51
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Zhang Y, Tammaro R, Peters P, Ravelli R. Could Egg White Lysozyme be Solved by Single Particle Cryo-EM? J Chem Inf Model 2020; 60:2605-2613. [PMID: 32202786 PMCID: PMC7254834 DOI: 10.1021/acs.jcim.9b01176] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Indexed: 12/29/2022]
Abstract
The combination of high-end cryogenic transmission electron microscopes (cryo-EM), direct electron detectors, and advanced image algorithms allows researchers to obtain the 3D structures of much smaller macromolecules than years ago. However, there are still major challenges for the single-particle cryo-EM method to achieve routine structure determinations for macromolecules much smaller than 100 kDa, which are the majority of all plant and animal proteins. These challenges include sample characteristics such as sample heterogeneity, beam damage, ice layer thickness, stability, and quality, as well as hardware limitations such as detector performance, beam, and phase plate quality. Here, single particle data sets were simulated for samples that were ideal in terms of homogeneity, distribution, and stability, but with realistic parameters for ice layer, dose, detector performance, and beam characteristics. Reference data were calculated for human apo-ferritin using identical parameters reported for an experimental data set downloaded from EMPIAR. Processing of the simulated data set resulted in a value of 1.86 Å from 20 214 particles, similar to a 2 Å density map obtained from 29 224 particles selected from real micrographs. Simulated data sets were then generated for a 14 kDa protein, hen egg white lysozyme (HEWL), with and without an ideal phase plate (PP). Whereas we could not obtain a high-resolution 3D reconstruction of HEWL for the data set without PP, the one with PP resulted in a 2.78 Å resolution density map from 225 751 particles. Our simulator and simulations could help in pushing the size limits of cryo-EM.
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Affiliation(s)
- Y. Zhang
- The Maastricht Multimodal
Molecular Imaging Institute (M4I), Division of Nanoscopy, Maastricht University, 6229ER, Maastricht, The Netherlands
| | - R. Tammaro
- The Maastricht Multimodal
Molecular Imaging Institute (M4I), Division of Nanoscopy, Maastricht University, 6229ER, Maastricht, The Netherlands
| | - P.J. Peters
- The Maastricht Multimodal
Molecular Imaging Institute (M4I), Division of Nanoscopy, Maastricht University, 6229ER, Maastricht, The Netherlands
| | - R.B.G. Ravelli
- The Maastricht Multimodal
Molecular Imaging Institute (M4I), Division of Nanoscopy, Maastricht University, 6229ER, Maastricht, The Netherlands
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52
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Robertson MJ, van Zundert GCP, Borrelli K, Skiniotis G. GemSpot: A Pipeline for Robust Modeling of Ligands into Cryo-EM Maps. Structure 2020; 28:707-716.e3. [PMID: 32413291 DOI: 10.1016/j.str.2020.04.018] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2019] [Revised: 02/13/2020] [Accepted: 04/22/2020] [Indexed: 12/20/2022]
Abstract
Producing an accurate atomic model of biomolecule-ligand interactions from maps generated by cryoelectron microscopy (cryo-EM) often presents challenges inherent to the methodology and the dynamic nature of ligand binding. Here, we present GemSpot, an automated pipeline of computational chemistry methods that take into account EM map potentials, quantum mechanics energy calculations, and water molecule site prediction to generate candidate poses and provide a measure of the degree of confidence. The pipeline is validated through several published cryo-EM structures of complexes in different resolution ranges and various types of ligands. In all cases, at least one identified pose produced both excellent interactions with the target and agreement with the map. GemSpot will be valuable for the robust identification of ligand poses and drug discovery efforts through cryo-EM.
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Affiliation(s)
- Michael J Robertson
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | | | | | - Georgios Skiniotis
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
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53
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Beckers M, Palmer CM, Sachse C. Confidence maps: statistical inference of cryo-EM maps. Acta Crystallogr D Struct Biol 2020; 76:332-339. [PMID: 32254057 PMCID: PMC7137106 DOI: 10.1107/s2059798320002995] [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: 12/03/2019] [Accepted: 03/03/2020] [Indexed: 11/11/2022] Open
Abstract
Confidence maps provide complementary information for interpreting cryo-EM densities as they indicate statistical significance with respect to background noise. They can be thresholded by specifying the expected false-discovery rate (FDR), and the displayed volume shows the parts of the map that have the corresponding level of significance. Here, the basic statistical concepts of confidence maps are reviewed and practical guidance is provided for their interpretation and usage inside the CCP-EM suite. Limitations of the approach are discussed and extensions towards other error criteria such as the family-wise error rate are presented. The observed map features can be rendered at a common isosurface threshold, which is particularly beneficial for the interpretation of weak and noisy densities. In the current article, a practical guide is provided to the recommended usage of confidence maps.
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Affiliation(s)
- Maximilian Beckers
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Colin M. Palmer
- Scientific Computing Department, Science and Technology Facilities Council, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom
| | - Carsten Sachse
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
- Ernst-Ruska Centre for Microscopy and Spectroscopy with Electrons 3/Structural Biology, Forschungszentrum Jülich, 52425 Jülich, Germany
- JuStruct: Jülich Center for Structural Biology, Forschungszentrum Jülich, 52425 Jülich, Germany
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54
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Chen L, He J. Outlier Profiles of Atomic Structures Derived from X-ray Crystallography and from Cryo-Electron Microscopy. Molecules 2020; 25:E1540. [PMID: 32231015 PMCID: PMC7181022 DOI: 10.3390/molecules25071540] [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: 01/23/2020] [Revised: 03/16/2020] [Accepted: 03/24/2020] [Indexed: 11/19/2022] Open
Abstract
Background: As more protein atomic structures are determined from cryo-electron microscopy (cryo-EM) density maps, validation of such structures is an important task. Methods: We applied a histogram-based outlier score (HBOS) to six sets of cryo-EM atomic structures and five sets of X-ray atomic structures, including one derived from X-ray data with better than 1.5 Å resolution. Cryo-EM data sets contain structures released by December 2016 and those released between 2017 and 2019, derived from resolution ranges 0-4 Å and 4-6 Å respectively. Results: The distribution of HBOS values in five sets of X-ray structures show that HBOS is sensitive distinguishing sets of X-ray structures derived from different resolution ranges-higher than 1.5 Å, 1.5-2.0 Å, 2.0-2.5 Å, 2.5-3.0 Å, and 3.0-3.5 Å. The overall quality of cryo-EM structures is likely improved, as shown in a comparison of cryo-EM structures released before the end of 2016, those between 2017 and 2018, and those between 2018 and 2019. Our investigation shows that leucine (LEU) has a significantly higher rate of HBOS outliers than that of the reference data set (X-ray-1.5) and of other residue types in the cryo-EM data sets. HBOS was able to detect outliers for those residues that are currently marked as green in PDB validation reports. Conclusions: The HBOS profile of a dataset is a potential method to characterize the overall structural quality of the set. Residue LEU deserves special attention since it has a significantly higher HBOS outlier rate in sets of cryo-EM structures and those X-ray structures derived from X-ray data of lower than 2.5 Å resolutions. Most HBOS outlier residues from the EM-0-4-2019 set are located on loops for most types of residues.
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Affiliation(s)
- Lin Chen
- Department of Computer Science, Valdosta State University, 1500 N Patterson St, Valdosta, GA 31698, USA
| | - Jing He
- Department of Computer Science, Old Dominion University, 5115 Hampton Blvd, Norfolk, VA 23529, USA;
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55
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Rodríguez CF, Pal M, Muñoz-Hernandez H, Pearl LH, Llorca O. Modeling of a 14 kDa RUVBL2-Binding Domain with Medium Resolution Cryo-EM Density. J Chem Inf Model 2020; 60:2541-2551. [PMID: 32175735 DOI: 10.1021/acs.jcim.9b01095] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The number of high-resolution structures of protein complexes obtained using cryo-electron microscopy (cryo-EM) is increasing rapidly. Cryo-EM maps of large macromolecular complexes frequently contain regions resolved at different resolution levels, and modeling atomic structures de novo can be difficult for domains determined at worse than 5 Å in the absence of atomic information from other structures. Here we describe the details and step-by-step decisions in the strategy we followed to model the RUVBL2-binding domain (RBD), a 14 kDa domain at the C-terminus of RNA Polymerase II associated protein 3 (RPAP3) for which atomic information was not available. Modeling was performed on a cryo-EM map at 4.0-5.5 Å resolution, integrating information from secondary structure predictions, homology modeling, restraints from cross-linked mass spectrometry, and molecular dynamics (MD) in AMBER. Here, we compare our model with the structure of RBD determined by NMR to evaluate our strategy. We also perform new MD simulations to describe important residues mediating the interaction of RBD with RUVBL2 and analyze their conservation in RBD homologous domains. Our approach and its evaluation can serve as an example to address the analysis of medium resolution regions in cryo-EM maps.
