1
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Sprankel L, Scheffer MP, Manger S, Ermel UH, Frangakis AS. Cryo-electron tomography reveals the binding and release states of the major adhesion complex from Mycoplasma genitalium. PLoS Pathog 2023; 19:e1011761. [PMID: 37939157 PMCID: PMC10659161 DOI: 10.1371/journal.ppat.1011761] [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: 06/20/2023] [Revised: 11/20/2023] [Accepted: 10/17/2023] [Indexed: 11/10/2023] Open
Abstract
The nap particle is an immunogenic surface adhesion complex from Mycoplasma genitalium. It is essential for motility and responsible for binding sialylated oligosaccharides on the surface of the host cell. The nap particle is composed of two P140-P110 heterodimers, the structure of which was recently solved. However, the interpretation of the mechanism by which the mycoplasma cells orchestrate adhesion remained challenging. Here, we provide cryo-electron tomography structures at ~11 Å resolution, which allow for the distinction between the bound and released state of the nap particle, displaying the in vivo conformational states. Fitting of the atomically resolved structures reveals that bound sialylated oligosaccharides are stabilized by both P110 and P140. Movement of the stalk domains allows for the transfer of conformational changes from the interior of the cell to the binding pocket, thus having the capability of an active release process. It is likely that the same mechanism can be transferred to other Mycoplasma species that belong to the pneumoniae cluster.
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Affiliation(s)
- Lasse Sprankel
- Buchmann Institute for Molecular Life Sciences and Institute of Biophysics, Goethe University Frankfurt, Frankfurt, Germany
| | - Margot P. Scheffer
- Buchmann Institute for Molecular Life Sciences and Institute of Biophysics, Goethe University Frankfurt, Frankfurt, Germany
| | - Sina Manger
- Buchmann Institute for Molecular Life Sciences and Institute of Biophysics, Goethe University Frankfurt, Frankfurt, Germany
| | - Utz H. Ermel
- Buchmann Institute for Molecular Life Sciences and Institute of Biophysics, Goethe University Frankfurt, Frankfurt, Germany
| | - Achilleas S. Frangakis
- Buchmann Institute for Molecular Life Sciences and Institute of Biophysics, Goethe University Frankfurt, Frankfurt, Germany
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2
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Kim HHS, Uddin MR, Xu M, Chang YW. Computational Methods Toward Unbiased Pattern Mining and Structure Determination in Cryo-Electron Tomography Data. J Mol Biol 2023; 435:168068. [PMID: 37003470 PMCID: PMC10164694 DOI: 10.1016/j.jmb.2023.168068] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 02/19/2023] [Accepted: 03/26/2023] [Indexed: 04/03/2023]
Abstract
Cryo-electron tomography can uniquely probe the native cellular environment for macromolecular structures. Tomograms feature complex data with densities of diverse, densely crowded macromolecular complexes, low signal-to-noise, and artifacts such as the missing wedge effect. Post-processing of this data generally involves isolating regions or particles of interest from tomograms, organizing them into related groups, and rendering final structures through subtomogram averaging. Template-matching and reference-based structure determination are popular analysis methods but are vulnerable to biases and can often require significant user input. Most importantly, these approaches cannot identify novel complexes that reside within the imaged cellular environment. To reliably extract and resolve structures of interest, efficient and unbiased approaches are therefore of great value. This review highlights notable computational software and discusses how they contribute to making automated structural pattern discovery a possibility. Perspectives emphasizing the importance of features for user-friendliness and accessibility are also presented.
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Affiliation(s)
- Hannah Hyun-Sook Kim
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA. https://twitter.com/hannahinthelab
| | - Mostofa Rafid Uddin
- Computational Biology Department, School of Computer Science, Carnegie Mellon University, Pittsburgh, PA, USA. https://twitter.com/duran_rafid
| | - Min Xu
- Computational Biology Department, School of Computer Science, Carnegie Mellon University, Pittsburgh, PA, USA.
| | - Yi-Wei Chang
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
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3
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Otsuka S, Tempkin JOB, Zhang W, Politi AZ, Rybina A, Hossain MJ, Kueblbeck M, Callegari A, Koch B, Morero NR, Sali A, Ellenberg J. A quantitative map of nuclear pore assembly reveals two distinct mechanisms. Nature 2023; 613:575-581. [PMID: 36599981 PMCID: PMC9849139 DOI: 10.1038/s41586-022-05528-w] [Citation(s) in RCA: 24] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Accepted: 11/04/2022] [Indexed: 01/05/2023]
Abstract
Understanding how the nuclear pore complex (NPC) is assembled is of fundamental importance to grasp the mechanisms behind its essential function and understand its role during the evolution of eukaryotes1-4. There are at least two NPC assembly pathways-one during the exit from mitosis and one during nuclear growth in interphase-but we currently lack a quantitative map of these events. Here we use fluorescence correlation spectroscopy calibrated live imaging of endogenously fluorescently tagged nucleoporins to map the changes in the composition and stoichiometry of seven major modules of the human NPC during its assembly in single dividing cells. This systematic quantitative map reveals that the two assembly pathways have distinct molecular mechanisms, in which the order of addition of two large structural components, the central ring complex and nuclear filaments are inverted. The dynamic stoichiometry data was integrated to create a spatiotemporal model of the NPC assembly pathway and predict the structures of postmitotic NPC assembly intermediates.
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Affiliation(s)
- Shotaro Otsuka
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
- Max Perutz Labs, University of Vienna and the Medical University of Vienna, Vienna Biocenter (VBC), Vienna, Austria.
| | - Jeremy O B Tempkin
- Department of Bioengineering and Therapeutic Sciences, Department of Pharmaceutical Chemistry, Quantitative Biosciences Institute, University of California, San Francisco, San Francisco, CA, USA
| | - Wanlu Zhang
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Antonio Z Politi
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
- Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Arina Rybina
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - M Julius Hossain
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
- Centre for Cancer Immunology, Faculty of Medicine, University of Southampton, Southampton, UK
| | - Moritz Kueblbeck
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Andrea Callegari
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Birgit Koch
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
- Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Natalia Rosalia Morero
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Andrej Sali
- Department of Bioengineering and Therapeutic Sciences, Department of Pharmaceutical Chemistry, Quantitative Biosciences Institute, University of California, San Francisco, San Francisco, CA, USA
| | - Jan Ellenberg
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
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4
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In silico reconstitution of DNA replication. Lessons from single-molecule imaging and cryo-tomography applied to single-particle cryo-EM. Curr Opin Struct Biol 2022; 72:279-286. [PMID: 35026552 PMCID: PMC8869182 DOI: 10.1016/j.sbi.2021.11.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 11/11/2021] [Accepted: 11/28/2021] [Indexed: 11/26/2022]
Abstract
DNA replication has been reconstituted in vitro with yeast proteins, and the minimal system requires the coordinated assembly of 16 distinct replication factors, consisting of 42 polypeptides. To understand the molecular interplay between these factors at the single residue level, new structural biology tools are being developed. Inspired by advances in single-molecule fluorescence imaging and cryo-tomography, novel single-particle cryo-EM experiments have been used to characterise the structural mechanism for the loading of the replicative helicase. Here, we discuss how in silico reconstitution of single-particle cryo-EM data can help describe dynamic systems that are difficult to approach with conventional three-dimensional classification tools.
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5
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Frangakis AS. It's noisy out there! A review of denoising techniques in cryo-electron tomography. J Struct Biol 2021; 213:107804. [PMID: 34732363 DOI: 10.1016/j.jsb.2021.107804] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Revised: 10/14/2021] [Accepted: 10/19/2021] [Indexed: 11/16/2022]
Abstract
Cryo-electron tomography is the only technique that can provide sub-nanometer resolved images of cell regions or even whole cells, without the need of labeling or staining methods. Technological advances over the past decade in electron microscope stability, cameras, stage precision and software have resulted in faster acquisition speeds and considerably improved resolution. In pursuit of even better image resolution, researchers seek to reduce noise - a crucial factor affecting the reliability of the tomogram interpretation and ultimately limiting the achieved resolution. Sub-tomogram averaging is the method of choice for reducing noise in repetitive objects. However, when averaging is not applicable, a trade-off between reducing noise and conserving genuine image details must be achieved. Thus, denoising is an important process that improves the interpretability of the tomogram not only directly but also by facilitating other downstream tasks, such as segmentation and 3D visualization. Here, I review contemporary denoising techniques for cryo-electron tomography by taking into account noise-specific properties of both reconstruction and detector noise. The outcomes of different techniques are compared, in order to help researchers select the most appropriate for each dataset and to achieve better and more reliable interpretation of the tomograms.
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Affiliation(s)
- Achilleas S Frangakis
- Buchmann Institute for Molecular Life Sciences and Institute for Biophysics, Goethe University Frankfurt Max-von-Laue-Str. 15, Frankfurt am Main, D-60438, Germany.
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6
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Garriga D, Chichón FJ, Calisto BM, Ferrero DS, Gastaminza P, Pereiro E, Pérez-Berna AJ. Imaging of Virus-Infected Cells with Soft X-ray Tomography. Viruses 2021; 13:v13112109. [PMID: 34834916 PMCID: PMC8618346 DOI: 10.3390/v13112109] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Revised: 10/13/2021] [Accepted: 10/14/2021] [Indexed: 02/07/2023] Open
Abstract
Viruses are obligate parasites that depend on a host cell for replication and survival. Consequently, to fully understand the viral processes involved in infection and replication, it is fundamental to study them in the cellular context. Often, viral infections induce significant changes in the subcellular organization of the host cell due to the formation of viral factories, alteration of cell cytoskeleton and/or budding of newly formed particles. Accurate 3D mapping of organelle reorganization in infected cells can thus provide valuable information for both basic virus research and antiviral drug development. Among the available techniques for 3D cell imaging, cryo-soft X-ray tomography stands out for its large depth of view (allowing for 10 µm thick biological samples to be imaged without further thinning), its resolution (about 50 nm for tomographies, sufficient to detect viral particles), the minimal requirements for sample manipulation (can be used on frozen, unfixed and unstained whole cells) and the potential to be combined with other techniques (i.e., correlative fluorescence microscopy). In this review we describe the fundamentals of cryo-soft X-ray tomography, its sample requirements, its advantages and its limitations. To highlight the potential of this technique, examples of virus research performed at BL09-MISTRAL beamline in ALBA synchrotron are also presented.
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Affiliation(s)
- Damià Garriga
- ALBA Synchrotron Light Source, 08290 Cerdanyola del Vallès, Spain; (D.G.); (B.M.C.); (E.P.)
| | - Francisco Javier Chichón
- Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain; (F.J.C.); (P.G.)
| | - Bárbara M. Calisto
- ALBA Synchrotron Light Source, 08290 Cerdanyola del Vallès, Spain; (D.G.); (B.M.C.); (E.P.)
| | - Diego S. Ferrero
- Institut de Biologia Molecular de Barcelona, Consejo Superior de Investigaciones Científicas, Parc Científic de Barcelona, 08028 Barcelona, Spain;
| | - Pablo Gastaminza
- Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain; (F.J.C.); (P.G.)
| | - Eva Pereiro
- ALBA Synchrotron Light Source, 08290 Cerdanyola del Vallès, Spain; (D.G.); (B.M.C.); (E.P.)
| | - Ana Joaquina Pérez-Berna
- ALBA Synchrotron Light Source, 08290 Cerdanyola del Vallès, Spain; (D.G.); (B.M.C.); (E.P.)
- Correspondence: ; Tel.: +34-93-592-4371
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7
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Turk M, Baumeister W. The promise and the challenges of cryo-electron tomography. FEBS Lett 2020; 594:3243-3261. [PMID: 33020915 DOI: 10.1002/1873-3468.13948] [Citation(s) in RCA: 137] [Impact Index Per Article: 34.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 09/28/2020] [Accepted: 09/28/2020] [Indexed: 01/11/2023]
Abstract
Structural biologists have traditionally approached cellular complexity in a reductionist manner in which the cellular molecular components are fractionated and purified before being studied individually. This 'divide and conquer' approach has been highly successful. However, awareness has grown in recent years that biological functions can rarely be attributed to individual macromolecules. Most cellular functions arise from their concerted action, and there is thus a need for methods enabling structural studies performed in situ, ideally in unperturbed cellular environments. Cryo-electron tomography (Cryo-ET) combines the power of 3D molecular-level imaging with the best structural preservation that is physically possible to achieve. Thus, it has a unique potential to reveal the supramolecular architecture or 'molecular sociology' of cells and to discover the unexpected. Here, we review state-of-the-art Cryo-ET workflows, provide examples of biological applications, and discuss what is needed to realize the full potential of Cryo-ET.
