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Bottino P, Pastrone L, Curtoni A, Bondi A, Sidoti F, Zanotto E, Cavallo R, Solidoro P, Costa C. Antiviral Approach to Cytomegalovirus Infection: An Overview of Conventional and Novel Strategies. Microorganisms 2023; 11:2372. [PMID: 37894030 PMCID: PMC10608897 DOI: 10.3390/microorganisms11102372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Revised: 09/16/2023] [Accepted: 09/20/2023] [Indexed: 10/29/2023] Open
Abstract
Human cytomegalovirus (HCMV) is a herpesvirus capable of establishing a lifelong persistence in the host through a chronic state of infection and remains an essential global concern due to its distinct life cycle, mutations, and latency. It represents a life-threatening pathogen for immunocompromised patients, such as solid organ transplanted patients, HIV-positive individuals, and hematopoietic stem cell recipients. Multiple antiviral approaches are currently available and administered in order to prevent or manage viral infections in the early stages. However, limitations due to side effects and the onset of antidrug resistance are a hurdle to their efficacy, especially for long-term therapies. Novel antiviral molecules, together with innovative approaches (e.g., genetic editing and RNA interference) are currently in study, with promising results performed in vitro and in vivo. Since HCMV is a virus able to establish latent infection, with a consequential risk of reactivation, infection management could benefit from preventive treatment for critical patients, such as immunocompromised individuals and seronegative pregnant women. This review will provide an overview of conventional antiviral clinical approaches and their mechanisms of action. Additionally, an overview of proposed and developing new molecules is provided, including nucleic-acid-based therapies and immune-mediated approaches.
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Affiliation(s)
- Paolo Bottino
- Microbiology and Virology Unit, A.O.U. “Città della Salute e della Scienza di Torino”, 10126 Turin, Italy; (L.P.); (A.C.); (A.B.); (F.S.); (E.Z.); (R.C.)
| | - Lisa Pastrone
- Microbiology and Virology Unit, A.O.U. “Città della Salute e della Scienza di Torino”, 10126 Turin, Italy; (L.P.); (A.C.); (A.B.); (F.S.); (E.Z.); (R.C.)
| | - Antonio Curtoni
- Microbiology and Virology Unit, A.O.U. “Città della Salute e della Scienza di Torino”, 10126 Turin, Italy; (L.P.); (A.C.); (A.B.); (F.S.); (E.Z.); (R.C.)
| | - Alessandro Bondi
- Microbiology and Virology Unit, A.O.U. “Città della Salute e della Scienza di Torino”, 10126 Turin, Italy; (L.P.); (A.C.); (A.B.); (F.S.); (E.Z.); (R.C.)
| | - Francesca Sidoti
- Microbiology and Virology Unit, A.O.U. “Città della Salute e della Scienza di Torino”, 10126 Turin, Italy; (L.P.); (A.C.); (A.B.); (F.S.); (E.Z.); (R.C.)
| | - Elisa Zanotto
- Microbiology and Virology Unit, A.O.U. “Città della Salute e della Scienza di Torino”, 10126 Turin, Italy; (L.P.); (A.C.); (A.B.); (F.S.); (E.Z.); (R.C.)
| | - Rossana Cavallo
- Microbiology and Virology Unit, A.O.U. “Città della Salute e della Scienza di Torino”, 10126 Turin, Italy; (L.P.); (A.C.); (A.B.); (F.S.); (E.Z.); (R.C.)
| | - Paolo Solidoro
- Pneumology Unit, A.O.U. “Città della Salute e della Scienza di Torino”, 10126 Turin, Italy;
| | - Cristina Costa
- Microbiology and Virology Unit, A.O.U. “Città della Salute e della Scienza di Torino”, 10126 Turin, Italy; (L.P.); (A.C.); (A.B.); (F.S.); (E.Z.); (R.C.)
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Wang YQ, Zhao XY. Human Cytomegalovirus Primary Infection and Reactivation: Insights From Virion-Carried Molecules. Front Microbiol 2020; 11:1511. [PMID: 32765441 PMCID: PMC7378892 DOI: 10.3389/fmicb.2020.01511] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Accepted: 06/10/2020] [Indexed: 12/12/2022] Open
Abstract
Human cytomegalovirus (HCMV), a ubiquitous beta-herpesvirus, is able to establish lifelong latency after initial infection. Periodical reactivation occurs after immunosuppression, remaining a major cause of death in immunocompromised patients. HCMV has to reach a structural and functional balance with the host at its earliest entry. Virion-carried mediators are considered to play pivotal roles in viral adaptation into a new cellular environment upon entry. Additionally, one clear difference between primary infection and reactivation is the idea that virion-packaged factors are already formed such that those molecules can be used swiftly by the virus. In contrast, virion-carried mediators have to be transcribed and translated; thus, they are not readily available during reactivation. Hence, understanding virion-carried molecules helps to elucidate HCMV reactivation. In this article, the impact of virion-packaged molecules on viral structure, biological behavior, and viral life cycle will be reviewed.