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Affiliation(s)
- Carlos F Rodríguez
- Structural Biology Programme, Spanish National Cancer Research Centre (CNIO), Melchor Fernández Almagro 3, 28029 Madrid, Spain
| | - Mohinder Pal
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9RH, U.K
| | - Hugo Muñoz-Hernandez
- Structural Biology Programme, Spanish National Cancer Research Centre (CNIO), Melchor Fernández Almagro 3, 28029 Madrid, Spain
| | - Laurence H Pearl
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9RH, U.K
| | - Oscar Llorca
- Structural Biology Programme, Spanish National Cancer Research Centre (CNIO), Melchor Fernández Almagro 3, 28029 Madrid, Spain
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56
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Si D, Moritz SA, Pfab J, Hou J, Cao R, Wang L, Wu T, Cheng J. Deep Learning to Predict Protein Backbone Structure from High-Resolution Cryo-EM Density Maps. Sci Rep 2020; 10:4282. [PMID: 32152330 PMCID: PMC7063051 DOI: 10.1038/s41598-020-60598-y] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 02/10/2020] [Indexed: 11/29/2022] Open
Abstract
Cryo-electron microscopy (cryo-EM) has become a leading technology for determining protein structures. Recent advances in this field have allowed for atomic resolution. However, predicting the backbone trace of a protein has remained a challenge on all but the most pristine density maps (<2.5 Å resolution). Here we introduce a deep learning model that uses a set of cascaded convolutional neural networks (CNNs) to predict Cα atoms along a protein's backbone structure. The cascaded-CNN (C-CNN) is a novel deep learning architecture comprised of multiple CNNs, each predicting a specific aspect of a protein's structure. This model predicts secondary structure elements (SSEs), backbone structure, and Cα atoms, combining the results of each to produce a complete prediction map. The cascaded-CNN is a semantic segmentation image classifier and was trained using thousands of simulated density maps. This method is largely automatic and only requires a recommended threshold value for each protein density map. A specialized tabu-search path walking algorithm was used to produce an initial backbone trace with Cα placements. A helix-refinement algorithm made further improvements to the α-helix SSEs of the backbone trace. Finally, a novel quality assessment-based combinatorial algorithm was used to effectively map protein sequences onto Cα traces to obtain full-atom protein structures. This method was tested on 50 experimental maps between 2.6 Å and 4.4 Å resolution. It outperformed several state-of-the-art prediction methods including Rosetta de-novo, MAINMAST, and a Phenix based method by producing the most complete predicted protein structures, as measured by percentage of found Cα atoms. This method accurately predicted 88.9% (mean) of the Cα atoms within 3 Å of a protein's backbone structure surpassing the 66.8% mark achieved by the leading alternate method (Phenix based fully automatic method) on the same set of density maps. The C-CNN also achieved an average root-mean-square deviation (RMSD) of 1.24 Å on a set of 50 experimental density maps which was tested by the Phenix based fully automatic method. The source code and demo of this research has been published at https://github.com/DrDongSi/Ca-Backbone-Prediction.
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Affiliation(s)
- Dong Si
- Division of Computing & Software Systems, University of Washington, Bothell, WA, 98011, USA.
| | - Spencer A Moritz
- Division of Computing & Software Systems, University of Washington, Bothell, WA, 98011, USA
| | - Jonas Pfab
- Division of Computing & Software Systems, University of Washington, Bothell, WA, 98011, USA
| | - Jie Hou
- Department of Computer Science, Saint Louis University, Saint Louis, MO, 63103, USA
- Program in Bioinformatics & Computational Biology, Saint Louis University, Saint Louis, MO, 63103, USA
| | - Renzhi Cao
- Department of Computer Science, Pacific Lutheran University, Tacoma, WA, 98447, USA
| | - Liguo Wang
- Department of Biological Structure, University of Washington, Seattle, WA, 98185, USA
| | - Tianqi Wu
- Department of Electrical Engineering and Computer Science, University of Missouri, Columbia, MO, 65211, USA
| | - Jianlin Cheng
- Department of Electrical Engineering and Computer Science, University of Missouri, Columbia, MO, 65211, USA
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57
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Bendory T, Bartesaghi A, Singer A. Single-particle cryo-electron microscopy: Mathematical theory, computational challenges, and opportunities. IEEE SIGNAL PROCESSING MAGAZINE 2020; 37:58-76. [PMID: 32395065 PMCID: PMC7213211 DOI: 10.1109/msp.2019.2957822] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
In recent years, an abundance of new molecular structures have been elucidated using cryo-electron microscopy (cryo-EM), largely due to advances in hardware technology and data processing techniques. Owing to these new exciting developments, cryo-EM was selected by Nature Methods as Method of the Year 2015, and the Nobel Prize in Chemistry 2017 was awarded to three pioneers in the field. The main goal of this article is to introduce the challenging and exciting computational tasks involved in reconstructing 3-D molecular structures by cryo-EM. Determining molecular structures requires a wide range of computational tools in a variety of fields, including signal processing, estimation and detection theory, high-dimensional statistics, convex and non-convex optimization, spectral algorithms, dimensionality reduction, and machine learning. The tools from these fields must be adapted to work under exceptionally challenging conditions, including extreme noise levels, the presence of missing data, and massively large datasets as large as several Terabytes. In addition, we present two statistical models: multi-reference alignment and multi-target detection, that abstract away much of the intricacies of cryo-EM, while retaining some of its essential features. Based on these abstractions, we discuss some recent intriguing results in the mathematical theory of cryo-EM, and delineate relations with group theory, invariant theory, and information theory.
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Affiliation(s)
- Tamir Bendory
- Tel Aviv University, Electrical Engineering, Tel Aviv, Israel
| | - Alberto Bartesaghi
- Computer Science, Biochemistry, and Electrical and Computer Engineering, Durham, NC, USA, Duke University
| | - Amit Singer
- Princeton University, Applied and Computational Mathematics, Princeton, NJ USA
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58
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Saur M, Hartshorn MJ, Dong J, Reeks J, Bunkoczi G, Jhoti H, Williams PA. Fragment-based drug discovery using cryo-EM. Drug Discov Today 2020; 25:485-490. [PMID: 31877353 DOI: 10.1016/j.drudis.2019.12.006] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Revised: 12/12/2019] [Accepted: 12/17/2019] [Indexed: 12/18/2022]
Abstract
Recent advances in electron cryo-microscopy (cryo-EM) structure determination have pushed the resolutions obtainable by the method into the range widely considered to be of utility for drug discovery. Here, we review the use of cryo-EM in fragment-based drug discovery (FBDD) based on in-house method development. We demonstrate not only that cryo-EM can reveal details of the molecular interactions between fragments and a protein, but also that the current reproducibility, quality, and throughput are compatible with FBDD. We exemplify this using the test system β-galactosidase (Bgal) and the oncology target pyruvate kinase 2 (PKM2).