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Affiliation(s)
- Martin Turk
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
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8
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Desmosome architecture derived from molecular dynamics simulations and cryo-electron tomography. Proc Natl Acad Sci U S A 2020; 117:27132-27140. [PMID: 33067392 PMCID: PMC7959525 DOI: 10.1073/pnas.2004563117] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The desmosome is a major cell–cell junction connecting cells in tissues under high mechanical load. Currently, while structures of the constituent cadherins are known, the desmosome architecture has remained elusive. The primary reason is the high plasticity of the cadherins. As many other cellular structures, their high flexibility cannot be easily addressed by conventional structural techniques that rely on averaging many identical structures. For this, we combine high-end cryo-electron tomography with large-scale molecular dynamics simulations to produce a molecular model of the desmosome that integrates new with decades-old observations, accounts for the remarkable biophysical properties, and maps the intermolecular interactions. Desmosomes are cell–cell junctions that link tissue cells experiencing intense mechanical stress. Although the structure of the desmosomal cadherins is known, the desmosome architecture—which is essential for mediating numerous functions—remains elusive. Here, we recorded cryo-electron tomograms (cryo-ET) in which individual cadherins can be discerned; they appear variable in shape, spacing, and tilt with respect to the membrane. The resulting sub-tomogram average reaches a resolution of ∼26 Å, limited by the inherent flexibility of desmosomes. To address this challenge typical of dynamic biological assemblies, we combine sub-tomogram averaging with atomistic molecular dynamics (MD) simulations. We generate models of possible cadherin arrangements and perform an in silico screening according to biophysical and structural properties extracted from MD simulation trajectories. We find a truss-like arrangement of cadherins that resembles the characteristic footprint seen in the electron micrograph. The resulting model of the desmosomal architecture explains their unique biophysical properties and strength.
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9
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Wan W, Clarke M, Norris MJ, Kolesnikova L, Koehler A, Bornholdt ZA, Becker S, Saphire EO, Briggs JA. Ebola and Marburg virus matrix layers are locally ordered assemblies of VP40 dimers. eLife 2020; 9:59225. [PMID: 33016878 PMCID: PMC7588233 DOI: 10.7554/elife.59225] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Accepted: 10/02/2020] [Indexed: 01/28/2023] Open
Abstract
Filoviruses such as Ebola and Marburg virus bud from the host membrane as enveloped virions. This process is achieved by the matrix protein VP40. When expressed alone, VP40 induces budding of filamentous virus-like particles, suggesting that localization to the plasma membrane, oligomerization into a matrix layer, and generation of membrane curvature are intrinsic properties of VP40. There has been no direct information on the structure of VP40 matrix layers within viruses or virus-like particles. We present structures of Ebola and Marburg VP40 matrix layers in intact virus-like particles, and within intact Marburg viruses. VP40 dimers assemble extended chains via C-terminal domain interactions. These chains stack to form 2D matrix lattices below the membrane surface. These lattices form a patchwork assembly across the membrane and suggesting that assembly may begin at multiple points. Our observations define the structure and arrangement of the matrix protein layer that mediates formation of filovirus particles.
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Affiliation(s)
- William Wan
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Mairi Clarke
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Michael J Norris
- Center for Infectious Disease and Vaccine Research, La Jolla Institute for Immunology, La Jolla, United States
| | - Larissa Kolesnikova
- Institut für Virologie, Philipps-Universität Marburg, Hans-Meerwein-Straße, Marburg, Germany
| | - Alexander Koehler
- Institut für Virologie, Philipps-Universität Marburg, Hans-Meerwein-Straße, Marburg, Germany
| | | | - Stephan Becker
- Institut für Virologie, Philipps-Universität Marburg, Hans-Meerwein-Straße, Marburg, Germany
| | - Erica Ollmann Saphire
- Center for Infectious Disease and Vaccine Research, La Jolla Institute for Immunology, La Jolla, United States
| | - John Ag Briggs
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
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10
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Mäeots ME, Lee B, Nans A, Jeong SG, Esfahani MMN, Ding S, Smith DJ, Lee CS, Lee SS, Peter M, Enchev RI. Modular microfluidics enables kinetic insight from time-resolved cryo-EM. Nat Commun 2020; 11:3465. [PMID: 32651368 PMCID: PMC7351747 DOI: 10.1038/s41467-020-17230-4] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 06/18/2020] [Indexed: 11/09/2022] Open
Abstract
Mechanistic understanding of biochemical reactions requires structural and kinetic characterization of the underlying chemical processes. However, no single experimental technique can provide this information in a broadly applicable manner and thus structural studies of static macromolecules are often complemented by biophysical analysis. Moreover, the common strategy of utilizing mutants or crosslinking probes to stabilize intermediates is prone to trapping off-pathway artefacts and precludes determining the order of molecular events. Here we report a time-resolved sample preparation method for cryo-electron microscopy (trEM) using a modular microfluidic device, featuring a 3D-mixing unit and variable delay lines that enables automated, fast, and blot-free sample vitrification. This approach not only preserves high-resolution structural detail but also substantially improves sample integrity and protein distribution across the vitreous ice. We validate the method by visualising reaction intermediates of early RecA filament growth across three orders of magnitude on sub-second timescales. The trEM method reported here is versatile, reproducible, and readily adaptable to a broad spectrum of fundamental questions in biology.
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Affiliation(s)
- Märt-Erik Mäeots
- Institute of Biochemistry, Department of Biology, ETH Zurich, Otto-Stern-Weg 3, 8093, Zurich, Switzerland
- The Visual Biochemistry Laboratory, The Francis Crick Institute, 1 Midland Road, NW1 1AT, London, UK
| | - Byungjin Lee
- Department of Chemical Engineering and Applied Chemistry, Chungnam National University, Yuseong-Gu, Daejeon, 305-764, Republic of Korea
| | - Andrea Nans
- Structural Biology Scientific Technology Platform, The Francis Crick Institute, 1 Midland Road, NW1 1AT, London, UK
| | - Seung-Geun Jeong
- Department of Chemical Engineering and Applied Chemistry, Chungnam National University, Yuseong-Gu, Daejeon, 305-764, Republic of Korea
| | - Mohammad M N Esfahani
- The Visual Biochemistry Laboratory, The Francis Crick Institute, 1 Midland Road, NW1 1AT, London, UK
| | - Shan Ding
- The Visual Biochemistry Laboratory, The Francis Crick Institute, 1 Midland Road, NW1 1AT, London, UK
| | - Daniel J Smith
- Institute of Biochemistry, Department of Biology, ETH Zurich, Otto-Stern-Weg 3, 8093, Zurich, Switzerland
- Scientific Center for Optical and Electron Microscopy, ETH Zurich, Otto-Stern-Weg 3, 8093, Zurich, Switzerland
| | - Chang-Soo Lee
- Department of Chemical Engineering and Applied Chemistry, Chungnam National University, Yuseong-Gu, Daejeon, 305-764, Republic of Korea.
| | - Sung Sik Lee
- Institute of Biochemistry, Department of Biology, ETH Zurich, Otto-Stern-Weg 3, 8093, Zurich, Switzerland.
- Scientific Center for Optical and Electron Microscopy, ETH Zurich, Otto-Stern-Weg 3, 8093, Zurich, Switzerland.
| | - Matthias Peter
- Institute of Biochemistry, Department of Biology, ETH Zurich, Otto-Stern-Weg 3, 8093, Zurich, Switzerland.
| | - Radoslav I Enchev
- Institute of Biochemistry, Department of Biology, ETH Zurich, Otto-Stern-Weg 3, 8093, Zurich, Switzerland.
- The Visual Biochemistry Laboratory, The Francis Crick Institute, 1 Midland Road, NW1 1AT, London, UK.
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11
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Aparicio D, Scheffer MP, Marcos-Silva M, Vizarraga D, Sprankel L, Ratera M, Weber MS, Seybert A, Torres-Puig S, Gonzalez-Gonzalez L, Reitz J, Querol E, Piñol J, Pich OQ, Fita I, Frangakis AS. Structure and mechanism of the Nap adhesion complex from the human pathogen Mycoplasma genitalium. Nat Commun 2020; 11:2877. [PMID: 32513917 PMCID: PMC7280502 DOI: 10.1038/s41467-020-16511-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Accepted: 05/06/2020] [Indexed: 11/09/2022] Open
Abstract
Mycoplasma genitalium is a human pathogen adhering to host target epithelial cells and causing urethritis, cervicitis and pelvic inflammatory disease. Essential for infectivity is a transmembrane adhesion complex called Nap comprising proteins P110 and P140. Here we report the crystal structure of P140 both alone and in complex with the N-terminal domain of P110. By cryo-electron microscopy (cryo-EM) and tomography (cryo-ET) we find closed and open Nap conformations, determined at 9.8 and 15 Å, respectively. Both crystal structures and the cryo-EM structure are found in a closed conformation, where the sialic acid binding site in P110 is occluded. By contrast, the cryo-ET structure shows an open conformation, where the binding site is accessible. Structural information, in combination with functional studies, suggests a mechanism for attachment and release of M. genitalium to and from the host cell receptor, in which Nap conformations alternate to sustain motility and guarantee infectivity.
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Affiliation(s)
- David Aparicio
- Instituto de Biología Molecular de Barcelona (IBMB-CSIC) and Maria de Maeztu Unit of Excellence, Parc Científic de Barcelona, Baldiri Reixac 10, 08028, Barcelona, Spain
| | - Margot P Scheffer
- Buchmann Institute for Molecular Life Sciences, Max-von-Laue Str. 15, 60438, Frankfurt, Germany
| | - Marina Marcos-Silva
- Institut de Biotecnologia i Biomedicina and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, Bellaterra, 08193, Barcelona, Spain
| | - David Vizarraga
- Instituto de Biología Molecular de Barcelona (IBMB-CSIC) and Maria de Maeztu Unit of Excellence, Parc Científic de Barcelona, Baldiri Reixac 10, 08028, Barcelona, Spain
| | - Lasse Sprankel
- Buchmann Institute for Molecular Life Sciences, Max-von-Laue Str. 15, 60438, Frankfurt, Germany
| | - Mercè Ratera
- Instituto de Biología Molecular de Barcelona (IBMB-CSIC) and Maria de Maeztu Unit of Excellence, Parc Científic de Barcelona, Baldiri Reixac 10, 08028, Barcelona, Spain
| | - Miriam S Weber
- Buchmann Institute for Molecular Life Sciences, Max-von-Laue Str. 15, 60438, Frankfurt, Germany
| | - Anja Seybert
- Buchmann Institute for Molecular Life Sciences, Max-von-Laue Str. 15, 60438, Frankfurt, Germany
| | - Sergi Torres-Puig
- Institut de Biotecnologia i Biomedicina and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, Bellaterra, 08193, Barcelona, Spain
| | - Luis Gonzalez-Gonzalez
- Institut de Biotecnologia i Biomedicina and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, Bellaterra, 08193, Barcelona, Spain
| | - Julian Reitz
- Buchmann Institute for Molecular Life Sciences, Max-von-Laue Str. 15, 60438, Frankfurt, Germany
| | - Enrique Querol
- Institut de Biotecnologia i Biomedicina and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, Bellaterra, 08193, Barcelona, Spain
| | - Jaume Piñol
- Institut de Biotecnologia i Biomedicina and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, Bellaterra, 08193, Barcelona, Spain
| | - Oscar Q Pich
- Institut de Biotecnologia i Biomedicina and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, Bellaterra, 08193, Barcelona, Spain.
| | - Ignacio Fita
- Instituto de Biología Molecular de Barcelona (IBMB-CSIC) and Maria de Maeztu Unit of Excellence, Parc Científic de Barcelona, Baldiri Reixac 10, 08028, Barcelona, Spain.
| | - Achilleas S Frangakis
- Buchmann Institute for Molecular Life Sciences, Max-von-Laue Str. 15, 60438, Frankfurt, Germany.
