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A novel capsid protein network allows the characteristic internal membrane structure of Marseilleviridae giant viruses. Sci Rep 2022; 12:21428. [PMID: 36504202 PMCID: PMC9742146 DOI: 10.1038/s41598-022-24651-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2022] [Accepted: 11/18/2022] [Indexed: 12/14/2022] Open
Abstract
Marseilleviridae is a family of giant viruses, showing a characteristic internal membrane with extrusions underneath the icosahedral vertices. However, such large objects, with a maximum diameter of 250 nm are technically difficult to examine at sub-nanometre resolution by cryo-electron microscopy. Here, we tested the utility of 1 MV high-voltage cryo-EM (cryo-HVEM) for single particle structural analysis (SPA) of giant viruses using tokyovirus, a species of Marseilleviridae, and revealed the capsid structure at 7.7 Å resolution. The capsid enclosing the viral DNA consisted primarily of four layers: (1) major capsid proteins (MCPs) and penton proteins, (2) minor capsid proteins (mCPs), (3) scaffold protein components (ScPCs), and (4) internal membrane. The mCPs showed a novel capsid lattice consisting of eight protein components. ScPCs connecting the icosahedral vertices supported the formation of the membrane extrusions, and possibly act like tape measure proteins reported in other giant viruses. The density on top of the MCP trimer was suggested to include glycoproteins. This is the first attempt at cryo-HVEM SPA. We found the primary limitations to be the lack of automated data acquisition and software support for collection and processing and thus achievable resolution. However, the results pave the way for using cryo-HVEM for structural analysis of larger biological specimens.
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Burton-Smith RN, Murata K. Cryo-Electron Microscopy of the Giant Viruses. Microscopy (Oxf) 2021; 70:477-486. [PMID: 34490462 DOI: 10.1093/jmicro/dfab036] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Revised: 08/26/2021] [Accepted: 08/30/2021] [Indexed: 11/12/2022] Open
Abstract
High resolution study of the giant viruses presents one of the latest challenges in cryo-electron microscopy of viruses. Too small for light microscopy, but too large for easy study at high resolution by electron microscopy, they range in size from ~0.2-2 μm, from high symmetry icosahedral viruses such as Paramecium burseria Chlorella virus 1 to asymmetric forms like Tupanvirus or Pithovirus. To attain high resolution, two strategies exist to study these large viruses by cryo-EM: firstly, increasing the acceleration voltage of the electron microscope to improve sample penetration and overcome the limitations imposed by electro-optical physics at lower voltages, and secondly the method of "block-based reconstruction" pioneered by Michael G. Rossmann and his collaborators, which resolves the latter limitation through an elegant leveraging of high symmetry, but cannot overcome sample penetration limitations. In addition, more recent advances in both computational capacity and image processing also yield assistance in studying the giant viruses. Especially, the inclusion of Ewald sphere correction can provide large improvements in attainable resolutions for 300 kV electron microscopes. Despite this, the study of giant viruses remains a significant challenge.
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Affiliation(s)
- Raymond N Burton-Smith
- Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi, Japan.,National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Aichi, Japan
| | - Kazuyoshi Murata
- Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi, Japan.,National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Aichi, Japan.,Department of Physiological Sciences, School of Life Science, The Graduate University for Advanced Studies (SOKENDAI), Okazaki, Aichi, Japan
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Sahmi-Bounsiar D, Rolland C, Aherfi S, Boudjemaa H, Levasseur A, La Scola B, Colson P. Marseilleviruses: An Update in 2021. Front Microbiol 2021; 12:648731. [PMID: 34149639 PMCID: PMC8208085 DOI: 10.3389/fmicb.2021.648731] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2021] [Accepted: 04/12/2021] [Indexed: 01/19/2023] Open
Abstract
The family Marseilleviridae was the second family of giant viruses that was described in 2013, after the family Mimiviridae. Marseillevirus marseillevirus, isolated in 2007 by coculture on Acanthamoeba polyphaga, is the prototype member of this family. Afterward, the worldwide distribution of marseilleviruses was revealed through their isolation from samples of various types and sources. Thus, 62 were isolated from environmental water, one from soil, one from a dipteran, one from mussels, and two from asymptomatic humans, which led to the description of 67 marseillevirus isolates, including 21 by the IHU Méditerranée Infection in France. Recently, five marseillevirus genomes were assembled from deep sea sediment in Norway. Isolated marseilleviruses have ≈250 nm long icosahedral capsids and 348–404 kilobase long mosaic genomes that encode 386–545 predicted proteins. Comparative genomic analyses indicate that the family Marseilleviridae includes five lineages and possesses a pangenome composed of 3,082 clusters of genes. The detection of marseilleviruses in both symptomatic and asymptomatic humans in stool, blood, and lymph nodes, and an up-to-30-day persistence of marseillevirus in rats and mice, raise questions concerning their possible clinical significance that are still under investigation.
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Affiliation(s)
- Dehia Sahmi-Bounsiar
- IHU Méditerranée Infection, Marseille, France.,Institut de Recherche pour le Développement (IRD), Assistance Publique- Hôpitaux de Marseille (AP-HM), MEPHI, Aix-Marseille Université, Marseille, France
| | - Clara Rolland
- IHU Méditerranée Infection, Marseille, France.,Institut de Recherche pour le Développement (IRD), Assistance Publique- Hôpitaux de Marseille (AP-HM), MEPHI, Aix-Marseille Université, Marseille, France
| | - Sarah Aherfi
- IHU Méditerranée Infection, Marseille, France.,Institut de Recherche pour le Développement (IRD), Assistance Publique- Hôpitaux de Marseille (AP-HM), MEPHI, Aix-Marseille Université, Marseille, France
| | - Hadjer Boudjemaa
- IHU Méditerranée Infection, Marseille, France.,Department of Biology, Faculty of Natural Science and Life, Hassiba Benbouali University of Chlef, Chlef, Algeria
| | - Anthony Levasseur
- IHU Méditerranée Infection, Marseille, France.,Institut de Recherche pour le Développement (IRD), Assistance Publique- Hôpitaux de Marseille (AP-HM), MEPHI, Aix-Marseille Université, Marseille, France
| | - Bernard La Scola
- IHU Méditerranée Infection, Marseille, France.,Institut de Recherche pour le Développement (IRD), Assistance Publique- Hôpitaux de Marseille (AP-HM), MEPHI, Aix-Marseille Université, Marseille, France
| | - Philippe Colson
- IHU Méditerranée Infection, Marseille, France.,Institut de Recherche pour le Développement (IRD), Assistance Publique- Hôpitaux de Marseille (AP-HM), MEPHI, Aix-Marseille Université, Marseille, France
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