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Affiliation(s)
- Michael Saur
- Astex Pharmaceuticals, 436 Cambridge Science Park, Cambridge, CB4 0QA, UK
| | - Michael J Hartshorn
- Isohelio Ltd, Lewis House, Great Chesterford Court, Great Chesterford, CB10 1PF, UK
| | - Jing Dong
- Astex Pharmaceuticals, 436 Cambridge Science Park, Cambridge, CB4 0QA, UK
| | - Judith Reeks
- Astex Pharmaceuticals, 436 Cambridge Science Park, Cambridge, CB4 0QA, UK
| | - Gabor Bunkoczi
- Astex Pharmaceuticals, 436 Cambridge Science Park, Cambridge, CB4 0QA, UK
| | - Harren Jhoti
- Astex Pharmaceuticals, 436 Cambridge Science Park, Cambridge, CB4 0QA, UK.
| | - Pamela A Williams
- Astex Pharmaceuticals, 436 Cambridge Science Park, Cambridge, CB4 0QA, UK
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59
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Wu M, Lander GC, Herzik MA. Sub-2 Angstrom resolution structure determination using single-particle cryo-EM at 200 keV. J Struct Biol X 2020; 4:100020. [PMID: 32647824 PMCID: PMC7337053 DOI: 10.1016/j.yjsbx.2020.100020] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 02/25/2020] [Accepted: 02/27/2020] [Indexed: 11/30/2022] Open
Abstract
Although the advent of direct electron detectors (DEDs) and software developments have enabled the routine use of single-particle cryogenic electron microscopy (cryo-EM) for structure determination of well-behaved specimens to high-resolution, there nonetheless remains a discrepancy between the resolutions attained for biological specimens and the information limits of modern transmission electron microscopes (TEMs). Instruments operating at 300 kV equipped with DEDs are the current paradigm for high-resolution single-particle cryo-EM, while 200 kV TEMs remain comparatively underutilized for purposes beyond sample screening. Here, we expand upon our prior work and demonstrate that one such 200 kV microscope, the Talos Arctica, equipped with a K2 DED is capable of determining structures of macromolecules to as high as ∼1.7 Å resolution. At this resolution, ordered water molecules are readily assigned and holes in aromatic residues can be clearly distinguished in the reconstructions. This work emphasizes the utility of 200 kV electrons for high-resolution single-particle cryo-EM and applications such as structure-based drug design.
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Affiliation(s)
- Mengyu Wu
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Gabriel C. Lander
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Mark A. Herzik
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, United States
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60
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Tiwari SP, Chhabra S, Tama F, Miyashita O. Computational Protocol for Assessing the Optimal Pixel Size to Improve the Accuracy of Single-particle Cryo-electron Microscopy Maps. J Chem Inf Model 2020; 60:2570-2580. [PMID: 32003995 DOI: 10.1021/acs.jcim.9b01107] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Cryo-electron microscopy (cryo-EM) single-particle analysis has come a long way in achieving atomic-level resolution when imaging biomolecules. To obtain the best possible three-dimensional (3D) structure in cryo-EM, many parameters have to be carefully considered. Here we address the often-overlooked parameter of the pixel size, which describes the magnification of the image produced by the experiment. While efforts are made to refine and validate this parameter in the analysis of cryo-EM experimental data, there is no systematic protocol in place. Since the pixel size parameter can have an impact on the resolution and accuracy of a cryo-EM map, and the atomic resolution 3D structure models derived from it, we propose a computational protocol to estimate the appropriate pixel size parameter. In our protocol, we fit and refine atomic structures against cryo-EM maps at multiple pixel sizes. The resulting fitted and refined structures are evaluated using the GOAP (generalized orientation-dependent, all-atom statistical potential) score, which we found to perform better than other commonly used functions, such as Molprobity and the correlation coefficient from refinement. Finally, we describe the efficacy of this protocol in retrieving appropriate pixel sizes for several examples; simulated data based on yeast elongation factor 2 and experimental data from Gro-EL chaperone, beta-galactosidase, and the TRPV1 ion channel.
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Affiliation(s)
- Sandhya P Tiwari
- Computational Structural Biology Division, RIKEN Center for Computational Science, Kobe, Hyogo Prefecture 650-0047, Japan
| | - Sahil Chhabra
- Department of Chemistry, University of Michigan-Ann Arbor, Ann Arbor, Michigan 48109-1382, United States.,Michigan Institute for Computational Discovery and Engineering, University of Michigan-Ann Arbor, Ann Arbor, Michigan 48109-1382, United States
| | - Florence Tama
- Computational Structural Biology Division, RIKEN Center for Computational Science, Kobe, Hyogo Prefecture 650-0047, Japan.,Graduate School of Science, Department of Physics, Nagoya University, Nagoya, Aichi Prefecture 464-8601, Japan.,Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, Aichi Prefecture 464-8601, Japan
| | - Osamu Miyashita
- Computational Structural Biology Division, RIKEN Center for Computational Science, Kobe, Hyogo Prefecture 650-0047, Japan
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61
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Shigematsu H. Electron cryo-microscopy for elucidating the dynamic nature of live-protein complexes. Biochim Biophys Acta Gen Subj 2020; 1864:129436. [DOI: 10.1016/j.bbagen.2019.129436] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2019] [Revised: 08/31/2019] [Accepted: 09/11/2019] [Indexed: 12/30/2022]
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62
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Song K, Shang Z, Fu X, Lou X, Grigorieff N, Nicastro D. In situ structure determination at nanometer resolution using TYGRESS. Nat Methods 2020; 17:201-208. [PMID: 31768058 PMCID: PMC7004880 DOI: 10.1038/s41592-019-0651-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 09/20/2019] [Accepted: 10/11/2019] [Indexed: 02/06/2023]
Abstract
The resolution of subtomogram averages calculated from cryo-electron tomograms (cryo-ET) of crowded cellular environments is often limited owing to signal loss in, and misalignment of, the subtomograms. By contrast, single-particle cryo-electron microscopy (SP-cryo-EM) routinely reaches near-atomic resolution of isolated complexes. We report a method called 'tomography-guided 3D reconstruction of subcellular structures' (TYGRESS) that is a hybrid of cryo-ET and SP-cryo-EM, and is able to achieve close-to-nanometer resolution of complexes inside crowded cellular environments. TYGRESS combines the advantages of SP-cryo-EM (images with good signal-to-noise ratio and contrast, as well as minimal radiation damage) and subtomogram averaging (three-dimensional alignment of macromolecules in a complex sample). Using TYGRESS, we determined the structure of the intact ciliary axoneme with up to resolution of 12 Å. These results reveal many structural details that were not visible by cryo-ET alone. TYGRESS is generally applicable to cellular complexes that are amenable to subtomogram averaging.
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Affiliation(s)
- Kangkang Song
- Departments of Cell Biology and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Cryo-EM Core Facility, University of Massachusetts Medical School, Worcester, MA, USA
| | - Zhiguo Shang
- Departments of Cell Biology and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Xiaofeng Fu
- Departments of Cell Biology and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Biological Science Imaging Resource, Florida State University, Tallahassee, FL, USA
| | - Xiaochu Lou
- Departments of Cell Biology and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Nikolaus Grigorieff
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Daniela Nicastro
- Departments of Cell Biology and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
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63
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Moscovich A, Halevi A, Andén J, Singer A. Cryo-EM reconstruction of continuous heterogeneity by Laplacian spectral volumes. INVERSE PROBLEMS 2020; 36:024003. [PMID: 32394996 PMCID: PMC7213598 DOI: 10.1088/1361-6420/ab4f55] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Single-particle electron cryomicroscopy is an essential tool for high-resolution 3D reconstruction of proteins and other biological macromolecules. An important challenge in cryo-EM is the reconstruction of non-rigid molecules with parts that move and deform. Traditional reconstruction methods fail in these cases, resulting in smeared reconstructions of the moving parts. This poses a major obstacle for structural biologists, who need high-resolution reconstructions of entire macromolecules, moving parts included. To address this challenge, we present a new method for the reconstruction of macromolecules exhibiting continuous heterogeneity. The proposed method uses projection images from multiple viewing directions to construct a graph Laplacian through which the manifold of three-dimensional conformations is analyzed. The 3D molecular structures are then expanded in a basis of Laplacian eigenvectors, using a novel generalized tomographic reconstruction algorithm to compute the expansion coefficients. These coefficients, which we name spectral volumes, provide a high-resolution visualization of the molecular dynamics. We provide a theoretical analysis and evaluate the method empirically on several simulated data sets.