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12
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Riesterer JL, López CS, Stempinski ES, Williams M, Loftis K, Stoltz K, Thibault G, Lanicault C, Williams T, Gray JW. A workflow for visualizing human cancer biopsies using large-format electron microscopy. Methods Cell Biol 2020; 158:163-181. [PMID: 32423648 DOI: 10.1016/bs.mcb.2020.01.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Recent developments in large format electron microscopy have enabled generation of images that provide detailed ultrastructural information on normal and diseased cells and tissues. Analyses of these images increase our understanding of cellular organization and interactions and disease-related changes therein. In this manuscript, we describe a workflow for two-dimensional (2D) and three-dimensional (3D) imaging, including both optical and scanning electron microscopy (SEM) methods, that allow pathologists and cancer biology researchers to identify areas of interest from human cancer biopsies. The protocols and mounting strategies described in this workflow are compatible with 2D large format EM mapping, 3D focused ion beam-SEM and serial block face-SEM. The flexibility to use diverse imaging technologies available at most academic institutions makes this workflow useful and applicable for most life science samples. Volumetric analysis of the biopsies studied here revealed morphological, organizational and ultrastructural aspects of the tumor cells and surrounding environment that cannot be revealed by conventional 2D EM imaging. Our results indicate that although 2D EM is still an important tool in many areas of diagnostic pathology, 3D images of ultrastructural relationships between both normal and cancerous cells, in combination with their extracellular matrix, enables cancer researchers and pathologists to better understand the progression of the disease and identify potential therapeutic targets.
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Affiliation(s)
- Jessica L Riesterer
- OHSU Center for Spatial Systems Biomedicine, Oregon Health and Sciences University, Portland, OR, United States; Multiscale Microscopy Core, Oregon Health and Sciences University, Portland, OR, United States.
| | - Claudia S López
- OHSU Center for Spatial Systems Biomedicine, Oregon Health and Sciences University, Portland, OR, United States; Multiscale Microscopy Core, Oregon Health and Sciences University, Portland, OR, United States; Pacific Northwest Center for CryoEM, Oregon Health and Sciences University, Portland, OR, United States.
| | - Erin S Stempinski
- OHSU Center for Spatial Systems Biomedicine, Oregon Health and Sciences University, Portland, OR, United States; Multiscale Microscopy Core, Oregon Health and Sciences University, Portland, OR, United States
| | - Melissa Williams
- OHSU Center for Spatial Systems Biomedicine, Oregon Health and Sciences University, Portland, OR, United States; Multiscale Microscopy Core, Oregon Health and Sciences University, Portland, OR, United States
| | - Kevin Loftis
- OHSU Center for Spatial Systems Biomedicine, Oregon Health and Sciences University, Portland, OR, United States
| | - Kevin Stoltz
- OHSU Center for Spatial Systems Biomedicine, Oregon Health and Sciences University, Portland, OR, United States
| | - Guillaume Thibault
- OHSU Center for Spatial Systems Biomedicine, Oregon Health and Sciences University, Portland, OR, United States
| | - Christian Lanicault
- Department of Pathology, Oregon Health and Sciences University, Portland, OR, United States
| | - Todd Williams
- Department of Pathology, Oregon Health and Sciences University, Portland, OR, United States
| | - Joe W Gray
- OHSU Center for Spatial Systems Biomedicine, Oregon Health and Sciences University, Portland, OR, United States.
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13
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Dick RA, Xu C, Morado DR, Kravchuk V, Ricana CL, Lyddon TD, Broad AM, Feathers JR, Johnson MC, Vogt VM, Perilla JR, Briggs JAG, Schur FKM. Structures of immature EIAV Gag lattices reveal a conserved role for IP6 in lentivirus assembly. PLoS Pathog 2020; 16:e1008277. [PMID: 31986188 PMCID: PMC7004409 DOI: 10.1371/journal.ppat.1008277] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 02/06/2020] [Accepted: 12/11/2019] [Indexed: 01/11/2023] Open
Abstract
Retrovirus assembly is driven by the multidomain structural protein Gag. Interactions between the capsid domains (CA) of Gag result in Gag multimerization, leading to an immature virus particle that is formed by a protein lattice based on dimeric, trimeric, and hexameric protein contacts. Among retroviruses the inter- and intra-hexamer contacts differ, especially in the N-terminal sub-domain of CA (CANTD). For HIV-1 the cellular molecule inositol hexakisphosphate (IP6) interacts with and stabilizes the immature hexamer, and is required for production of infectious virus particles. We have used in vitro assembly, cryo-electron tomography and subtomogram averaging, atomistic molecular dynamics simulations and mutational analyses to study the HIV-related lentivirus equine infectious anemia virus (EIAV). In particular, we sought to understand the structural conservation of the immature lentivirus lattice and the role of IP6 in EIAV assembly. Similar to HIV-1, IP6 strongly promoted in vitro assembly of EIAV Gag proteins into virus-like particles (VLPs), which took three morphologically highly distinct forms: narrow tubes, wide tubes, and spheres. Structural characterization of these VLPs to sub-4Å resolution unexpectedly showed that all three morphologies are based on an immature lattice with preserved key structural components, highlighting the structural versatility of CA to form immature assemblies. A direct comparison between EIAV and HIV revealed that both lentiviruses maintain similar immature interfaces, which are established by both conserved and non-conserved residues. In both EIAV and HIV-1, IP6 regulates immature assembly via conserved lysine residues within the CACTD and SP. Lastly, we demonstrate that IP6 stimulates in vitro assembly of immature particles of several other retroviruses in the lentivirus genus, suggesting a conserved role for IP6 in lentiviral assembly.
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MESH Headings
- Amino Acid Sequence
- Animals
- Electron Microscope Tomography
- Equine Infectious Anemia/metabolism
- Equine Infectious Anemia/virology
- Gene Products, gag/chemistry
- Gene Products, gag/genetics
- Gene Products, gag/metabolism
- HIV Infections/metabolism
- HIV Infections/virology
- HIV-1/genetics
- HIV-1/physiology
- HIV-1/ultrastructure
- Horses
- Host-Pathogen Interactions
- Infectious Anemia Virus, Equine/chemistry
- Infectious Anemia Virus, Equine/genetics
- Infectious Anemia Virus, Equine/physiology
- Infectious Anemia Virus, Equine/ultrastructure
- Phytic Acid/metabolism
- Sequence Alignment
- Virion/genetics
- Virion/physiology
- Virion/ultrastructure
- Virus Assembly
- gag Gene Products, Human Immunodeficiency Virus/chemistry
- gag Gene Products, Human Immunodeficiency Virus/genetics
- gag Gene Products, Human Immunodeficiency Virus/metabolism
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Affiliation(s)
- Robert A. Dick
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
- * E-mail: (RAD); (FKMS)
| | - Chaoyi Xu
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, United States of America
| | - Dustin R. Morado
- Structural Studies Division, Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
| | | | - Clifton L. Ricana
- Department of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri, United States of America
| | - Terri D. Lyddon
- Department of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri, United States of America
| | - Arianna M. Broad
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - J. Ryan Feathers
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Marc C. Johnson
- Department of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri, United States of America
| | - Volker M. Vogt
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Juan R. Perilla
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, United States of America
| | - John A. G. Briggs
- Structural Studies Division, Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Florian K. M. Schur
- Institute of Science and Technology Austria, Klosterneuburg, Austria
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
- * E-mail: (RAD); (FKMS)
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14
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Dimers of mitochondrial ATP synthase induce membrane curvature and self-assemble into rows. Proc Natl Acad Sci U S A 2019; 116:4250-4255. [PMID: 30760595 PMCID: PMC6410833 DOI: 10.1073/pnas.1816556116] [Citation(s) in RCA: 167] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The ATP synthase in the inner membrane of mitochondria generates most of the ATP that enables higher organisms to live. The inner membrane forms deep invaginations called cristae. Mitochondrial ATP synthases are dimeric complexes of two identical monomers. It is known that the ATP synthase dimers form rows along the tightly curved cristae ridges. Computer simulations suggest that the dimer rows bend the membrane locally, but this has not been shown experimentally. In this study, we use electron cryotomography to provide experimental proof that ATP synthase dimers assemble spontaneously into rows upon membrane reconstitution, and that these rows bend the membrane. The assembly of ATP synthase dimers into rows is most likely the first step in the formation of mitochondrial cristae. Mitochondrial ATP synthases form dimers, which assemble into long ribbons at the rims of the inner membrane cristae. We reconstituted detergent-purified mitochondrial ATP synthase dimers from the green algae Polytomella sp. and the yeast Yarrowia lipolytica into liposomes and examined them by electron cryotomography. Tomographic volumes revealed that ATP synthase dimers from both species self-assemble into rows and bend the lipid bilayer locally. The dimer rows and the induced degree of membrane curvature closely resemble those in the inner membrane cristae. Monomers of mitochondrial ATP synthase reconstituted into liposomes do not bend membrane visibly and do not form rows. No specific lipids or proteins other than ATP synthase dimers are required for row formation and membrane remodelling. Long rows of ATP synthase dimers are a conserved feature of mitochondrial inner membranes. They are required for cristae formation and a main factor in mitochondrial morphogenesis.
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15
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16
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Goswami P, Abid Ali F, Douglas ME, Locke J, Purkiss A, Janska A, Eickhoff P, Early A, Nans A, Cheung AMC, Diffley JFX, Costa A. Structure of DNA-CMG-Pol epsilon elucidates the roles of the non-catalytic polymerase modules in the eukaryotic replisome. Nat Commun 2018; 9:5061. [PMID: 30498216 PMCID: PMC6265327 DOI: 10.1038/s41467-018-07417-1] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Accepted: 10/28/2018] [Indexed: 12/12/2022] Open
Abstract
Eukaryotic origin firing depends on assembly of the Cdc45-MCM-GINS (CMG) helicase. A key step is the recruitment of GINS that requires the leading-strand polymerase Pol epsilon, composed of Pol2, Dpb2, Dpb3, Dpb4. While a truncation of the catalytic N-terminal Pol2 supports cell division, Dpb2 and C-terminal Pol2 (C-Pol2) are essential for viability. Dpb2 and C-Pol2 are non-catalytic modules, shown or predicted to be related to an exonuclease and DNA polymerase, respectively. Here, we present the cryo-EM structure of the isolated C-Pol2/Dpb2 heterodimer, revealing that C-Pol2 contains a DNA polymerase fold. We also present the structure of CMG/C-Pol2/Dpb2 on a DNA fork, and find that polymerase binding changes both the helicase structure and fork-junction engagement. Inter-subunit contacts that keep the helicase-polymerase complex together explain several cellular phenotypes. At least some of these contacts are preserved during Pol epsilon-dependent CMG assembly on path to origin firing, as observed with DNA replication reconstituted in vitro. Eukaryotic origin firing depends on assembly of the Cdc45-MCM-GINS (CMG) helicase, which requires the leading-strand polymerase Pol ɛ. Here the authors present a structural analysis of a CMG Pol ɛ on a DNA fork, providing insight on the steps leading productive helicase engagement to the DNA junction.
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Affiliation(s)
- Panchali Goswami
- Macromolecular Machines Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Ferdos Abid Ali
- Macromolecular Machines Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Max E Douglas
- Chromosome Replication Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Julia Locke
- Macromolecular Machines Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Andrew Purkiss
- Structural Biology Science Technology Platform, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Agnieszka Janska
- Chromosome Replication Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Patrik Eickhoff
- Macromolecular Machines Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Anne Early
- Chromosome Replication Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Andrea Nans
- Structural Biology Science Technology Platform, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Alan M C Cheung
- Department of Structural and Molecular Biology, Institute of Structural and Molecular Biology, University College London, London, UK.,Institute of Structural and Molecular Biology, Biological Sciences, Birkbeck College, London, WC1E 7HX, UK
| | - John F X Diffley
- Chromosome Replication Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Alessandro Costa
- Macromolecular Machines Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK.
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17
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Abstract
Immature retroviruses are built by the Gag polyprotein; Gag is then cut into domains, and the resulting CA capsid proteins form the mature capsid, which can mediate infection of a new cell. Murine leukemia virus (MLV) is a model retrovirus and the basis for gene-delivery vectors. We determined the capsid structures and architectures for immature and mature MLV. The mature MLV core does not enclose the genome in a closed capsid by using only part of the available proteins, as is the case for HIV-1. Instead, it wraps the genome in curved sheets incorporating most CA proteins. Retroviruses therefore have fundamentally different modes of core assembly and genome protection, which may relate to differences in their early replication. Retroviruses assemble and bud from infected cells in an immature form and require proteolytic maturation for infectivity. The CA (capsid) domains of the Gag polyproteins assemble a protein lattice as a truncated sphere in the immature virion. Proteolytic cleavage of Gag induces dramatic structural rearrangements; a subset of cleaved CA subsequently assembles into the mature core, whose architecture varies among retroviruses. Murine leukemia virus (MLV) is the prototypical γ-retrovirus and serves as the basis of retroviral vectors, but the structure of the MLV CA layer is unknown. Here we have combined X-ray crystallography with cryoelectron tomography to determine the structures of immature and mature MLV CA layers within authentic viral particles. This reveals the structural changes associated with maturation, and, by comparison with HIV-1, uncovers conserved and variable features. In contrast to HIV-1, most MLV CA is used for assembly of the mature core, which adopts variable, multilayered morphologies and does not form a closed structure. Unlike in HIV-1, there is similarity between protein–protein interfaces in the immature MLV CA layer and those in the mature CA layer, and structural maturation of MLV could be achieved through domain rotations that largely maintain hexameric interactions. Nevertheless, the dramatic architectural change on maturation indicates that extensive disassembly and reassembly are required for mature core growth. The core morphology suggests that wrapping of the genome in CA sheets may be sufficient to protect the MLV ribonucleoprotein during cell entry.
