14:183. [PMID: 23758746 PMCID: PMC3689072 DOI: 10.1186/1471-2105-14-183] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Accepted: 05/24/2013] [Indexed: 11/30/2022] Open
Abstract
Background Normal Mode Analysis is one of the most successful techniques for studying motions in proteins and macromolecules. It can provide information on the mechanism of protein functions, used to aid crystallography and NMR data reconstruction, and calculate protein free energies. Results ΔΔPT is a toolbox allowing calculation of elastic network models and principle component analysis. It allows the analysis of pdb files or trajectories taken from; Gromacs, Amber, and DL_POLY. As well as calculation of the normal modes it also allows comparison of the modes with experimental protein motion, variation of modes with mutation or ligand binding, and calculation of molecular dynamic entropies. Conclusions This toolbox makes the respective tools available to a wide community of potential NMA users, and allows them unrivalled ability to analyse normal modes using a variety of techniques and current software.
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Deng X, Morris J, Chaton C, Schröder GF, Davidson WS, Thompson TB. Small-angle X-ray scattering of apolipoprotein A-IV reveals the importance of its termini for structural stability. J Biol Chem 2013; 288:4854-66. [PMID: 23288849 PMCID: PMC3576090 DOI: 10.1074/jbc.m112.436709] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Revised: 01/02/2013] [Indexed: 12/25/2022] Open
Abstract
ApoA-IV is an amphipathic protein that can emulsify lipids and has been linked to protective roles against cardiovascular disease and obesity. We previously reported an x-ray crystal structure of apoA-IV that was truncated at its N and C termini. Here, we have extended this work by demonstrating that self-associated states of apoA-IV are stable and can be structurally studied using small-angle x-ray scattering. Both the full-length monomeric and dimeric forms of apoA-IV were examined, with the dimer showing an elongated rod core with two nodes at opposing ends. The monomer is roughly half the length of the dimer with a single node. Small-angle x-ray scattering visualization of several deletion mutants revealed that removal of both termini can have substantial conformational effects throughout the molecule. Additionally, the F334A point mutation, which we previously showed increases apoA-IV lipid binding, also exhibited large conformational effects on the entire dimer. Merging this study's low-resolution structural information with the crystal structure provides insight on the conformation of apoA-IV as a monomer and as a dimer and further defines that a clasp mechanism may control lipid binding and, ultimately, protein function.
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Affiliation(s)
- Xiaodi Deng
- From the Department of Molecular Genetics, Biochemistry, and Microbiology, College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267
| | - Jamie Morris
- the Department of Pathology and Laboratory Medicine, College of Medicine, Metabolic Diseases Institute, University of Cincinnati, Cincinnati, Ohio 45215, and
| | - Catherine Chaton
- From the Department of Molecular Genetics, Biochemistry, and Microbiology, College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267
| | - Gunnar F. Schröder
- the Institute of Complex Systems (ICS-6), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - W. Sean Davidson
- the Department of Pathology and Laboratory Medicine, College of Medicine, Metabolic Diseases Institute, University of Cincinnati, Cincinnati, Ohio 45215, and
| | - Thomas B. Thompson
- From the Department of Molecular Genetics, Biochemistry, and Microbiology, College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267
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Consensus among multiple approaches as a reliability measure for flexible fitting into cryo-EM data. J Struct Biol 2013; 182:67-77. [PMID: 23416197 DOI: 10.1016/j.jsb.2013.02.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2012] [Revised: 01/29/2013] [Accepted: 02/01/2013] [Indexed: 12/14/2022]
Abstract
Cryo-electron microscopy (cryo-EM) can provide low-resolution density maps of large macromolecular assemblies. As the number of structures deposited in the Protein Data Bank by fitting a high-resolution structure into a low-resolution cryo-EM map is increasing, there is a need to revise the protocols and improve the measures for fitting. A recent study suggested using a combination of multiple automated flexible fitting approaches to improve the interpretation of cryo-EM data. The current work further explores the use of multiple approaches by validating this "consensus" fitting approach and deriving a local reliability measure. Here four different flexible fitting approaches are applied for fitting an initial structure into a simulated density map of known target structure from a dataset of proteins. It is found that the models produced from different approaches often have a consensus in conformation and are also near to the target structure, whereas cases not showing consensus are away from the target. A high correlation is also observed between the RMSF profiles calculated with respect to the average and the target structures, which indicates that the relation between consensus and accuracy can also be extended to a per-residue level. Therefore, the RMSF among the fitted models is proposed as a local reliability measure, which can be used to assess the reliability of the fit at specific regions. Hence, we encourage the community to use consensus flexible fitting with different methods to report on local reliability of the resulting models and improve the interpretation of cryo-EM data.
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Atomic modeling of cryo-electron microscopy reconstructions--joint refinement of model and imaging parameters. J Struct Biol 2013; 182:10-21. [PMID: 23376441 DOI: 10.1016/j.jsb.2013.01.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Revised: 12/20/2012] [Accepted: 01/11/2013] [Indexed: 11/22/2022]
Abstract
When refining the fit of component atomic structures into electron microscopic reconstructions, use of a resolution-dependent atomic density function makes it possible to jointly optimize the atomic model and imaging parameters of the microscope. Atomic density is calculated by one-dimensional Fourier transform of atomic form factors convoluted with a microscope envelope correction and a low-pass filter, allowing refinement of imaging parameters such as resolution, by optimizing the agreement of calculated and experimental maps. A similar approach allows refinement of atomic displacement parameters, providing indications of molecular flexibility even at low resolution. A modest improvement in atomic coordinates is possible following optimization of these additional parameters. Methods have been implemented in a Python program that can be used in stand-alone mode for rigid-group refinement, or embedded in other optimizers for flexible refinement with stereochemical restraints. The approach is demonstrated with refinements of virus and chaperonin structures at resolutions of 9 through 4.5 Å, representing regimes where rigid-group and fully flexible parameterizations are appropriate. Through comparisons to known crystal structures, flexible fitting by RSRef is shown to be an improvement relative to other methods and to generate models with all-atom rms accuracies of 1.5-2.5 Å at resolutions of 4.5-6 Å.
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