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Affiliation(s)
- Amit Moscovich
- Program in Applied & Computational Mathematics, Princeton University, Princeton, NJ
| | - Amit Halevi
- Program in Applied & Computational Mathematics, Princeton University, Princeton, NJ
| | - Joakim Andén
- Center for Computational Mathematics, Flatiron Institute, New York, NY
| | - Amit Singer
- Program in Applied & Computational Mathematics, Princeton University, Princeton, NJ
- Department of Mathematics, Princeton University, Princeton, NJ
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64
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Henderson R, Lu M, Zhou Y, Mu Z, Parks R, Han Q, Hsu AL, Carter E, Blanchard SC, Edwards RJ, Wiehe K, Saunders KO, Borgnia MJ, Bartesaghi A, Mothes W, Haynes BF, Acharya P, Munir Alam S. Disruption of the HIV-1 Envelope allosteric network blocks CD4-induced rearrangements. Nat Commun 2020; 11:520. [PMID: 31980614 PMCID: PMC6981184 DOI: 10.1038/s41467-019-14196-w] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Accepted: 12/18/2019] [Indexed: 11/24/2022] Open
Abstract
The trimeric HIV-1 Envelope protein (Env) mediates viral-host cell fusion via a network of conformational transitions, with allosteric elements in each protomer orchestrating host receptor-induced exposure of the co-receptor binding site and fusion elements. To understand the molecular details of this allostery, here, we introduce Env mutations aimed to prevent CD4-induced rearrangements in the HIV-1 BG505 Env trimer. Binding analysis and single-molecule Förster Resonance Energy Transfer confirm that these mutations prevent CD4-induced transitions of the HIV-1 Env. Structural analysis by single-particle cryo-electron microscopy performed on the BG505 SOSIP mutant Env proteins shows rearrangements in the gp120 topological layer contacts with gp41. Displacement of a conserved tryptophan (W571) from its typical pocket in these Env mutants renders the Env insensitive to CD4 binding. These results reveal the critical function of W571 as a conformational switch in Env allostery and receptor-mediated viral entry and provide insights on Env conformation that are relevant for vaccine design.
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Affiliation(s)
- Rory Henderson
- Department of Medicine, Duke University School of Medicine, Durham, NC, 27710, USA.
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA.
| | - Maolin Lu
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, 06536, USA
| | - Ye Zhou
- Department of Computer Science, Duke University, Durham, NC, 27708, USA
| | - Zekun Mu
- Department of Immunology, Duke University School of Medicine, Durham, NC, 27710, USA
| | - Robert Parks
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA
| | - Qifeng Han
- Department of Medicine, Duke University School of Medicine, Durham, NC, 27710, USA
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA
| | - Allen L Hsu
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC, 27709, USA
| | - Elizabeth Carter
- Department of Medicine, Duke University School of Medicine, Durham, NC, 27710, USA
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA
| | - Scott C Blanchard
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY, 10021, USA
- St. Jude Children's Research Hospital, Department of Structural Biology, 262 Danny Thomas Place, Memphis, TN, 38105-3678, USA
| | - R J Edwards
- Department of Medicine, Duke University School of Medicine, Durham, NC, 27710, USA
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA
| | - Kevin Wiehe
- Department of Medicine, Duke University School of Medicine, Durham, NC, 27710, USA
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA
| | - Kevin O Saunders
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA
- Department of Surgery, Duke University School of Medicine, Durham, NC, 27710, USA
| | - Mario J Borgnia
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC, 27709, USA
| | - Alberto Bartesaghi
- Department of Computer Science, Duke University, Durham, NC, 27708, USA
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, 27710, USA
- Department of Electrical and Computer Engineering, Duke University, Durham, NC, 27708, USA
| | - Walther Mothes
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, 06536, USA
| | - Barton F Haynes
- Department of Medicine, Duke University School of Medicine, Durham, NC, 27710, USA
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA
- Department of Immunology, Duke University School of Medicine, Durham, NC, 27710, USA
| | - Priyamvada Acharya
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA.
- Department of Surgery, Duke University School of Medicine, Durham, NC, 27710, USA.
| | - S Munir Alam
- Department of Medicine, Duke University School of Medicine, Durham, NC, 27710, USA.
- Duke Human Vaccine Institute, Duke University School of Medicine, Durham, NC, 27710, USA.
- Department of Pathology, Duke University School of Medicine, Durham, NC, 27710, USA.
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65
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Basu K, Green EM, Cheng Y, Craik CS. Why recombinant antibodies - benefits and applications. Curr Opin Biotechnol 2019; 60:153-158. [PMID: 30849700 PMCID: PMC6728236 DOI: 10.1016/j.copbio.2019.01.012] [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: 10/02/2018] [Revised: 12/22/2018] [Accepted: 01/21/2019] [Indexed: 01/07/2023]
Abstract
Antibodies (Abs) are ubiquitous reagents for biological and biochemical research and are rapidly expanding into new therapeutic areas. They are one of the most important probes for determining how proteins function under normal and pathophysiological conditions. Abs are required for the quantification of targets, detection of temporal and spatial patterns of protein expression in cells and tissues, and identification of interacting partners and their biological activities. Their remarkable specificity and unique binding properties can facilitate three-dimensional structure determination using X-ray crystallography and electron cryomicroscopy. While hybridoma technology that involves animal immunization is often productive, many antigen targets do not generate useful Abs. This is particularly true if unique states of the target or critical non-immunogenic target sequences need to be recognized by the Abs. By using the methods of recombinant antibody generation, identification, and engineering, these 'hybridoma-refractory' antigens can be readily targeted. Specific, reproducible, and renewable recombinant Abs are proving to be invaluable reagents in applications ranging from biological discovery to structure determination of challenging macromolecules.
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Affiliation(s)
- Koli Basu
- Department of Pharmaceutical Chemistry, University of California, San Francisco, United States
| | - Evan M Green
- Department of Biochemistry and Biophysics, University of California, San Francisco, United States
| | - Yifan Cheng
- Department of Biochemistry and Biophysics, University of California, San Francisco, United States; Howard Hughes Medical Institute, University of California, San Francisco, United States
| | - Charles S Craik
- Department of Pharmaceutical Chemistry, University of California, San Francisco, United States
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66
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Abstract
Until recently X-ray crystallography has been the standard technique for virus structure determinations. Available X-ray sources have continuously improved over the decades, leading to the realization of X-ray free-electron lasers (XFELs). They provide high-intensity femtosecond X-ray pulses, which allow for new kinds of experiments by making use of the diffraction-before-destruction principle. By overcoming classical dose constraints, they at least in principle allow researchers to perform X-ray virus structure determination for single particles at room temperature. Simultaneously, the availability of XFELs led to the development of the method of serial femtosecond crystallography, where a crystal structure is determined from the measurement of hundreds to thousands of microcrystals. In the case of virus crystallography this method does not require freezing of the crystals and allows researchers to perform experiments under non-equilibrium conditions (e.g., by laser-induced temperature jumps or rapid chemical mixing), which is currently not possible with electron microscopy.
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Affiliation(s)
- A. Meents
- Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, 22607 Hamburg, Germany
| | - M.O. Wiedorn
- Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, 22607 Hamburg, Germany
- Centre for Ultrafast Imaging, University of Hamburg, 22761 Hamburg, Germany
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67
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Non-uniformity of projection distributions attenuates resolution in Cryo-EM. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 150:160-183. [PMID: 31525386 DOI: 10.1016/j.pbiomolbio.2019.09.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 09/02/2019] [Accepted: 09/07/2019] [Indexed: 11/23/2022]
Abstract
Virtually all single-particle cryo-EM experiments currently suffer from specimen adherence to the air-water interface, leading to a non-uniform distribution in the set of projection views. Whereas it is well accepted that uniform projection distributions can lead to high-resolution reconstructions, non-uniform (anisotropic) distributions can negatively affect map quality, elongate structural features, and in some cases, prohibit interpretation altogether. Although some consequences of non-uniform sampling have been described qualitatively, we know little about how sampling quantitatively affects resolution in cryo-EM. Here, we show how inhomogeneity in any projection distribution scheme attenuates the global Fourier Shell Correlation (FSC) in relation to the number of particles and a single geometrical parameter, which we term the sampling compensation factor (SCF). The reciprocal of the SCF is defined as the average over Fourier shells of the reciprocal of the per-particle sampling and normalized to unity for uniform distributions. The SCF therefore ranges from one to zero, with values close to the latter implying large regions of poorly sampled or completely missing data in Fourier space. Using two synthetic test cases, influenza hemagglutinin and human apoferritin, we demonstrate how any amount of sampling inhomogeneity always attenuates the FSC compared to a uniform distribution. We advocate quantitative evaluation of the SCF criterion to approximate the effect of non-uniform sampling on resolution within experimental single-particle cryo-EM reconstructions.