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18
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Picco A, Kukulski W, Manenschijn HE, Specht T, Briggs JAG, Kaksonen M. The contributions of the actin machinery to endocytic membrane bending and vesicle formation. Mol Biol Cell 2018; 29:1346-1358. [PMID: 29851558 PMCID: PMC5994895 DOI: 10.1091/mbc.e17-11-0688] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Branched and cross-linked actin networks mediate cellular processes that move and shape membranes. To understand how actin contributes during the different stages of endocytic membrane reshaping, we analyzed deletion mutants of yeast actin network components using a hybrid imaging approach that combines live imaging with correlative microscopy. We could thus temporally dissect the effects of different actin network perturbations, revealing distinct stages of actin-based membrane reshaping. Our data show that initiation of membrane bending requires the actin network to be physically linked to the plasma membrane and to be optimally cross-linked. Once initiated, the membrane invagination process is driven by nucleation and polymerization of new actin filaments, independent of the degree of cross-linking and unaffected by a surplus of actin network components. A key transition occurs 2 s before scission, when the filament nucleation rate drops. From that time point on, invagination growth and vesicle scission are driven by an expansion of the actin network without a proportional increase of net actin amounts. The expansion is sensitive to the amount of filamentous actin and its cross-linking. Our results suggest that the mechanism by which actin reshapes the membrane changes during the progress of endocytosis, possibly adapting to varying force requirements.
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Affiliation(s)
- Andrea Picco
- Department of Biochemistry and NCCR Chemical Biology, University of Geneva, 1211 Geneva, Switzerland
| | - Wanda Kukulski
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.,Structural and Computational Biology Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.,Cell Biology Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
| | - Hetty E Manenschijn
- Department of Biochemistry and NCCR Chemical Biology, University of Geneva, 1211 Geneva, Switzerland.,Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
| | - Tanja Specht
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
| | - John A G Briggs
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.,Structural and Computational Biology Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.,Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
| | - Marko Kaksonen
- Department of Biochemistry and NCCR Chemical Biology, University of Geneva, 1211 Geneva, Switzerland
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19
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Seybert A, Gonzalez-Gonzalez L, Scheffer MP, Lluch-Senar M, Mariscal AM, Querol E, Matthaeus F, Piñol J, Frangakis AS. Cryo-electron tomography analyses of terminal organelle mutants suggest the motility mechanism of Mycoplasma genitalium. Mol Microbiol 2018; 108:319-329. [PMID: 29470847 DOI: 10.1111/mmi.13938] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/20/2018] [Indexed: 11/28/2022]
Abstract
The terminal organelle of Mycoplasma genitalium is responsible for bacterial adhesion, motility and pathogenicity. Localized at the cell tip, it comprises an electron-dense core that is anchored to the cell membrane at its distal end and to the cytoplasm at its proximal end. The surface of the terminal organelle is also covered with adhesion proteins. We performed cellular cryoelectron tomography on deletion mutants of eleven proteins that are implicated in building the terminal organelle, to systematically analyze the ultrastructural effects. These data were correlated with microcinematographies, from which the motility patterns can be quantitatively assessed. We visualized diverse phenotypes, ranging from mild to severe cell adhesion, motility and segregation defects. Based on our observations, we propose a double-spring ratchet model for the motility mechanism that explains our current and previous observations. Our model, which expands and integrates the previously suggested inchworm model, allocates specific functions to each of the essential components of this unique bacterial motility system.
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Affiliation(s)
- Anja Seybert
- Buchmann Institute for Molecular Life Sciences and Institute of Biophysics, Goethe University Frankfurt, Max-von-Laue Str. 15, Frankfurt 60438, Germany
| | - Luis Gonzalez-Gonzalez
- Departament de Bioquímica i Biologia Molecular and Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès 08193, Spain
| | - Margot P Scheffer
- Buchmann Institute for Molecular Life Sciences and Institute of Biophysics, Goethe University Frankfurt, Max-von-Laue Str. 15, Frankfurt 60438, Germany
| | - Maria Lluch-Senar
- Departament de Bioquímica i Biologia Molecular and Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès 08193, Spain
| | - Ana M Mariscal
- Departament de Bioquímica i Biologia Molecular and Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès 08193, Spain
| | - Enrique Querol
- Departament de Bioquímica i Biologia Molecular and Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès 08193, Spain
| | - Franziska Matthaeus
- Faculty of Biological Sciences & FIAS, Goethe University Frankfurt, Ruth-Moufang-Straße 1, Frankfurt 60438, Germany
| | - Jaume Piñol
- Departament de Bioquímica i Biologia Molecular and Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès 08193, Spain
| | - Achilleas S Frangakis
- Buchmann Institute for Molecular Life Sciences and Institute of Biophysics, Goethe University Frankfurt, Max-von-Laue Str. 15, Frankfurt 60438, Germany
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20
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Wan W, Kolesnikova L, Clarke M, Koehler A, Noda T, Becker S, Briggs JAG. Structure and assembly of the Ebola virus nucleocapsid. Nature 2017; 551:394-397. [PMID: 29144446 PMCID: PMC5714281 DOI: 10.1038/nature24490] [Citation(s) in RCA: 132] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Accepted: 10/04/2017] [Indexed: 12/11/2022]
Abstract
Ebola and Marburg viruses are filoviruses: filamentous, enveloped viruses that cause haemorrhagic fever. Filoviruses are within the order Mononegavirales, which also includes rabies virus, measles virus, and respiratory syncytial virus. Mononegaviruses have non-segmented, single-stranded negative-sense RNA genomes that are encapsidated by nucleoprotein and other viral proteins to form a helical nucleocapsid. The nucleocapsid acts as a scaffold for virus assembly and as a template for genome transcription and replication. Insights into nucleoprotein-nucleoprotein interactions have been derived from structural studies of oligomerized, RNA-encapsidating nucleoprotein, and cryo-electron microscopy of nucleocapsid or nucleocapsid-like structures. There have been no high-resolution reconstructions of complete mononegavirus nucleocapsids. Here we apply cryo-electron tomography and subtomogram averaging to determine the structure of Ebola virus nucleocapsid within intact viruses and recombinant nucleocapsid-like assemblies. These structures reveal the identity and arrangement of the nucleocapsid components, and suggest that the formation of an extended α-helix from the disordered carboxy-terminal region of nucleoprotein-core links nucleoprotein oligomerization, nucleocapsid condensation, RNA encapsidation, and accessory protein recruitment.
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Affiliation(s)
- William Wan
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Larissa Kolesnikova
- Institut für Virologie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg, Germany
| | - Mairi Clarke
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Alexander Koehler
- Institut für Virologie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg, Germany
| | - Takeshi Noda
- Laboratory of Ultrastructural virology, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto, Japan; PRESTO, Japan Science and Technology Agency, Saitama, Japan
| | - Stephan Becker
- Institut für Virologie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg, Germany
| | - John A. G. Briggs
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
- Structural Studies Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
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21
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Scheffer MP, Gonzalez-Gonzalez L, Seybert A, Ratera M, Kunz M, Valpuesta JM, Fita I, Querol E, Piñol J, Martín-Benito J, Frangakis AS. Structural characterization of the NAP; the major adhesion complex of the human pathogen Mycoplasma genitalium. Mol Microbiol 2017; 105:869-879. [PMID: 28671286 DOI: 10.1111/mmi.13743] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/29/2017] [Indexed: 01/09/2023]
Abstract
Mycoplasma genitalium, the causative agent of non-gonococcal urethritis and pelvic inflammatory disease in humans, is a small eubacterium that lacks a peptidoglycan cell wall. On the surface of its plasma membrane is the major surface adhesion complex, known as NAP that is essential for adhesion and gliding motility of the organism. Here, we have performed cryo-electron tomography of intact cells and detergent permeabilized M. genitalium cell aggregates, providing sub-tomogram averages of free and cell-attached NAPs respectively, revealing a tetrameric complex with two-fold rotational (C2) symmetry. Each NAP has two pairs of globular lobes (named α and β lobes), arranged as a dimer of heterodimers with each lobe connected by a stalk to the cell membrane. The β lobes are larger than the α lobes by 20%. Classification of NAPs showed that the complex can tilt with respect to the cell membrane. A protein complex containing exclusively the proteins P140 and P110, was purified from M. genitalium and was structurally characterized by negative-stain single particle EM reconstruction. The close structural similarity found between intact NAPs and the isolated P140/P110 complexes, shows that dimers of P140/P110 heterodimers are the only components of the extracellular region of intact NAPs in M. genitalium.
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Affiliation(s)
- Margot P Scheffer
- Buchmann Institute for Molecular Life Sciences, Goethe University Frankfurt, Max-von-Laue Str. 15, Frankfurt 60438, Germany
| | - Luis Gonzalez-Gonzalez
- Departament de Bioquímica i Biologia Molecular and Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès 08193, Spain
| | - Anja Seybert
- Buchmann Institute for Molecular Life Sciences, Goethe University Frankfurt, Max-von-Laue Str. 15, Frankfurt 60438, Germany
| | - Mercè Ratera
- Parc Científic de Barcelona, Instituto de Biología Molecular de Barcelona del (IBMB-CSIC), Baldiri i Reixac 10, Barcelona 08028, Spain
| | - Michael Kunz
- Buchmann Institute for Molecular Life Sciences, Goethe University Frankfurt, Max-von-Laue Str. 15, Frankfurt 60438, Germany
| | - José M Valpuesta
- Department for Macromolecular Structures, Centro Nacional de Biotecnologıa (CNB-CSIC), Madrid 28049, Spain
| | - Ignacio Fita
- Parc Científic de Barcelona, Instituto de Biología Molecular de Barcelona del (IBMB-CSIC), Baldiri i Reixac 10, Barcelona 08028, Spain
| | - Enrique Querol
- Departament de Bioquímica i Biologia Molecular and Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès 08193, Spain
| | - Jaume Piñol
- Departament de Bioquímica i Biologia Molecular and Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès 08193, Spain
| | - Jaime Martín-Benito
- Department for Macromolecular Structures, Centro Nacional de Biotecnologıa (CNB-CSIC), Madrid 28049, Spain
| | - Achilleas S Frangakis
- Buchmann Institute for Molecular Life Sciences, Goethe University Frankfurt, Max-von-Laue Str. 15, Frankfurt 60438, Germany
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22
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Mattei S, Glass B, Hagen WJH, Kräusslich HG, Briggs JAG. The structure and flexibility of conical HIV-1 capsids determined within intact virions. Science 2017; 354:1434-1437. [PMID: 27980210 DOI: 10.1126/science.aah4972] [Citation(s) in RCA: 181] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Accepted: 11/18/2016] [Indexed: 12/30/2022]
Abstract
HIV-1 contains a cone-shaped capsid encasing the viral genome. This capsid is thought to follow fullerene geometry-a curved hexameric lattice of the capsid protein, CA, closed by incorporating 12 CA pentamers. Current models for core structure are based on crystallography of hexameric and cross-linked pentameric CA, electron microscopy of tubular CA arrays, and simulations. Here, we report subnanometer-resolution cryo-electron tomography structures of hexameric and pentameric CA within intact HIV-1 particles. Whereas the hexamer structure is compatible with crystallography studies, the pentamer forms using different interfaces. Determining multiple structures revealed how CA flexes to form the variably curved core shell. We show that HIV-1 CA assembles both aberrant and perfect fullerene cones, supporting models in which conical cores assemble de novo after maturation.