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Affiliation(s)
- Yu-Qing Wang
- Peking University People's Hospital, Peking University Institute of Hematology, National Clinical Research Center for Hematologic Disease, Key Laboratory of Hematopoietic Stem Cell Transplantation, Beijing, China.,PKU-THU Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
| | - Xiang-Yu Zhao
- Peking University People's Hospital, Peking University Institute of Hematology, National Clinical Research Center for Hematologic Disease, Key Laboratory of Hematopoietic Stem Cell Transplantation, Beijing, China
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Nishimura M, Mori Y. Structural Aspects of Betaherpesvirus-Encoded Proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1045:227-249. [PMID: 29896670 DOI: 10.1007/978-981-10-7230-7_11] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
Betaherpesvirus possesses a large genome DNA with a lot of open reading frames, indicating abundance in the variety of viral protein factors. Because the complicated pathogenicity of herpesvirus reflects the combined functions of these factors, analyses of individual proteins are the fundamental steps to comprehensively understand about the viral life cycle and the pathogenicity. In this chapter, structural aspects of the betaherpesvirus-encoded proteins are introduced. Betaherpesvirus-encoded proteins of which structural information is available were summarized and subcategorized into capsid proteins, tegument proteins, nuclear egress complex proteins, envelope glycoproteins, enzymes, and immune-modulating factors. Structure of capsid proteins are analyzed in capsid by electron cryomicroscopy at quasi-atomic resolution. Structural information of teguments is limited, but a recent crystallographic analysis of an essential tegument protein of human herpesvirus 6B is introduced. As for the envelope glycoproteins, crystallographic analysis of glycoprotein gB has been done, revealing the fine-tuned structure and the distribution of its antigenic domains. gH/gL structure of betaherpesvirus is not available yet, but the overall shape and the spatial arrangement of the accessory proteins are analyzed by electron microscopy. Nuclear egress complex was analyzed from the structural perspective in 2015, with the structural analysis of cytomegalovirus UL50/UL53. The category "enzymes" includes the viral protease, DNA polymerase and terminase for which crystallographic analyses have been done. The immune-modulating factors are viral ligands or receptors for immune regulating factors of host immune cells, and their communications with host immune molecules are demonstrated in the aspect of molecular structure.
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Affiliation(s)
- Mitsuhiro Nishimura
- Division of Clinical Virology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
| | - Yasuko Mori
- Division of Clinical Virology, Center for Infectious Diseases, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan
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Mariamé B, Kappler-Gratias S, Kappler M, Balor S, Gallardo F, Bystricky K. Real-Time Visualization and Quantification of Human Cytomegalovirus Replication in Living Cells Using the ANCHOR DNA Labeling Technology. J Virol 2018; 92:e00571-18. [PMID: 29950406 PMCID: PMC6146708 DOI: 10.1128/jvi.00571-18] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 06/01/2018] [Indexed: 12/14/2022] Open
Abstract
Human cytomegalovirus (HCMV) induces latent lifelong infections in all human populations. Between 30% and nearly 100% of individuals are affected depending on the geographic area and socioeconomic conditions. The biology of the virus is difficult to explore due to its extreme sophistication and the lack of a pertinent animal model. Here, we present the first application of the ANCHOR DNA labeling system to a herpesvirus, enabling real-time imaging and direct monitoring of HCMV infection and replication in living human cells. The ANCHOR system is composed of a protein (OR) that specifically binds to a short, nonrepetitive DNA target sequence (ANCH) and spreads onto neighboring sequences by protein oligomerization. When the OR protein is fused to green fluorescent protein (GFP), its accumulation results in a site-specific fluorescent focus. We created a recombinant ANCHOR-HCMV harboring an ANCH target sequence and the gene encoding the cognate OR-GFP fusion protein. Infection of permissive cells with ANCHOR-HCMV enables visualization of nearly the complete viral cycle until cell fragmentation and death. Quantitative analysis of infection kinetics and of viral DNA replication revealed cell-type-specific HCMV behavior and sensitivity to inhibitors. Our results show that the ANCHOR technology provides an efficient tool for the study of complex DNA viruses and a new, highly promising system for the development of innovative biotechnology applications.IMPORTANCE The ANCHOR technology is currently the most powerful tool to follow and quantify the replication of HCMV in living cells and to gain new insights into its biology. The technology is applicable to virtually any DNA virus or viruses presenting a double-stranded DNA (dsDNA) phase, paving the way to imaging infection in various cell lines, or even in animal models, and opening fascinating fundamental and applied prospects. Associated with high-content automated microscopy, the technology permitted rapid, robust, and precise determination of ganciclovir 50% and 90% inhibitory concentrations (IC50 and IC90) on HCMV replication, with minimal hands-on time investment. To search for new antiviral activities, the experiment is easy to upgrade toward efficient and cost-effective screening of large chemical libraries. Simple infection of permissive cells with ANCHOR viruses in the presence of a compound of interest even provides a first estimation of the stage of the viral cycle the molecule is acting upon.