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68
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Affiliation(s)
- Jean-Paul Armache
- Department of Biochemistry and Molecular Biology and the Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802, USA
| | - Yifan Cheng
- Howard Hughes Medical Institute, University of California San Francisco, USA.,Department of Biochemistry and Biophysics, University of California San Francisco, USA
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69
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Marques MA, Purdy MD, Yeager M. CryoEM maps are full of potential. Curr Opin Struct Biol 2019; 58:214-223. [PMID: 31400843 DOI: 10.1016/j.sbi.2019.04.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Revised: 04/19/2019] [Accepted: 04/19/2019] [Indexed: 01/08/2023]
Abstract
Electron microscopy is based on elastic scattering due to Coulomb forces between the incident electrons and the sample; thus, electron scattering is dependent on the charge distribution in the sample. Unlike atomic scattering factors for X-rays, electron scattering factors for some atoms are strongly dependent on scattering angle, and the scattering factor for ionic oxygen is negative at low scattering angle. This phenomenon can result in a significant negative contribution to Coulomb potential maps by oxygen and can result in deviations in the positions of positive map features from atomic centers. An important factor that can also complicate the interpretation of cryoEM maps is the exquisite sensitivity of macromolecules to damage from electron irradiation, especially the carboxylates of acidic amino acids. Ideally, when compared with electron density maps derived by X-ray crystallography, Coulomb potential maps can provide additional details about the electrostatic environment and charge state of atoms. Enhancements in model building, refinement and computational simulation will be required to realize the full potential of EM-derived maps to reveal deeper insight into the electronic structure and functional properties of macromolecular complexes and their interactions with binding partners, ligands, cofactors, and drugs.
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Affiliation(s)
- Mayra A Marques
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA; Programa de Biologia Estrutural, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Ciência e Tecnologia de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Michael D Purdy
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Mark Yeager
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA; Center for Membrane and Cell Physiology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA; Cardiovascular Research Center, University of Virginia School of Medicine, Charlottesville, VA 22908, USA; Department of Medicine, Division of Cardiovascular Medicine, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
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70
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Zhang C, Cantara W, Jeon Y, Musier-Forsyth K, Grigorieff N, Lyumkis D. Analysis of discrete local variability and structural covariance in macromolecular assemblies using Cryo-EM and focused classification. Ultramicroscopy 2019; 203:170-180. [PMID: 30528101 PMCID: PMC6476647 DOI: 10.1016/j.ultramic.2018.11.016] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 11/07/2018] [Accepted: 11/26/2018] [Indexed: 01/30/2023]
Abstract
Single-particle electron cryo-microscopy and computational image classification can be used to analyze structural variability in macromolecules and their assemblies. In some cases, a particle may contain different regions that each display a range of distinct conformations. We have developed strategies, implemented within the Frealign and cisTEM image processing packages, to focus-classify on specific regions of a particle and detect potential covariance. The strategies are based on masking the region of interest using either a 2-D mask applied to reference projections and particle images, or a 3-D mask applied to the 3-D volume. We show that focused classification approaches can be used to study structural covariance, a concept that is likely to gain more importance as datasets grow in size, allowing the distinction of more structural states and smaller differences between states. Finally, we apply the approaches to an experimental dataset containing the HIV-1 Transactivation Response (TAR) element RNA fused into the large bacterial ribosomal subunit to deconvolve structural mobility within localized regions of interest, and to a dataset containing assembly intermediates of the large subunit to measure structural covariance.
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Affiliation(s)
- Cheng Zhang
- Salk Institute for Biological Studies, 10010 N Torrey Pines Rd, La Jolla, CA 92037, USA
| | - William Cantara
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH 43210, USA
| | - Youngmin Jeon
- Salk Institute for Biological Studies, 10010 N Torrey Pines Rd, La Jolla, CA 92037, USA
| | - Karin Musier-Forsyth
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH 43210, USA
| | - Nikolaus Grigorieff
- Janelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA, USA.
| | - Dmitry Lyumkis
- Salk Institute for Biological Studies, 10010 N Torrey Pines Rd, La Jolla, CA 92037, USA.
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71
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Casañal A, Shakeel S, Passmore LA. Interpretation of medium resolution cryoEM maps of multi-protein complexes. Curr Opin Struct Biol 2019; 58:166-174. [PMID: 31362190 PMCID: PMC6863432 DOI: 10.1016/j.sbi.2019.06.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Revised: 06/14/2019] [Accepted: 06/18/2019] [Indexed: 12/20/2022]
Abstract
CryoEM maps at medium (3.5–6 Å) resolution can be challenging to interpret. Integration of multiple methods can inform cryoEM studies. Mass spectrometry and biochemistry facilitate map interpretation and model building.
Electron cryo-microscopy (cryoEM) is used to determine structures of biological molecules, including multi-protein complexes. Maps at better than 3.0 Å resolution are relatively straightforward to interpret since atomic models of proteins and nucleic acids can be built directly. Still, these resolutions are often difficult to achieve, and map quality frequently varies within a structure. This results in data that are challenging to interpret, especially when crystal structures or suitable homology models are not available. Recent advances in mass spectrometry techniques, computational methods and model building tools facilitate subunit/domain fitting into maps, elucidation of protein contacts, and de novo generation of atomic models. Here, we review techniques for map interpretation and provide examples from recent studies of multi-protein complexes.
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Affiliation(s)
- Ana Casañal
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
| | - Shabih Shakeel
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
| | - Lori A Passmore
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
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72
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Garman EF, Weik M. X-ray radiation damage to biological samples: recent progress. JOURNAL OF SYNCHROTRON RADIATION 2019; 26:907-911. [PMID: 31274412 DOI: 10.1107/s1600577519009408] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2019] [Accepted: 06/30/2019] [Indexed: 05/20/2023]
Abstract
With the continuing development of beamlines for macromolecular crystallography (MX) over the last few years providing ever higher X-ray flux densities, it has become even more important to be aware of the effects of radiation damage on the resulting structures. Nine papers in this issue cover a range of aspects related to the physics and chemistry of the manifestations of this damage, as observed in both MX and small-angle X-ray scattering (SAXS) on crystals, solutions and tissue samples. The reports include measurements of the heating caused by X-ray irradiation in ruby microcrystals, low-dose experiments examining damage rates as a function of incident X-ray energy up to 30 keV on a metallo-enzyme using a CdTe detector of high quantum efficiency as well as a theoretical analysis of the gains predicted in diffraction efficiency using these detectors, a SAXS examination of low-dose radiation exposure effects on the dissociation of a protein complex related to human health, theoretical calculations describing radiation chemistry pathways which aim to explain the specific structural damage widely observed in proteins, investigation of radiation-induced damage effects in a DNA crystal, a case study on a metallo-enzyme where structural movements thought to be mechanism related might actually be radiation-damage-induced changes, and finally a review describing what X-ray radiation-induced cysteine modifications can teach us about protein dynamics and catalysis. These papers, along with some other relevant literature published since the last Journal of Synchrotron Radiation Radiation Damage special issue in 2017, are briefly summarized below.
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Affiliation(s)
- Elspeth F Garman
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Martin Weik
- Univ. Grenoble Alpes, CEA, CNRS, Institut de Biologie Structurale, F-38044 Grenoble, France
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73
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Hamaguchi T, Maki-Yonekura S, Naitow H, Matsuura Y, Ishikawa T, Yonekura K. A new cryo-EM system for single particle analysis. J Struct Biol 2019; 207:40-48. [DOI: 10.1016/j.jsb.2019.04.011] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Revised: 03/16/2019] [Accepted: 04/13/2019] [Indexed: 11/29/2022]
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74
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Fan X, Wang J, Zhang X, Yang Z, Zhang JC, Zhao L, Peng HL, Lei J, Wang HW. Single particle cryo-EM reconstruction of 52 kDa streptavidin at 3.2 Angstrom resolution. Nat Commun 2019; 10:2386. [PMID: 31160591 PMCID: PMC6546690 DOI: 10.1038/s41467-019-10368-w] [Citation(s) in RCA: 91] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Accepted: 05/06/2019] [Indexed: 11/09/2022] Open
Abstract
The fast development of single-particle cryogenic electron microscopy (cryo-EM) has made it more feasible to obtain the 3D structure of well-behaved macromolecules with a molecular weight higher than 300 kDa at ~3 Å resolution. However, it remains a challenge to obtain the high-resolution structures of molecules smaller than 200 kDa using single-particle cryo-EM. In this work, we apply the Cs-corrector-VPP-coupled cryo-EM to study the 52 kDa streptavidin (SA) protein supported on a thin layer of graphene and embedded in vitreous ice. We are able to solve both the apo-SA and biotin-bound SA structures at near-atomic resolution using single-particle cryo-EM. We demonstrate that the method has the potential to determine the structures of molecules as small as 39 kDa. It remains a challenge to obtain high-resolution structures of molecules smaller than 200 kDa using single particle cryo-EM. Here, the authors apply the Cs-corrector-VPP coupled cryo-EM and solve structures of the 52 kDa streptavidin (SA) protein at near-atomic resolution.