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Affiliation(s)
- Simone Mattei
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.,Molecular Medicine Partnership Unit, European Molecular Biology Laboratory-Universitätsklinikum Heidelberg, Heidelberg, Germany
| | - Bärbel Glass
- Department of Infectious Diseases, Virology, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Wim J H Hagen
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Hans-Georg Kräusslich
- Molecular Medicine Partnership Unit, European Molecular Biology Laboratory-Universitätsklinikum Heidelberg, Heidelberg, Germany.,Department of Infectious Diseases, Virology, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - John A G Briggs
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany. .,Molecular Medicine Partnership Unit, European Molecular Biology Laboratory-Universitätsklinikum Heidelberg, Heidelberg, Germany
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23
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In situ structure of trypanosomal ATP synthase dimer reveals a unique arrangement of catalytic subunits. Proc Natl Acad Sci U S A 2017; 114:992-997. [PMID: 28096380 DOI: 10.1073/pnas.1612386114] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
We used electron cryotomography and subtomogram averaging to determine the in situ structures of mitochondrial ATP synthase dimers from two organisms belonging to the phylum euglenozoa: Trypanosoma brucei, a lethal human parasite, and Euglena gracilis, a photosynthetic protist. At a resolution of 32.5 Å and 27.5 Å, respectively, the two structures clearly exhibit a noncanonical F1 head, in which the catalytic (αβ)3 assembly forms a triangular pyramid rather than the pseudo-sixfold ring arrangement typical of all other ATP synthases investigated so far. Fitting of known X-ray structures reveals that this unusual geometry results from a phylum-specific cleavage of the α subunit, in which the C-terminal αC fragments are displaced by ∼20 Å and rotated by ∼30° from their expected positions. In this location, the αC fragment is unable to form the conserved catalytic interface that was thought to be essential for ATP synthesis, and cannot convert γ-subunit rotation into the conformational changes implicit in rotary catalysis. The new arrangement of catalytic subunits suggests that the mechanism of ATP generation by rotary ATPases is less strictly conserved than has been generally assumed. The ATP synthases of these organisms present a unique model system for discerning the individual contributions of the α and β subunits to the fundamental process of ATP synthesis.
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24
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Structure of RNA polymerase I transcribing ribosomal DNA genes. Nature 2016; 540:607-610. [PMID: 27842382 DOI: 10.1038/nature20561] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 10/25/2016] [Indexed: 11/08/2022]
Abstract
RNA polymerase I (Pol I) is a highly processive enzyme that transcribes ribosomal DNA (rDNA) and regulates growth of eukaryotic cells. Crystal structures of free Pol I from the yeast Saccharomyces cerevisiae have revealed dimers of the enzyme stabilized by a 'connector' element and an expanded cleft containing the active centre in an inactive conformation. The central bridge helix was unfolded and a Pol-I-specific 'expander' element occupied the DNA-template-binding site. The structure of Pol I in its active transcribing conformation has yet to be determined, whereas structures of Pol II and Pol III have been solved with bound DNA template and RNA transcript. Here we report structures of active transcribing Pol I from yeast solved by two different cryo-electron microscopy approaches. A single-particle structure at 3.8 Å resolution reveals a contracted active centre cleft with bound DNA and RNA, and a narrowed pore beneath the active site that no longer holds the RNA-cleavage-stimulating domain of subunit A12.2. A structure at 29 Å resolution that was determined from cryo-electron tomograms of Pol I enzymes transcribing cellular rDNA confirms contraction of the cleft and reveals that incoming and exiting rDNA enclose an angle of around 150°. The structures suggest a model for the regulation of transcription elongation in which contracted and expanded polymerase conformations are associated with active and inactive states, respectively.
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25
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Otsuka S, Bui KH, Schorb M, Hossain MJ, Politi AZ, Koch B, Eltsov M, Beck M, Ellenberg J. Nuclear pore assembly proceeds by an inside-out extrusion of the nuclear envelope. eLife 2016; 5. [PMID: 27630123 PMCID: PMC5065316 DOI: 10.7554/elife.19071] [Citation(s) in RCA: 117] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 09/13/2016] [Indexed: 01/01/2023] Open
Abstract
The nuclear pore complex (NPC) mediates nucleocytoplasmic transport through the nuclear envelope. How the NPC assembles into this double membrane boundary has remained enigmatic. Here, we captured temporally staged assembly intermediates by correlating live cell imaging with high-resolution electron tomography and super-resolution microscopy. Intermediates were dome-shaped evaginations of the inner nuclear membrane (INM), that grew in diameter and depth until they fused with the flat outer nuclear membrane. Live and super-resolved fluorescence microscopy revealed the molecular maturation of the intermediates, which initially contained the nuclear and cytoplasmic ring component Nup107, and only later the cytoplasmic filament component Nup358. EM particle averaging showed that the evagination base was surrounded by an 8-fold rotationally symmetric ring structure from the beginning and that a growing mushroom-shaped density was continuously associated with the deforming membrane. Quantitative structural analysis revealed that interphase NPC assembly proceeds by an asymmetric inside-out extrusion of the INM.
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Affiliation(s)
- Shotaro Otsuka
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Khanh Huy Bui
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Martin Schorb
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Electron Microscopy Core Facility, European Molecular Biology Laboratory, Heidelberg, Germany
| | - M Julius Hossain
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Antonio Z Politi
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Birgit Koch
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Mikhail Eltsov
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Martin Beck
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Jan Ellenberg
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
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26
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Darrow MC, Zhang Y, Cinquin BP, Smith EA, Boudreau R, Rochat RH, Schmid MF, Xia Y, Larabell CA, Chiu W. Visualizing red blood cell sickling and the effects of inhibition of sphingosine kinase 1 using soft X-ray tomography. J Cell Sci 2016; 129:3511-7. [PMID: 27505892 DOI: 10.1242/jcs.189225] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Accepted: 08/01/2016] [Indexed: 01/17/2023] Open
Abstract
Sickle cell disease is a destructive genetic disorder characterized by the formation of fibrils of deoxygenated hemoglobin, leading to the red blood cell (RBC) morphology changes that underlie the clinical manifestations of this disease. Using cryogenic soft X-ray tomography (SXT), we characterized the morphology of sickled RBCs in terms of volume and the number of protrusions per cell. We were able to identify statistically a relationship between the number of protrusions and the volume of the cell, which is known to correlate to the severity of sickling. This structural polymorphism allows for the classification of the stages of the sickling process. Recent studies have shown that elevated sphingosine kinase 1 (Sphk1)-mediated sphingosine 1-phosphate production contributes to sickling. Here, we further demonstrate that compound 5C, an inhibitor of Sphk1, has anti-sickling properties. Additionally, the variation in cellular morphology upon treatment suggests that this drug acts to delay the sickling process. SXT is an effective tool that can be used to identify the morphology of the sickling process and assess the effectiveness of potential therapeutics.
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Affiliation(s)
- Michele C Darrow
- National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Yujin Zhang
- Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Bertrand P Cinquin
- Department of Anatomy, University of California San Francisco, San Francisco, CA 94143, USA Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Elizabeth A Smith
- Department of Anatomy, University of California San Francisco, San Francisco, CA 94143, USA Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Rosanne Boudreau
- Department of Anatomy, University of California San Francisco, San Francisco, CA 94143, USA Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Ryan H Rochat
- National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Michael F Schmid
- National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Yang Xia
- Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA University of Texas at Houston Graduate School of Biomedical Sciences, Houston, TX 77030, USA Department of Nephrology, The First Xiangya Hospital, Central South University, Changsha, Hunan 410008, People's Republic of China
| | - Carolyn A Larabell
- Department of Anatomy, University of California San Francisco, San Francisco, CA 94143, USA Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Wah Chiu
- National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
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27
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Schur FKM, Obr M, Hagen WJH, Wan W, Jakobi AJ, Kirkpatrick JM, Sachse C, Kräusslich HG, Briggs JAG. An atomic model of HIV-1 capsid-SP1 reveals structures regulating assembly and maturation. Science 2016; 353:506-8. [PMID: 27417497 DOI: 10.1126/science.aaf9620] [Citation(s) in RCA: 291] [Impact Index Per Article: 36.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 06/29/2016] [Indexed: 12/28/2022]
Abstract
Immature HIV-1 assembles at and buds from the plasma membrane before proteolytic cleavage of the viral Gag polyprotein induces structural maturation. Maturation can be blocked by maturation inhibitors (MIs), thereby abolishing infectivity. The CA (capsid) and SP1 (spacer peptide 1) region of Gag is the key regulator of assembly and maturation and is the target of MIs. We applied optimized cryo-electron tomography and subtomogram averaging to resolve this region within assembled immature HIV-1 particles at 3.9 angstrom resolution and built an atomic model. The structure reveals a network of intra- and intermolecular interactions mediating immature HIV-1 assembly. The proteolytic cleavage site between CA and SP1 is inaccessible to protease. We suggest that MIs prevent CA-SP1 cleavage by stabilizing the structure, and MI resistance develops by destabilizing CA-SP1.
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Affiliation(s)
- Florian K M Schur
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany. Molecular Medicine Partnership Unit, European Molecular Biology Laboratory-Universitätsklinikum Heidelberg, Heidelberg, Germany
| | - Martin Obr
- Molecular Medicine Partnership Unit, European Molecular Biology Laboratory-Universitätsklinikum Heidelberg, Heidelberg, Germany. Department of Infectious Diseases, Virology, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Wim J H Hagen
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - William Wan
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - Arjen J Jakobi
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany. Hamburg Unit c/o DESY (Deutsches Elektronen-Synchrotron), European Molecular Biology Laboratory, Notkestraße 85, 22607 Hamburg, Germany
| | - Joanna M Kirkpatrick
- Proteomics Core Facility, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - Carsten Sachse
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - Hans-Georg Kräusslich
- Molecular Medicine Partnership Unit, European Molecular Biology Laboratory-Universitätsklinikum Heidelberg, Heidelberg, Germany. Department of Infectious Diseases, Virology, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - John A G Briggs
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany. Molecular Medicine Partnership Unit, European Molecular Biology Laboratory-Universitätsklinikum Heidelberg, Heidelberg, Germany.
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28
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Helical arrays of U-shaped ATP synthase dimers form tubular cristae in ciliate mitochondria. Proc Natl Acad Sci U S A 2016; 113:8442-7. [PMID: 27402755 DOI: 10.1073/pnas.1525430113] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
F1Fo-ATP synthases are universal energy-converting membrane protein complexes that synthesize ATP from ADP and inorganic phosphate. In mitochondria of yeast and mammals, the ATP synthase forms V-shaped dimers, which assemble into rows along the highly curved ridges of lamellar cristae. Using electron cryotomography and subtomogram averaging, we have determined the in situ structure and organization of the mitochondrial ATP synthase dimer of the ciliate Paramecium tetraurelia. The ATP synthase forms U-shaped dimers with parallel monomers. Each complex has a prominent intracrista domain, which links the c-ring of one monomer to the peripheral stalk of the other. Close interaction of intracrista domains in adjacent dimers results in the formation of helical ATP synthase dimer arrays, which differ from the loose dimer rows in all other organisms observed so far. The parameters of the helical arrays match those of the cristae tubes, suggesting the unique features of the P. tetraurelia ATP synthase are directly responsible for generating the helical tubular cristae. We conclude that despite major structural differences between ATP synthase dimers of ciliates and other eukaryotes, the formation of ATP synthase dimer rows is a universal feature of mitochondria and a fundamental determinant of cristae morphology.
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29
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Kukulski W, Picco A, Specht T, Briggs JA, Kaksonen M. Clathrin modulates vesicle scission, but not invagination shape, in yeast endocytosis. eLife 2016; 5. [PMID: 27341079 PMCID: PMC4945154 DOI: 10.7554/elife.16036] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Accepted: 06/23/2016] [Indexed: 01/18/2023] Open
Abstract
In a previous paper (Picco et al., 2015), the dynamic architecture of the protein machinery during clathrin-mediated endocytosis was visualized using a new live imaging and particle tracking method. Here, by combining this approach with correlative light and electron microscopy, we address the role of clathrin in this process. During endocytosis, clathrin forms a cage-like coat around the membrane and associated protein components. There is growing evidence that clathrin does not determine the membrane morphology of the invagination but rather modulates the progression of endocytosis. We investigate how the deletion of clathrin heavy chain impairs the dynamics and the morphology of the endocytic membrane in budding yeast. Our results show that clathrin is not required for elongating or shaping the endocytic membrane invagination. Instead, we find that clathrin contributes to the regularity of vesicle scission and thereby to controlling vesicle size. DOI:http://dx.doi.org/10.7554/eLife.16036.001
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Affiliation(s)
- Wanda Kukulski
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Division of Cell Biology, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Andrea Picco
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Department of Biochemistry, University of Geneva, Geneva, Switzerland
| | - Tanja Specht
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - John Ag Briggs
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Marko Kaksonen
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Department of Biochemistry, University of Geneva, Geneva, Switzerland
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30
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Nucleic Acid Binding by Mason-Pfizer Monkey Virus CA Promotes Virus Assembly and Genome Packaging. J Virol 2016; 90:4593-4603. [PMID: 26912613 DOI: 10.1128/jvi.03197-15] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Accepted: 02/15/2016] [Indexed: 12/13/2022] Open
Abstract
UNLABELLED The Gag polyprotein of retroviruses drives immature virus assembly by forming hexameric protein lattices. The assembly is primarily mediated by protein-protein interactions between capsid (CA) domains and by interactions between nucleocapsid (NC) domains and RNA. Specific interactions between NC and the viral RNA are required for genome packaging. Previously reported cryoelectron microscopy analysis of immature Mason-Pfizer monkey virus (M-PMV) particles suggested that a basic region (residues RKK) in CA may serve as an additional binding site for nucleic acids. Here, we have introduced mutations into the RKK region in both bacterial and proviral M-PMV vectors and have assessed their impact on M-PMV assembly, structure, RNA binding, budding/release, nuclear trafficking, and infectivity using in vitro and in vivo systems. Our data indicate that the RKK region binds and structures nucleic acid that serves to promote virus particle assembly in the cytoplasm. Moreover, the RKK region appears to be important for recruitment of viral genomic RNA into Gag particles, and this function could be linked to changes in nuclear trafficking. Together these observations suggest that in M-PMV, direct interactions between CA and nucleic acid play important functions in the late stages of the viral life cycle. IMPORTANCE Assembly of retrovirus particles is driven by the Gag polyprotein, which can self-assemble to form virus particles and interact with RNA to recruit the viral genome into the particles. Generally, the capsid domains of Gag contribute to essential protein-protein interactions during assembly, while the nucleocapsid domain interacts with RNA. The interactions between the nucleocapsid domain and RNA are important both for identifying the genome and for self-assembly of Gag molecules. Here, we show that a region of basic residues in the capsid protein of the betaretrovirus Mason-Pfizer monkey virus (M-PMV) contributes to interaction of Gag with nucleic acid. This interaction appears to provide a critical scaffolding function that promotes assembly of virus particles in the cytoplasm. It is also crucial for packaging the viral genome and thus for infectivity. These data indicate that, surprisingly, interactions between the capsid domain and RNA play an important role in the assembly of M-PMV.
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31
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Structure of a bacterial type III secretion system in contact with a host membrane in situ. Nat Commun 2015; 6:10114. [PMID: 26656452 PMCID: PMC4682100 DOI: 10.1038/ncomms10114] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Accepted: 11/03/2015] [Indexed: 12/16/2022] Open
Abstract
Many bacterial pathogens of animals and plants use a conserved type III secretion system (T3SS) to inject virulence effector proteins directly into eukaryotic cells to subvert host functions. Contact with host membranes is critical for T3SS activation, yet little is known about T3SS architecture in this state or the conformational changes that drive effector translocation. Here we use cryo-electron tomography and sub-tomogram averaging to derive the intact structure of the primordial Chlamydia trachomatis T3SS in the presence and absence of host membrane contact. Comparison of the averaged structures demonstrates a marked compaction of the basal body (4 nm) occurs when the needle tip contacts the host cell membrane. This compaction is coupled to a stabilization of the cytosolic sorting platform–ATPase. Our findings reveal the first structure of a bacterial T3SS from a major human pathogen engaged with a eukaryotic host, and reveal striking ‘pump-action' conformational changes that underpin effector injection. Bacterial type III secretion systems (T3SSs) inject virulence effector proteins into eukaryotic cells and are activated by host membrane contact. Here the authors report the in situ structure of the Chlamydia trachomatis T3SS in the presence or absence of host membrane, and observe compaction of the basal body embedded in the bacterial envelope.
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32
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Three-Dimensional Structural Characterization of HIV-1 Tethered to Human Cells. J Virol 2015; 90:1507-21. [PMID: 26582000 DOI: 10.1128/jvi.01880-15] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Accepted: 11/14/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Tetherin (BST2, CD317, or HM1.24) is a host cellular restriction factor that prevents the release of enveloped viruses by mechanically linking virions to the plasma membrane. The precise arrangement of tetherin molecules at the plasma membrane site of HIV-1 assembly, budding, and restriction is not well understood. To gain insight into the biophysical mechanism underlying tetherin-mediated restriction of HIV-1, we utilized cryo-electron tomography (cryo-ET) to directly visualize HIV-1 virus-like particles (VLPs) and virions tethered to human cells in three dimensions (3D). Rod-like densities that we refer to as tethers were seen connecting HIV-1 virions to each other and to the plasma membrane. Native immunogold labeling showed tetherin molecules located on HIV-1 VLPs and virions in positions similar to those of the densities observed by cryo-ET. The location of the tethers with respect to the ordered immature Gag lattice or mature conical core was random. However, tethers were not uniformly distributed on the viral membrane but rather formed clusters at sites of contact with the cell or other virions. Chains of tethered HIV-1 virions often were arranged in a linear fashion, primarily as single chains and, to a lesser degree, as branched chains. Distance measurements support the extended tetherin model, in which the coiled-coil ectodomains are oriented perpendicular with respect to the viral and plasma membranes. IMPORTANCE Tetherin is a cellular factor that restricts HIV-1 release by directly cross-linking the virus to the host cell plasma membrane. We used cryo-electron tomography to visualize HIV-1 tethered to human cells in 3D. We determined that tetherin-restricted HIV-1 virions were physically connected to each other or to the plasma membrane by filamentous tethers that resembled rods ∼15 nm in length, which is consistent with the extended tetherin model. In addition, we found the position of the tethers to be arbitrary relative to the ordered immature Gag lattice or the mature conical cores. However, when present as multiple copies, the tethers clustered at the interface between virions. Tethered HIV-1 virions were arranged in a linear fashion, with the majority as single chains. This study advances our understanding of tetherin-mediated HIV-1 restriction by defining the spatial arrangement and orientation of tetherin molecules at sites of HIV-1 restriction.
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33
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Schur FKM, Dick RA, Hagen WJH, Vogt VM, Briggs JAG. The Structure of Immature Virus-Like Rous Sarcoma Virus Gag Particles Reveals a Structural Role for the p10 Domain in Assembly. J Virol 2015; 89:10294-302. [PMID: 26223638 PMCID: PMC4580193 DOI: 10.1128/jvi.01502-15] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 07/24/2015] [Indexed: 12/23/2022] Open
Abstract
UNLABELLED The polyprotein Gag is the primary structural component of retroviruses. Gag consists of independently folded domains connected by flexible linkers. Interactions between the conserved capsid (CA) domains of Gag mediate formation of hexameric protein lattices that drive assembly of immature virus particles. Proteolytic cleavage of Gag by the viral protease (PR) is required for maturation of retroviruses from an immature form into an infectious form. Within the assembled Gag lattices of HIV-1 and Mason-Pfizer monkey virus (M-PMV), the C-terminal domain of CA adopts similar quaternary arrangements, while the N-terminal domain of CA is packed in very different manners. Here, we have used cryo-electron tomography and subtomogram averaging to study in vitro-assembled, immature virus-like Rous sarcoma virus (RSV) Gag particles and have determined the structure of CA and the surrounding regions to a resolution of ∼8 Å. We found that the C-terminal domain of RSV CA is arranged similarly to HIV-1 and M-PMV, whereas the N-terminal domain of CA adopts a novel arrangement in which the upstream p10 domain folds back into the CA lattice. In this position the cleavage site between CA and p10 appears to be inaccessible to PR. Below CA, an extended density is consistent with the presence of a six-helix bundle formed by the spacer-peptide region. We have also assessed the affect of lattice assembly on proteolytic processing by exogenous PR. The cleavage between p10 and CA is indeed inhibited in the assembled lattice, a finding consistent with structural regulation of proteolytic maturation. IMPORTANCE Retroviruses first assemble into immature virus particles, requiring interactions between Gag proteins that form a protein layer under the viral membrane. Subsequently, Gag is cleaved by the viral protease enzyme into separate domains, leading to rearrangement of the virus into its infectious form. It is important to understand how Gag is arranged within immature retroviruses, in order to understand how virus assembly occurs, and how maturation takes place. We used the techniques cryo-electron tomography and subtomogram averaging to obtain a detailed structural picture of the CA domains in immature assembled Rous sarcoma virus Gag particles. We found that part of Gag next to CA, called p10, folds back and interacts with CA when Gag assembles. This arrangement is different from that seen in HIV-1 and Mason-Pfizer monkey virus, illustrating further structural diversity of retroviral structures. The structure provides new information on how the virus assembles and undergoes maturation.
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Affiliation(s)
- Florian K M Schur
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany Molecular Medicine Partnership Unit, Heidelberg, Germany
| | - Robert A Dick
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, USA
| | - Wim J H Hagen
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Volker M Vogt
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, USA
| | - John A G Briggs
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany Molecular Medicine Partnership Unit, Heidelberg, Germany
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34
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Darrow MC, Sergeeva OA, Isas JM, Galaz-Montoya JG, King JA, Langen R, Schmid MF, Chiu W. Structural Mechanisms of Mutant Huntingtin Aggregation Suppression by the Synthetic Chaperonin-like CCT5 Complex Explained by Cryoelectron Tomography. J Biol Chem 2015; 290:17451-61. [PMID: 25995452 DOI: 10.1074/jbc.m115.655373] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Indexed: 11/06/2022] Open
Abstract
Huntington disease, a neurodegenerative disorder characterized by functional deficits and loss of striatal neurons, is linked to an expanded and unstable CAG trinucleotide repeat in the huntingtin gene (HTT). This DNA sequence translates to a polyglutamine repeat in the protein product, leading to mutant huntingtin (mHTT) protein aggregation. The aggregation of mHTT is inhibited in vitro and in vivo by the TCP-1 ring complex (TRiC) chaperonin. Recently, a novel complex comprised of a single type of TRiC subunit has been reported to inhibit mHTT aggregation. Specifically, the purified CCT5 homo-oligomer complex, when compared with TRiC, has a similar structure, ATP use, and substrate refolding activity, and, importantly, it also inhibits mHTT aggregation. Using an aggregation suppression assay and cryoelectron tomography coupled with a novel computational classification method, we uncover the interactions between the synthetic CCT5 complex (∼ 1 MDa) and aggregates of mutant huntingtin exon 1 containing 46 glutamines (mHTTQ46-Ex1). We find that, in a similar fashion to TRiC, synthetic CCT5 complex caps mHTT fibrils at their tips and encapsulates mHTT oligomers, providing a structural description of the inhibition of mHTTQ46-Ex1 by CCT5 complex and a shared mechanism of mHTT inhibition between TRiC chaperonin and the CCT5 complex: cap and contain.