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Affiliation(s)
- Xiao Fan
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center of Biological Structures, School of Life Sciences, Tsinghua University, Beijing, 100084, China.,Tsinghua-Peking Joint Center for Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Jia Wang
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center of Biological Structures, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Xing Zhang
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center of Biological Structures, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Zi Yang
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center of Biological Structures, School of Life Sciences, Tsinghua University, Beijing, 100084, China.,Tsinghua-Peking Joint Center for Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Jin-Can Zhang
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, 100871, China
| | - Lingyun Zhao
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center of Biological Structures, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Hai-Lin Peng
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, 100871, China
| | - Jianlin Lei
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center of Biological Structures, School of Life Sciences, Tsinghua University, Beijing, 100084, China. .,Tsinghua-Peking Joint Center for Life Sciences, Tsinghua University, Beijing, 100084, China.
| | - Hong-Wei Wang
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center of Biological Structures, School of Life Sciences, Tsinghua University, Beijing, 100084, China. .,Tsinghua-Peking Joint Center for Life Sciences, Tsinghua University, Beijing, 100084, China.
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75
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García-Nafría J, Tate CG. Cryo-EM structures of GPCRs coupled to G s, G i and G o. Mol Cell Endocrinol 2019; 488:1-13. [PMID: 30930094 DOI: 10.1016/j.mce.2019.02.006] [Citation(s) in RCA: 93] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 02/07/2019] [Accepted: 02/08/2019] [Indexed: 01/14/2023]
Abstract
Advances in electron cryo-microscopy (cryo-EM) now permit the structure determination of G protein-coupled receptors (GPCRs) coupled to heterotrimeric G proteins by single-particle imaging. A combination of G protein engineering and the development of antibodies that stabilise the heterotrimeric G protein facilitate the formation of stable GPCR-G protein complexes suitable for structural biology. Structures have been determined of GPCRs coupled to either heterotrimeric G proteins (Gs, Gi or Go) or mini-G proteins (mini-Gs or mini-Go) by single-particle cryo-EM and X-ray crystallography, respectively. This review describes the technical breakthroughs allowing their structure determination and compares the different techniques. In addition, we compare the structures of GPCRs coupled either to Gs, Gi or Go and analyse the contributions of amino acid residues to the GPCR-G protein interface. There is no unique set of interactions that specifies coupling either to Gs, Gi or Go. Instead, there is a common core of interactions between the C-terminal α-helix of the G protein α-subunit and helices H3, H5 and H6 of the receptor. In addition, there are varying degrees of interaction between all the other GPCR helices and intracellular loops to five regions of the α-subunit and four regions of the β-subunit. These data support the contention that there is not a simple linear barcode that defines the specificity of G protein coupling and thus how a G protein couples to a GPCR cannot currently be determined from simply analysing amino acid sequences. Although the overall architecture of GPCR-G protein complexes is conserved, there are significant differences in the molecular details. The number and type of molecular interactions between amino acid residues at the interfaces varies, resulting in subtly different orientation and position of the G protein with respect to the GPCR. This in turn affects the interface surface area that varies between 845 Å2 and 1490 Å2, which could impact upon the lifetime of signalling complexes in the cell.
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Affiliation(s)
- Javier García-Nafría
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK
| | - Christopher G Tate
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
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76
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Abstract
Cryogenic electron microscopy (cryo-EM) enables structure determination of macromolecular objects and their assemblies. Although the techniques have been developing for nearly four decades, they have gained widespread attention in recent years due to technical advances on numerous fronts, enabling traditional microscopists to break into the world of molecular structural biology. Many samples can now be routinely analyzed at near-atomic resolution using standard imaging and image analysis techniques. However, numerous challenges to conventional workflows remain, and continued technical advances open entirely novel opportunities for discovery and exploration. Here, I will review some of the main methods surrounding cryo-EM with an emphasis specifically on single-particle analysis, and I will highlight challenges, open questions, and opportunities for methodology development.
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Affiliation(s)
- Dmitry Lyumkis
- From the Laboratory of Genetics and Helmsley Center for Genomic Medicine, The Salk Institute for Biological Studies, La Jolla, California 92037
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77
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Chen CY, Chang YC, Lin BL, Lin KF, Huang CH, Hsieh DL, Ko TP, Tsai MD. Use of Cryo-EM To Uncover Structural Bases of pH Effect and Cofactor Bispecificity of Ketol-Acid Reductoisomerase. J Am Chem Soc 2019; 141:6136-6140. [DOI: 10.1021/jacs.9b01354] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Chin-Yu Chen
- Department of Life Sciences, National Central University, Taoyuan 32001, Taiwan
| | | | | | - Kuan-Fu Lin
- Department of Life Sciences, National Central University, Taoyuan 32001, Taiwan
| | - Chun-Hsiang Huang
- Experimental Facility Division, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Dong-Lin Hsieh
- Department of Life Sciences, National Central University, Taoyuan 32001, Taiwan
| | | | - Ming-Daw Tsai
- Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan
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78
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Ognjenović J, Grisshammer R, Subramaniam S. Frontiers in Cryo Electron Microscopy of Complex Macromolecular Assemblies. Annu Rev Biomed Eng 2019; 21:395-415. [PMID: 30892930 DOI: 10.1146/annurev-bioeng-060418-052453] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In recent years, cryo electron microscopy (cryo-EM) technology has been transformed with the development of better instrumentation, direct electron detectors, improved methods for specimen preparation, and improved software for data analysis. Analyses using single-particle cryo-EM methods have enabled determination of structures of proteins with sizes smaller than 100 kDa and resolutions of ∼2 Å in some cases. The use of electron tomography combined with subvolume averaging is beginning to allow the visualization of macromolecular complexes in their native environment in unprecedented detail. As a result of these advances, solutions to many intractable challenges in structural and cell biology, such as analysis of highly dynamic soluble and membrane-embedded protein complexes or partially ordered protein aggregates, are now within reach. Recent reports of structural studies of G protein-coupled receptors, spliceosomes, and fibrillar specimens illustrate the progress that has been made using cryo-EM methods, and are the main focus of this review.
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Affiliation(s)
- Jana Ognjenović
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20814, USA; ,
| | - Reinhard Grisshammer
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20814, USA; ,
| | - Sriram Subramaniam
- University of British Columbia, Vancouver, British Columbia V6T 1Z2, Canada;
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79
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Herzik MA, Wu M, Lander GC. High-resolution structure determination of sub-100 kDa complexes using conventional cryo-EM. Nat Commun 2019; 10:1032. [PMID: 30833564 PMCID: PMC6399227 DOI: 10.1038/s41467-019-08991-8] [Citation(s) in RCA: 131] [Impact Index Per Article: 26.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 02/11/2019] [Indexed: 12/31/2022] Open
Abstract
Determining high-resolution structures of biological macromolecules amassing less than 100 kilodaltons (kDa) has been a longstanding goal of the cryo-electron microscopy (cryo-EM) community. While the Volta phase plate has enabled visualization of specimens in this size range, this instrumentation is not yet fully automated and can present technical challenges. Here, we show that conventional defocus-based cryo-EM methodologies can be used to determine high-resolution structures of specimens amassing less than 100 kDa using a transmission electron microscope operating at 200 keV coupled with a direct electron detector. Our ~2.7 Å structure of alcohol dehydrogenase (82 kDa) proves that bound ligands can be resolved with high fidelity to enable investigation of drug-target interactions. Our ~2.8 Å and ~3.2 Å structures of methemoglobin demonstrate that distinct conformational states can be identified within a dataset for proteins as small as 64 kDa. Furthermore, we provide the sub-nanometer cryo-EM structure of a sub-50 kDa protein.