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Affiliation(s)
- Michele C Darrow
- From the National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030
| | - Oksana A Sergeeva
- the Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and
| | - Jose M Isas
- the Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Jesús G Galaz-Montoya
- From the National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030
| | - Jonathan A King
- the Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and
| | - Ralf Langen
- the Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
| | - Michael F Schmid
- From the National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030
| | - Wah Chiu
- From the National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030,
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35
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Jiko C, Davies KM, Shinzawa-Itoh K, Tani K, Maeda S, Mills DJ, Tsukihara T, Fujiyoshi Y, Kühlbrandt W, Gerle C. Bovine F1Fo ATP synthase monomers bend the lipid bilayer in 2D membrane crystals. eLife 2015; 4:e06119. [PMID: 25815585 PMCID: PMC4413875 DOI: 10.7554/elife.06119] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 03/26/2015] [Indexed: 01/06/2023] Open
Abstract
We have used a combination of electron cryo-tomography, subtomogram averaging, and electron crystallographic image processing to analyse the structure of intact bovine F1Fo ATP synthase in 2D membrane crystals. ATPase assays and mass spectrometry analysis of the 2D crystals confirmed that the enzyme complex was complete and active. The structure of the matrix-exposed region was determined at 24 Å resolution by subtomogram averaging and repositioned into the tomographic volume to reveal the crystal packing. F1Fo ATP synthase complexes are inclined by 16° relative to the crystal plane, resulting in a zigzag topology of the membrane and indicating that monomeric bovine heart F1Fo ATP synthase by itself is sufficient to deform lipid bilayers. This local membrane curvature is likely to be instrumental in the formation of ATP synthase dimers and dimer rows, and thus for the shaping of mitochondrial cristae. DOI:http://dx.doi.org/10.7554/eLife.06119.001 Cells use a molecule called adenosine triphosphate (or ATP for short) to power many processes that are vital for life. Animals, plants, and fungi primarily make their ATP in a specialised compartment called the mitochondrion, which is found inside their cells. The mitochondrion is often referred to as the powerhouse of cells as it captures and stores the energy that animals gain from eating food in the molecule ATP. Other enzymes in the cell break apart ATP to release the stored energy, which they use to power various cellular processes. The interior architecture of the mitochondrion includes a highly folded inner membrane where electrical energy is transformed into chemical energy. The tight folding of the inner membrane is thought to make this process more efficient. An enzyme named ATP synthase performs the final steps of the energy transformation process by producing ATP (ATP synthase literally means ‘ATP maker’). This enzyme sits in pairs along the edges of the inner membrane folds. This raises the question: does the ATP synthase cause the membrane to fold or does this enzyme just ‘prefer’ these folded edges (which are instead caused by something else inside the mitochondrion)? To investigate this question, Jiko, Davies et al. extracted ATP synthase from the mitochondria of cow hearts and mixed them with modified fat molecules to form a ‘2D membrane crystal’: a membrane containing an ordered pattern of enzymes. An electron microscope was used to generate a three-dimensional volume of the 2D membrane crystal via a process similar to a MRI or CAT scan that one might have in hospital. In the three-dimensional volume of the membrane crystal, Jiko, Davies et al. discovered that instead of being flat as expected, the membrane of the 2D membrane crystal was rippled and that this ripple was caused by the membrane-embedded part of the ATP synthase. The geometry of the ripple exactly matched half of the bend at the edge of the membrane folds in the mitochondrion. Therefore, Jiko, Davies et al. concluded that a pair of ATP synthases, as found in mitochondria, was responsible for defining the tight folds of the inner mitochondrial membrane. DOI:http://dx.doi.org/10.7554/eLife.06119.002
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Affiliation(s)
- Chimari Jiko
- Institute for Protein Research, Osaka University, Osaka, Japan
| | - Karen M Davies
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Kyoko Shinzawa-Itoh
- Picobiology Institute, Department of Life Science, Graduate School of Life Science, University of Hyogo, Kamigori, Japan
| | - Kazutoshi Tani
- Cellular and Structural Physiology Institute, Nagoya University, Nagoya, Japan
| | - Shintaro Maeda
- Picobiology Institute, Department of Life Science, Graduate School of Life Science, University of Hyogo, Kamigori, Japan
| | - Deryck J Mills
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Tomitake Tsukihara
- Picobiology Institute, Department of Life Science, Graduate School of Life Science, University of Hyogo, Kamigori, Japan
| | - Yoshinori Fujiyoshi
- Cellular and Structural Physiology Institute, Nagoya University, Nagoya, Japan
| | - Werner Kühlbrandt
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Christoph Gerle
- Picobiology Institute, Department of Life Science, Graduate School of Life Science, University of Hyogo, Kamigori, Japan
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Schur FKM, Hagen WJH, Rumlová M, Ruml T, Müller B, Kräusslich HG, Briggs JAG. Structure of the immature HIV-1 capsid in intact virus particles at 8.8 Å resolution. Nature 2014; 517:505-8. [PMID: 25363765 DOI: 10.1038/nature13838] [Citation(s) in RCA: 229] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2014] [Accepted: 09/03/2014] [Indexed: 12/16/2022]
Abstract
Human immunodeficiency virus type 1 (HIV-1) assembly proceeds in two stages. First, the 55 kilodalton viral Gag polyprotein assembles into a hexameric protein lattice at the plasma membrane of the infected cell, inducing budding and release of an immature particle. Second, Gag is cleaved by the viral protease, leading to internal rearrangement of the virus into the mature, infectious form. Immature and mature HIV-1 particles are heterogeneous in size and morphology, preventing high-resolution analysis of their protein arrangement in situ by conventional structural biology methods. Here we apply cryo-electron tomography and sub-tomogram averaging methods to resolve the structure of the capsid lattice within intact immature HIV-1 particles at subnanometre resolution, allowing unambiguous positioning of all α-helices. The resulting model reveals tertiary and quaternary structural interactions that mediate HIV-1 assembly. Strikingly, these interactions differ from those predicted by the current model based on in vitro-assembled arrays of Gag-derived proteins from Mason-Pfizer monkey virus. To validate this difference, we solve the structure of the capsid lattice within intact immature Mason-Pfizer monkey virus particles. Comparison with the immature HIV-1 structure reveals that retroviral capsid proteins, while having conserved tertiary structures, adopt different quaternary arrangements during virus assembly. The approach demonstrated here should be applicable to determine structures of other proteins at subnanometre resolution within heterogeneous environments.
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Affiliation(s)
- Florian K M Schur
- 1] Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany [2] Molecular Medicine Partnership Unit, European Molecular Biology Laboratory/Universitätsklinikum Heidelberg, Heidelberg, Germany
| | - Wim J H Hagen
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Michaela Rumlová
- 1] Institute of Organic Chemistry and Biochemistry (IOCB), Academy of Sciences of the Czech Republic, v.v.i., IOCB &Gilead Research Center, Flemingovo nám. 2, 166 10 Prague, Czech Republic [2] Department of Biotechnology, Institute of Chemical Technology, Prague, Technická 5, 166 28, Prague, Czech Republic
| | - Tomáš Ruml
- Department of Biochemistry and Microbiology, Institute of Chemical Technology, Prague, Technická 5, 166 28, Prague, Czech Republic
| | - Barbara Müller
- 1] Molecular Medicine Partnership Unit, European Molecular Biology Laboratory/Universitätsklinikum Heidelberg, Heidelberg, Germany [2] Department of Infectious Diseases, Virology, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Hans-Georg Kräusslich
- 1] Molecular Medicine Partnership Unit, European Molecular Biology Laboratory/Universitätsklinikum Heidelberg, Heidelberg, Germany [2] Department of Infectious Diseases, Virology, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - John A G Briggs
- 1] Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany [2] Molecular Medicine Partnership Unit, European Molecular Biology Laboratory/Universitätsklinikum Heidelberg, Heidelberg, Germany
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Davies KM, Daum B, Gold VAM, Mühleip AW, Brandt T, Blum TB, Mills DJ, Kühlbrandt W. Visualization of ATP synthase dimers in mitochondria by electron cryo-tomography. J Vis Exp 2014:51228. [PMID: 25285856 PMCID: PMC4828066 DOI: 10.3791/51228] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Electron cryo-tomography is a powerful tool in structural biology, capable of visualizing the three-dimensional structure of biological samples, such as cells, organelles, membrane vesicles, or viruses at molecular detail. To achieve this, the aqueous sample is rapidly vitrified in liquid ethane, which preserves it in a close-to-native, frozen-hydrated state. In the electron microscope, tilt series are recorded at liquid nitrogen temperature, from which 3D tomograms are reconstructed. The signal-to-noise ratio of the tomographic volume is inherently low. Recognizable, recurring features are enhanced by subtomogram averaging, by which individual subvolumes are cut out, aligned and averaged to reduce noise. In this way, 3D maps with a resolution of 2 nm or better can be obtained. A fit of available high-resolution structures to the 3D volume then produces atomic models of protein complexes in their native environment. Here we show how we use electron cryo-tomography to study the in situ organization of large membrane protein complexes in mitochondria. We find that ATP synthases are organized in rows of dimers along highly curved apices of the inner membrane cristae, whereas complex I is randomly distributed in the membrane regions on either side of the rows. By subtomogram averaging we obtained a structure of the mitochondrial ATP synthase dimer within the cristae membrane.
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Affiliation(s)
- Karen M Davies
- Department of Structural Biology, Max Planck Institute of Biophysics
| | - Bertram Daum
- Department of Structural Biology, Max Planck Institute of Biophysics
| | - Vicki A M Gold
- Department of Structural Biology, Max Planck Institute of Biophysics
| | | | - Tobias Brandt
- Department of Structural Biology, Max Planck Institute of Biophysics
| | - Thorsten B Blum
- Department of Structural Biology, Max Planck Institute of Biophysics
| | - Deryck J Mills
- Department of Structural Biology, Max Planck Institute of Biophysics
| | - Werner Kühlbrandt
- Department of Structural Biology, Max Planck Institute of Biophysics;
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38
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Nans A, Saibil HR, Hayward RD. Pathogen-host reorganization during Chlamydia invasion revealed by cryo-electron tomography. Cell Microbiol 2014; 16:1457-72. [PMID: 24809274 PMCID: PMC4336559 DOI: 10.1111/cmi.12310] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Revised: 05/01/2014] [Accepted: 05/02/2014] [Indexed: 02/06/2023]
Abstract
Invasion of host cells is a key early event during bacterial infection, but the underlying pathogen–host interactions are yet to be fully visualized in three-dimensional detail. We have captured snapshots of the early stages of bacterial-mediated endocytosis in situ by exploiting the small size of chlamydial elementary bodies (EBs) for whole-cell cryo-electron tomography. Chlamydiae are obligate intracellular bacteria that infect eukaryotic cells and cause sexually transmitted infections and trachoma, the leading cause of preventable blindness. We demonstrate that Chlamydia trachomatis LGV2 EBs are intrinsically polarized. One pole is characterized by a tubular inner membrane invagination, while the other exhibits asymmetric periplasmic expansion to accommodate an array of type III secretion systems (T3SSs). Strikingly, EBs orient with their T3SS-containing pole facing target cells, enabling the T3SSs to directly contact the cellular plasma membrane. This contact induces enveloping macropinosomes, actin-rich filopodia and phagocytic cups to zipper tightly around the internalizing bacteria. Once encapsulated into tight early vacuoles, EB polarity and the T3SSs are lost. Our findings reveal previously undescribed structural transitions in both pathogen and host during the initial steps of chlamydial invasion.
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Affiliation(s)
- Andrea Nans
- Department of Crystallography, Institute of Structural and Molecular Biology, Birkbeck College, University of London, Malet Street, London, WC1E 7HX, UK
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Yu Z, Frangakis AS. M-free: scoring the reference bias in sub-tomogram averaging and template matching. J Struct Biol 2014; 187:10-19. [PMID: 24859794 DOI: 10.1016/j.jsb.2014.05.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Revised: 04/23/2014] [Accepted: 05/15/2014] [Indexed: 11/27/2022]
Abstract
Cryo-electron tomography provides a snapshot of the cellular proteome. With template matching, the spatial positions of various macromolecular complexes within their native cellular context can be detected. However, the growing awareness of the reference bias introduced by the cross-correlation based approaches, and more importantly the lack of a reliable confidence measurement in the selection of these macromolecular complexes, has restricted the use of these applications. Here we propose a heuristic, in which the reference bias is measured in real space in an analogous way to the R-free value in X-ray crystallography. We measure the reference bias within the mask used to outline the area of the template, and do not modify the template itself. The heuristic works by splitting the mask into a working and a testing area in a volume ratio of 9:1. While the working area is used during the calculation of the cross-correlation function, the information from both areas is explored to calculate the M-free score. We show using artificial data, that the M-free score gives a reliable measure for the reference bias. The heuristic can be applied in template matching and in sub-tomogram averaging. We further test the applicability of the heuristic in tomograms of purified macromolecules, and tomograms of whole Mycoplasma cells.
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Affiliation(s)
- Zhou Yu
- Goethe University Frankfurt, Buchmann Institute for Molecular Life Sciences and Institute for Biophysics, Max-von-Laue Str.15, 60438 Frankfurt am Main, Germany
| | - Achilleas S Frangakis
- Goethe University Frankfurt, Buchmann Institute for Molecular Life Sciences and Institute for Biophysics, Max-von-Laue Str.15, 60438 Frankfurt am Main, Germany.
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40
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Geiss CP, Keramisanou D, Sekulic N, Scheffer MP, Black BE, Frangakis AS. CENP-A arrays are more condensed than canonical arrays at low ionic strength. Biophys J 2014; 106:875-82. [PMID: 24559990 PMCID: PMC3944588 DOI: 10.1016/j.bpj.2014.01.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Revised: 01/02/2014] [Accepted: 01/07/2014] [Indexed: 10/25/2022] Open
Abstract
The centromeric histone H3 variant centromeric protein A (CENP-A), whose sequence is the least conserved among all histone variants, is responsible for specifying the location of the centromere. Here, we present a comprehensive study of CENP-A nucleosome arrays by cryo-electron tomography. We see that CENP-A arrays have different biophysical properties than canonical ones under low ionic conditions, as they are more condensed with a 20% smaller average nearest-neighbor distance and a 30% higher nucleosome density. We find that CENP-A nucleosomes have a predominantly crossed DNA entry/exit site that is narrowed on average by 8°, and they have a propensity to stack face to face. We therefore propose that CENP-A induces geometric constraints at the nucleosome DNA entry/exit site to bring neighboring nucleosomes into close proximity. This specific property of CENP-A may be responsible for generating a fundamental process that contributes to increased chromatin fiber compaction that is propagated under physiological conditions to form centromeric chromatin.
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Affiliation(s)
| | | | - Nikolina Sekulic
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | | | - Ben E Black
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
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41
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Determination of protein structure at 8.5Å resolution using cryo-electron tomography and sub-tomogram averaging. J Struct Biol 2013; 184:394-400. [DOI: 10.1016/j.jsb.2013.10.015] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Revised: 10/18/2013] [Accepted: 10/19/2013] [Indexed: 11/19/2022]
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42
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Davis NJ, Cohen Y, Sanselicio S, Fumeaux C, Ozaki S, Luciano J, Guerrero-Ferreira RC, Wright ER, Jenal U, Viollier PH. De- and repolarization mechanism of flagellar morphogenesis during a bacterial cell cycle. Genes Dev 2013; 27:2049-62. [PMID: 24065770 PMCID: PMC3792480 DOI: 10.1101/gad.222679.113] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Eukaryotic morphogenesis is seeded with the establishment and subsequent amplification of polarity cues at key times during the cell cycle, often using (cyclic) nucleotide signals. We discovered that flagellum de- and repolarization in the model prokaryote Caulobacter crescentus is precisely orchestrated through at least three spatiotemporal mechanisms integrated at TipF. We show that TipF is a cell cycle-regulated receptor for the second messenger--bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP)--that perceives and transduces this signal through the degenerate c-di-GMP phosphodiesterase (EAL) domain to nucleate polar flagellum biogenesis. Once c-di-GMP levels rise at the G1 → S transition, TipF is activated, stabilized, and polarized, enabling the recruitment of downstream effectors, including flagellar switch proteins and the PflI positioning factor, at a preselected pole harboring the TipN landmark. These c-di-GMP-dependent events are coordinated with the onset of tipF transcription in early S phase and together enable the correct establishment and robust amplification of TipF-dependent polarization early in the cell cycle. Importantly, these mechanisms also govern the timely removal of TipF at cell division coincident with the drop in c-di-GMP levels, thereby resetting the flagellar polarization state in the next cell cycle after a preprogrammed period during which motility must be suspended.
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Affiliation(s)
- Nicole J Davis
- Department of Molecular Biology and Microbiology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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43
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Al-Amoudi A, Frangakis AS. Three-dimensional visualization of the molecular architecture of cell-cell junctions in situ by cryo-electron tomography of vitreous sections. Methods Mol Biol 2013; 961:97-117. [PMID: 23325637 DOI: 10.1007/978-1-62703-227-8_4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Cryo-electron tomography of vitreous sections is currently the only method for visualizing the eukaryotic ultrastructure at close to native state with molecular resolution. Here, we describe the detailed procedure of how to prepare suitable vitreous sections from mammalian skin for cryo-electron tomography, how to align the projection images of the tilt-series, and finally how to perform sub-tomogram averaging on macromolecular complexes with periodic arrangement such as desmosomes.
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Affiliation(s)
- Ashraf Al-Amoudi
- Deutsches Zentrum für Neurodegenerative Erkrankungen e.V, Bonn, Germany.
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44
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Plasma membrane reshaping during endocytosis is revealed by time-resolved electron tomography. Cell 2012; 150:508-20. [PMID: 22863005 DOI: 10.1016/j.cell.2012.05.046] [Citation(s) in RCA: 246] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Revised: 04/04/2012] [Accepted: 05/17/2012] [Indexed: 12/22/2022]
Abstract
Endocytosis, like many dynamic cellular processes, requires precise temporal and spatial orchestration of complex protein machinery to mediate membrane budding. To understand how this machinery works, we directly correlated fluorescence microscopy of key protein pairs with electron tomography. We systematically located 211 endocytic intermediates, assigned each to a specific time window in endocytosis, and reconstructed their ultrastructure in 3D. The resulting virtual ultrastructural movie defines the protein-mediated membrane shape changes during endocytosis in budding yeast. It reveals that clathrin is recruited to flat membranes and does not initiate curvature. Instead, membrane invagination begins upon actin network assembly followed by amphiphysin binding to parallel membrane segments, which promotes elongation of the invagination into a tubule. Scission occurs on average 9 s after initial bending when invaginations are ∼100 nm deep, releasing nonspherical vesicles with 6,400 nm2 mean surface area. Direct correlation of protein dynamics with ultrastructure provides a quantitative 4D resource.
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45
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Fernandez JJ. Computational methods for electron tomography. Micron 2012; 43:1010-30. [DOI: 10.1016/j.micron.2012.05.003] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Revised: 05/08/2012] [Accepted: 05/08/2012] [Indexed: 01/13/2023]
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46
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Structure of the yeast F1Fo-ATP synthase dimer and its role in shaping the mitochondrial cristae. Proc Natl Acad Sci U S A 2012; 109:13602-7. [PMID: 22864911 DOI: 10.1073/pnas.1204593109] [Citation(s) in RCA: 352] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
We used electron cryotomography of mitochondrial membranes from wild-type and mutant Saccharomyces cerevisiae to investigate the structure and organization of ATP synthase dimers in situ. Subtomogram averaging of the dimers to 3.7 nm resolution revealed a V-shaped structure of twofold symmetry, with an angle of 86° between monomers. The central and peripheral stalks are well resolved. The monomers interact within the membrane at the base of the peripheral stalks. In wild-type mitochondria ATP synthase dimers are found in rows along the highly curved cristae ridges, and appear to be crucial for membrane morphology. Strains deficient in the dimer-specific subunits e and g or the first transmembrane helix of subunit 4 lack both dimers and lamellar cristae. Instead, cristae are either absent or balloon-shaped, with ATP synthase monomers distributed randomly in the membrane. Computer simulations indicate that isolated dimers induce a plastic deformation in the lipid bilayer, which is partially relieved by their side-by-side association. We propose that the assembly of ATP synthase dimer rows is driven by the reduction in the membrane elastic energy, rather than by direct protein contacts, and that the dimer rows enable the formation of highly curved ridges in mitochondrial cristae.
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47
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MORALES JUAN, ALONSO-NANCLARES LIDIA, RODRÍGUEZ JOSÉRODRIGO, MERCHÁN-PÉREZ ÁNGEL, DEFELIPE JAVIER, RODRÍGUEZ ÁNGEL. FAST INTERACTIVE QUANTIFICATION OF SYNAPSES IN THE CEREBRAL CORTEX. INT J ARTIF INTELL T 2012. [DOI: 10.1142/s0218213011000139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Synapses are key elements in the organization of neuronal circuits. To analyse these structures, it is now possible to obtain serial images from large samples of nervous tissue in an automated manner through combined focused ion beam milling and scanning electron microscopy. However, the identification, 3D reconstruction and quantification of synapses within these samples are labor intensive procedures that require continuous user intervention. We have developed a software tool to achieve the segmentation of synapses in a reconstructed 3D volume of the cerebral cortex, thereby greatly facilitating and accelerating these processes. The tool is interactive, allowing the user to supervise the segmentation process, to modify the appropriate parameters and to validate the results. Some experimental results obtained with our tool in the rat cerebral cortex are also presented.
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Affiliation(s)
- JUAN MORALES
- CesViMa, Universidad Politécnica de Madrid (UPM), Campus de Montegancedo s/n Pozuelo de Alarcón, 28223 Madrid, Spain
| | - LIDIA ALONSO-NANCLARES
- Laboratorio Cajal de Circuitos, Centro de Tecnología Biomédica, Universidad Politécnica de Madrid (UPM) and Instituto Cajal, CSIC, Campus de Montegancedo s/n Pozuelo de Alarcón, 28223 Madrid, Spain
| | - JOSÉ-RODRIGO RODRÍGUEZ
- Laboratorio Cajal de Circuitos, Centro de Tecnología Biomédica, Universidad Politécnica de Madrid (UPM) and Instituto Cajal, CSIC, Campus de Montegancedo s/n Pozuelo de Alarcón, 28223 Madrid, Spain
| | - ÁNGEL MERCHÁN-PÉREZ
- Laboratorio Cajal de Circuitos, Centro de Tecnología Biomédica and Departamento de Arquitectura y Tecnología de Sistemas Informáticos, Universidad Politécnica de Madrid (UPM), Campus de Montegancedo s/n Pozuelo de Alarcón, 28223 Madrid, Spain
| | - JAVIER DEFELIPE
- Laboratorio Cajal de Circuitos, Centro de Tecnología Biomédica, Universidad Politécnica de Madrid (UPM) and Instituto Cajal, CSIC, Campus de Montegancedo s/n Pozuelo de Alarcón, 28223 Madrid, Spain
| | - ÁNGEL RODRÍGUEZ
- Departamento de Tecnología Fotónica, Universidad Politécnica de Madrid (UPM), Campus de Montegancedo s/n Boadilla del Monte, 28660 Madrid, Spain
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48
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Scheffer MP, Eltsov M, Bednar J, Frangakis AS. Nucleosomes stacked with aligned dyad axes are found in native compact chromatin in vitro. J Struct Biol 2011; 178:207-14. [PMID: 22138167 DOI: 10.1016/j.jsb.2011.11.020] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Revised: 11/10/2011] [Accepted: 11/15/2011] [Indexed: 11/28/2022]
Abstract
In this study, electron tomograms of plunge-frozen isolated chromatin in both open and compacted form were recorded. We have resolved individual nucleosomes in these tomograms in order to provide a 3D view of the arrangement of nucleosomes within chromatin fibers at different compaction states. With an optimized template matching procedure we obtained accurate positions and orientations of nucleosomes in open chromatin in "low-salt" conditions (5 mM NaCl). The mean value of the planar angle between three consecutive nucleosomes is 70°, and the mean center-to-center distance between consecutive nucleosomes is 22.3 nm. Since the template matching approach was not effective in crowded conditions, for nucleosome detection in compact fibers (40 mM NaCl and 1 mM MgCl(2)) we developed the nucleosome detection procedure based on the watershed algorithm, followed by sub-tomogram alignment, averaging, and classification by Principal Components Analysis. We find that in compact chromatin the nucleosomes are arranged with a predominant face-to-face stacking organization, which has not been previously shown for native isolated chromatin. Although the path of the DNA cannot be directly seen in compact conditions, it is evident that the nucleosomes stack with their dyad axis aligned in forming a "double track" conformation which is a consequence of DNA joining adjacent nucleosome stacks. Our data suggests that nucleosome stacking is an important mechanism for generating chromatin compaction in vivo.
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Affiliation(s)
- Margot P Scheffer
- European Molecular Biology Laboratory, Meyerhofstr. 1, 69117 Heidelberg, Germany.
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49
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Evidence for short-range helical order in the 30-nm chromatin fibers of erythrocyte nuclei. Proc Natl Acad Sci U S A 2011; 108:16992-7. [PMID: 21969536 DOI: 10.1073/pnas.1108268108] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Chromatin folding in eukaryotes fits the genome into the limited volume of the cell nucleus. Formation of higher-order chromatin structures attenuates DNA accessibility, thus contributing to the control of essential genome functions such as transcription, DNA replication, and repair. The 30-nm fiber is thought to be the first hierarchical level of chromatin folding, but the nucleosome arrangement in the compact 30-nm fiber was previously unknown. We used cryoelectron tomography of vitreous sections to determine the structure of the compact, native 30-nm fiber of avian erythrocyte nuclei. The predominant geometry of the 30-nm fiber revealed by subtomogram averaging is a left-handed two-start helix with approximately 6.5 nucleosomes per 11 nm, in which the nucleosomes are juxtaposed face-to-face but are shifted off their superhelical axes with an axial translation of approximately 3.4 nm and an azimuthal rotation of approximately 54°. The nucleosomes produce a checkerboard pattern when observed in the direction perpendicular to the fiber axis but are not interdigitated. The nucleosome packing within the fibers shows larger center-to-center internucleosomal distances than previously anticipated, thus excluding the possibility of core-to-core interactions, explaining how transcription and regulation factors can access nucleosomes.
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50
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Edged watershed segmentation: a semi-interactive algorithm for segmentation of low-resolution maps from electron cryomicroscopy. J Struct Biol 2011; 176:127-32. [PMID: 21763426 DOI: 10.1016/j.jsb.2011.06.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Revised: 06/15/2011] [Accepted: 06/29/2011] [Indexed: 11/23/2022]
Abstract
Electron cryomicroscopy (cryo-EM) allows for the structural analysis of large protein complexes that may be difficult to study by other means. Frequently, maps of complexes from cryo-EM are obtained at resolutions between 10 and 25Å. To aid in the interpretation of these medium- to low-resolution maps, they may be subdivided into three-dimensional segments representing subunits or subcomplexes. This division is often accomplished using a manual segmentation approach. While extremely useful, manual segmentation is subjective. We have developed a novel semi-interactive segmentation algorithm that can incorporate prior knowledge of subunit composition or structure without biasing the boundaries between subunits or subcomplexes. This algorithm has been characterized with experimental and simulated cryo-EM density maps at resolutions between 10 and 25Å.
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