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Affiliation(s)
- Mark A Herzik
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, 92037, USA
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, 92093, USA
| | - Mengyu Wu
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, 92037, USA
| | - Gabriel C Lander
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, 92037, USA.
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80
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Kumar P, Gruza B, Bojarowski SA, Dominiak PM. Extension of the transferable aspherical pseudoatom data bank for the comparison of molecular electrostatic potentials in structure-activity studies. ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES 2019; 75:398-408. [PMID: 30821272 DOI: 10.1107/s2053273319000482] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Accepted: 01/09/2019] [Indexed: 12/31/2022]
Abstract
The transferable aspherical pseudoatom data bank, UBDB2018, is extended with over 130 new atom types present in small and biological molecules of great importance in biology and chemistry. UBDB2018 can be applied either as a source of aspherical atomic scattering factors in a standard X-ray experiment (dmin ≃ 0.8 Å) instead of the independent atom model (IAM), and can therefore enhance the final crystal structure geometry and refinement parameters; or as a tool to reconstruct the molecular charge-density distribution and derive the electrostatic properties of chemical systems for which 3D structural data are available. The extended data bank has been extensively tested, with the focus being on the accuracy of the molecular electrostatic potential computed for important drug-like molecules, namely the HIV-1 protease inhibitors. The UBDB allows the reconstruction of the reference B3LYP/6-31G** potentials, with a root-mean-squared error of 0.015 e bohr-1 computed for entire potential grids which span values from ca 200 e bohr-1 to ca -0.1 e bohr-1 and encompass both the inside and outside regions of a molecule. UBDB2018 is shown to be applicable to enhancing the physical meaning of the molecular electrostatic potential descriptors used to construct predictive quantitative structure-activity relationship/quantitative structure-property relationship (QSAR/QSPR) models for drug discovery studies. In addition, it is suggested that electron structure factors computed from UBDB2018 may significantly improve the interpretation of electrostatic potential maps measured experimentally by means of electron diffraction or single-particle cryo-EM methods.
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Affiliation(s)
- Prashant Kumar
- Biological and Chemical Research Centre, Department of Chemistry, University of Warsaw, ul. Żwirki i Wigury 101, Warszawa 02-089, Poland
| | - Barbara Gruza
- Biological and Chemical Research Centre, Department of Chemistry, University of Warsaw, ul. Żwirki i Wigury 101, Warszawa 02-089, Poland
| | - Sławomir Antoni Bojarowski
- Biological and Chemical Research Centre, Department of Chemistry, University of Warsaw, ul. Żwirki i Wigury 101, Warszawa 02-089, Poland
| | - Paulina Maria Dominiak
- Biological and Chemical Research Centre, Department of Chemistry, University of Warsaw, ul. Żwirki i Wigury 101, Warszawa 02-089, Poland
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81
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Capabilities of the Falcon III detector for single-particle structure determination. Ultramicroscopy 2019; 203:145-154. [PMID: 30738626 DOI: 10.1016/j.ultramic.2019.01.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Revised: 01/10/2019] [Accepted: 01/26/2019] [Indexed: 02/02/2023]
Abstract
Direct electron detectors are an essential asset for the resolution revolution in electron cryo microscopy of biological objects. The direct detectors provide two modes of data acquisition; the counting mode in which single electrons are counted, and the integrating mode in which the signal that arises from the incident electrons is integrated. While counting mode leads to far higher detective quantum efficiency at all spatial frequencies, the integrating mode enables faster data acquisition at higher exposure rates. For optimal throughput at best possible resolution it is important to understand when the better performance in counting mode becomes essential for solving a structure and when the lower detective quantum efficiency in integrating mode can be compensated by increasing the number of particles in the data set. Here, we provide a case study of the Falcon III camera, which has counting mode capability at exposure rates of <0.9 e-/Px² and integrating mode capability at exposure rates above 10 e-/Px². We found that counting mode gives better resolution for medium sized complexes such as the β-galactosidase (465 kDa) (2.2 Å, 97% of Nyquist vs. 2.4 Å, 89% of Nyquist) with data sets of similar size. However, for larger particles such as Hepatitis B virus capsid like particles (4.8 MDa) we did not find any resolution gain in counting mode.
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82
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Cryo-EM in drug discovery. Biochem Soc Trans 2019; 47:281-293. [PMID: 30647139 DOI: 10.1042/bst20180267] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Revised: 12/05/2018] [Accepted: 12/06/2018] [Indexed: 01/11/2023]
Abstract
The impact of structural biology on drug discovery is well documented, and the workhorse technique for the past 30 years or so has been X-ray crystallography. With the advent of several technological improvements, including direct electron detectors, automation, better microscope vacuums and lenses, phase plates and improvements in computing power enabled by GPUs, it is now possible to record and analyse images of protein structures containing high-resolution information. This review, from a pharmaceutical perspective, highlights some of the most relevant and interesting protein structures for the pharmaceutical industry and shows examples of how ligand-binding sites, membrane proteins, both big and small, pseudo symmetry and complexes are being addressed by this technique.
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83
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Beckers M, Jakobi AJ, Sachse C. Thresholding of cryo-EM density maps by false discovery rate control. IUCRJ 2019; 6:18-33. [PMID: 30713700 PMCID: PMC6327189 DOI: 10.1107/s2052252518014434] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 10/12/2018] [Indexed: 05/31/2023]
Abstract
Cryo-EM now commonly generates close-to-atomic resolution as well as intermediate resolution maps from macromolecules observed in isolation and in situ. Interpreting these maps remains a challenging task owing to poor signal in the highest resolution shells and the necessity to select a threshold for density analysis. In order to facilitate this process, a statistical framework for the generation of confidence maps by multiple hypothesis testing and false discovery rate (FDR) control has been developed. In this way, three-dimensional confidence maps contain signal separated from background noise in the form of local detection rates of EM density values. It is demonstrated that confidence maps and FDR-based thresholding can be used for the interpretation of near-atomic resolution single-particle structures as well as lower resolution maps determined by subtomogram averaging. Confidence maps represent a conservative way of interpreting molecular structures owing to minimized noise. At the same time they provide a detection error with respect to background noise, which is associated with the density and is particularly beneficial for the interpretation of weaker cryo-EM densities in cases of conformational flexibility and lower occupancy of bound molecules and ions in the structure.
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Affiliation(s)
- Maximilian Beckers
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
- Faculty of Biosciences, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Arjen J. Jakobi
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
- Hamburg Unit c/o DESY, Notkestrasse 85, 22607 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging (CUI), Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Carsten Sachse
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C-3/Structural Biology), Forschungszentrum Jülich, 52425 Jülich, Germany
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84
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Little MS, Ervin SM, Walton WG, Tripathy A, Xu Y, Liu J, Redinbo MR. Active site flexibility revealed in crystal structures of Parabacteroides merdae β-glucuronidase from the human gut microbiome. Protein Sci 2018; 27:2010-2022. [PMID: 30230652 PMCID: PMC6237702 DOI: 10.1002/pro.3507] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Revised: 09/10/2018] [Accepted: 09/10/2018] [Indexed: 12/12/2022]
Abstract
β-Glucuronidase (GUS) enzymes in the gastrointestinal tract are involved in maintaining mammalian-microbial symbiosis and can play key roles in drug efficacy and toxicity. Parabacteroides merdae GUS was identified as an abundant mini-Loop 2 (mL2) type GUS enzyme in the Human Microbiome Project gut metagenomic database. Here, we report the crystal structure of P. merdae GUS and highlight the differences between this enzyme and extant structures of gut microbial GUS proteins. We find that P. merdae GUS exhibits a distinct tetrameric quaternary structure and that the mL2 motif traces a unique path within the active site, which also includes two arginines distinctive to this GUS. We observe two states of the P. merdae GUS active site; a loop repositions itself by more than 50 Å to place a functionally-relevant residue into the enzyme's catalytic site. Finally, we find that P. merdae GUS is able to bind to homo and heteropolymers of the polysaccharide alginic acid. Together, these data broaden our understanding of the structural and functional diversity in the GUS family of enzymes present in the human gut microbiome and point to specialization as an important feature of microbial GUS orthologs.
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Affiliation(s)
- Michael S. Little
- Department of ChemistryUniversity of North CarolinaChapel HillNorth Carolina27599‐3290
| | - Samantha M. Ervin
- Department of ChemistryUniversity of North CarolinaChapel HillNorth Carolina27599‐3290
| | - William G. Walton
- Department of ChemistryUniversity of North CarolinaChapel HillNorth Carolina27599‐3290
| | - Ashutosh Tripathy
- Department of Biochemistry & BiophysicsUniversity of North CarolinaChapel HillNorth Carolina27599‐3290
| | - Yongmei Xu
- Department of Chemical Biology and Medicinal ChemistryUniversity of North CarolinaChapel HillNorth Carolina27599‐3290
| | - Jian Liu
- Department of Chemical Biology and Medicinal ChemistryUniversity of North CarolinaChapel HillNorth Carolina27599‐3290
| | - Matthew R. Redinbo
- Department of ChemistryUniversity of North CarolinaChapel HillNorth Carolina27599‐3290
- Department of Biochemistry & BiophysicsUniversity of North CarolinaChapel HillNorth Carolina27599‐3290
- Department of Microbiology & ImmunologyUniversity of North CarolinaChapel HillNorth Carolina27599‐3290
- The Integrated Program for Biological and Genome Sciences, University of North CarolinaChapel HillNorth Carolina27599‐3290
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85
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Zivanov J, Nakane T, Forsberg BO, Kimanius D, Hagen WJ, Lindahl E, Scheres SH. New tools for automated high-resolution cryo-EM structure determination in RELION-3. eLife 2018; 7:42166. [PMID: 30412051 PMCID: PMC6250425 DOI: 10.7554/elife.42166] [Citation(s) in RCA: 3106] [Impact Index Per Article: 517.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2018] [Accepted: 11/06/2018] [Indexed: 12/28/2022] Open
Abstract
Here, we describe the third major release of RELION. CPU-based vector acceleration has been added in addition to GPU support, which provides flexibility in use of resources and avoids memory limitations. Reference-free autopicking with Laplacian-of-Gaussian filtering and execution of jobs from python allows non-interactive processing during acquisition, including 2D-classification, de novo model generation and 3D-classification. Per-particle refinement of CTF parameters and correction of estimated beam tilt provides higher resolution reconstructions when particles are at different heights in the ice, and/or coma-free alignment has not been optimal. Ewald sphere curvature correction improves resolution for large particles. We illustrate these developments with publicly available data sets: together with a Bayesian approach to beam-induced motion correction it leads to resolution improvements of 0.2–0.7 Å compared to previous RELION versions.
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Affiliation(s)
- Jasenko Zivanov
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Takanori Nakane
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Björn O Forsberg
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Dari Kimanius
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Wim Jh Hagen
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Cryo-Electron Microscopy Service Platform, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Erik Lindahl
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden.,Department of Applied Physics, Swedish e-Science Research Center, KTH Royal Institute of Technology, Stockholm, Sweden
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86
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Sub-2 Å Ewald curvature corrected structure of an AAV2 capsid variant. Nat Commun 2018; 9:3628. [PMID: 30194371 PMCID: PMC6128836 DOI: 10.1038/s41467-018-06076-6] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Accepted: 08/11/2018] [Indexed: 01/08/2023] Open
Abstract
Single-particle cryogenic electron microscopy (cryo-EM) provides a powerful methodology for structural biologists, but the resolutions typically attained with experimentally determined structures have lagged behind microscope capabilities. Here, we exploit several technical advances to improve resolution, including per-particle contrast transfer function (CTF) refinement and correction for Ewald sphere curvature. The latter is demonstrated with several experimental samples and should become more standard as resolutions increase or at lower microscope accelerating voltages. The combined application of the described methods to micrographs recorded on a Titan Krios enables structure determination at ~1.86-Å resolution of an adeno-associated virus serotype 2 variant (AAV2), an important gene-delivery vehicle. The resulting structural details provide an improved model for understanding the biology of AAV that will guide future vector development for gene therapy. Single-particle cryo-EM is a powerful method for macromolecular structure determination. Here the authors demonstrate that Ewald sphere curvature correction, sub-Angstrom pixilation and per-particle CTF refinement can improve map quality and resolution and present the 1.86 Å cryo-EM structure of an adeno-associated virus serotype 2 variant.
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87
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Kotev M, Pascual R, Almansa C, Guallar V, Soliva R. Pushing the Limits of Computational Structure-Based Drug Design with a Cryo-EM Structure: The Ca 2+ Channel α2δ-1 Subunit as a Test Case. J Chem Inf Model 2018; 58:1707-1715. [PMID: 30053380 DOI: 10.1021/acs.jcim.8b00347] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cryo-electron microscopy (cryo-EM) is emerging as a real alternative for structural elucidation. In spite of this, very few cryo-EM structures have been described so far as successful platforms for in silico drug design. Gabapentin and pregabalin are some of the most successful drugs in the treatment of epilepsy and neuropathic pain. Although both are in clinical use and are known to exert their effects by binding to the regulatory α2δ subunit of voltage gated calcium channels, their binding modes have never been characterized. We describe here the successful use of an exhaustive protein-ligand sampling algorithm on the α2δ-1 subunit of the recently published cryo-EM structure, with the goal of characterizing the ligand entry path and binding mode for gabapentin, pregabalin, and several other amino acidic α2δ-1 ligands. Our studies indicate that (i) all simulated drugs explore the same path for accessing the occluded binding site on the interior of the α2δ-1 subunit; (ii) they all roughly occupy the same pocket; (iii) the plasticity of the binding site allows the accommodation of a variety of amino acidic modulators, driven by the flexible "capping loop" delineated by residues Tyr426-Val435 and the floppy nature of Arg217; (iv) the predicted binding modes are in line with previously available mutagenesis data, confirming Arg217 as key for binding, with Asp428 and Asp467 highlighted as additional anchoring points for all amino acidic drugs. The study is one of the first proofs that latest-generation cryo-EM structures combined with exhaustive computational methods can be exploited in early drug discovery.
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Affiliation(s)
- Martin Kotev
- Nostrum Biodiscovery , Jordi Girona 29, Nexus II D128 , 08034 Barcelona , Spain
| | - Rosalia Pascual
- Esteve Pharmaceuticals S.A., Drug Discovery and Preclinical Development , Carrer Baldiri Reixac, 4-8. Parc Científic de Barcelona , 08028 Barcelona , Spain
| | - Carmen Almansa
- Esteve Pharmaceuticals S.A., Drug Discovery and Preclinical Development , Carrer Baldiri Reixac, 4-8. Parc Científic de Barcelona , 08028 Barcelona , Spain
| | - Victor Guallar
- Barcelona Supercomputing Center (BSC) , Jordi Girona 29 , E-08034 Barcelona , Spain.,ICREA , Passeig Lluís Companys 23 , E-08010 Barcelona , Spain
| | - Robert Soliva
- Nostrum Biodiscovery , Jordi Girona 29, Nexus II D128 , 08034 Barcelona , Spain
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88
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The first single particle analysis Map Challenge: A summary of the assessments. J Struct Biol 2018; 204:291-300. [PMID: 30114512 DOI: 10.1016/j.jsb.2018.08.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Revised: 08/03/2018] [Accepted: 08/11/2018] [Indexed: 12/13/2022]
Abstract
The recent successes of cryo-electron microscopy fostered great expectation of solving many new and previously recalcitrant biomolecular structures. However, it also brings with it the danger of compromising the validity of the outcomes if not done properly. The Map Challenge is a first step in assessing the state of the art and to shape future developments in data processing. The organizers presented seven cases for single particle reconstruction, and 27 members of the community responded with 66 submissions. Seven groups analyzed these submissions, resulting in several assessment reports, summarized here. We devised a range of analyses to evaluate the submitted maps, including visual impressions, Fourier shell correlation, pairwise similarity and interpretation through modeling. Unfortunately, we did not find strong trends. We ascribe this to the complexity of the challenge, dealing with multiple cases, software packages and processing approaches. This puts the user in the spotlight, where his/her choices becomes the determinant of map quality. The future focus should therefore be on promulgating best practices and encapsulating these in the software. Such practices include adherence to validation principles, most notably the processing of independent sets, proper resolution-limited alignment, appropriate masking and map sharpening. We consider the Map Challenge to be a highly valuable exercise that should be repeated frequently or on an ongoing basis.
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