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Affiliation(s)
- Bernard Mariamé
- Laboratoire de Biologie Moléculaire Eucaryote (LBME), Centre de Biologie Intégrative (CBI), University of Toulouse, CNRS, UPS, Toulouse, France
- Institute for Advanced Life Science Technology (ITAV), University of Toulouse, CNRS, UPS, Toulouse, France
| | - Sandrine Kappler-Gratias
- Institute for Advanced Life Science Technology (ITAV), University of Toulouse, CNRS, UPS, Toulouse, France
- NeoVirTech SAS, Toulouse, France
| | | | - Stéphanie Balor
- Laboratoire de Biologie Moléculaire Eucaryote (LBME), Centre de Biologie Intégrative (CBI), University of Toulouse, CNRS, UPS, Toulouse, France
- Multiscale Electron Imaging (METi) Facility, Centre de Biologie Integrative (CBI), University of Toulouse, CNRS, UPS, Toulouse, France
| | - Franck Gallardo
- Institute for Advanced Life Science Technology (ITAV), University of Toulouse, CNRS, UPS, Toulouse, France
- NeoVirTech SAS, Toulouse, France
| | - Kerstin Bystricky
- Laboratoire de Biologie Moléculaire Eucaryote (LBME), Centre de Biologie Intégrative (CBI), University of Toulouse, CNRS, UPS, Toulouse, France
- Institute for Advanced Life Science Technology (ITAV), University of Toulouse, CNRS, UPS, Toulouse, France
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Marschall M, Muller YA, Diewald B, Sticht H, Milbradt J. The human cytomegalovirus nuclear egress complex unites multiple functions: Recruitment of effectors, nuclear envelope rearrangement, and docking to nuclear capsids. Rev Med Virol 2017; 27. [PMID: 28664574 DOI: 10.1002/rmv.1934] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Revised: 05/19/2017] [Accepted: 05/22/2017] [Indexed: 01/07/2023]
Abstract
BACKGROUND Nuclear replication represents a common hallmark of herpesviruses achieved by a number of sequentially unrolled regulatory processes. A rate-limiting step is provided by nucleo-cytoplasmic capsid export, for which a defined multiregulatory protein complex, namely, the nuclear egress complex (NEC), is assembled comprising both viral and cellular components. The NEC regulates at least 3 aspects of herpesviral nuclear replication: (1) multimeric recruitment of NEC-associated effector proteins, (2) reorganization of the nuclear lamina and membranes, and (3) the docking to nuclear capsids. Here, we review published data and own experimental work that characterizes the NEC of HCMV and other herpesviruses. METHODS A systematic review of information on nuclear egress of HCMV compared to selected alpha-, beta-, and gamma-herpesviruses: proteomics-based approaches, high-resolution imaging techniques, and functional investigations. RESULTS A large number of reports on herpesviral NECs have been published during the last two decades, focusing on protein-protein interactions, nuclear localization, regulatory phosphorylation, and functional validation. The emerging picture provides an illustrated example of well-balanced and sophisticated protein networking in virus-host interaction. CONCLUSIONS Current evidence refined the view about herpesviral NECs. Datasets published for HCMV, murine CMV, herpes simplex virus, and Epstein-Barr virus illustrate the marked functional consistency in the way herpesviruses achieve nuclear egress. However, this compares with only limited sequence conservation of core NEC proteins and a structural conservation restricted to individual domains. The translational use of this information might help to define a novel antiviral strategy on the basis of NEC-directed small molecules.
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Affiliation(s)
- Manfred Marschall
- Institute for Clinical and Molecular Virology, Friedrich-Alexander University of Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Yves A Muller
- Division of Biotechnology, Department of Biology, FAU, Erlangen, Germany
| | - Benedikt Diewald
- Division of Bioinformatics, Institute of Biochemistry, FAU, Erlangen, Germany
| | - Heinrich Sticht
- Division of Bioinformatics, Institute of Biochemistry, FAU, Erlangen, Germany
| | - Jens Milbradt
- Institute for Clinical and Molecular Virology, Friedrich-Alexander University of Erlangen-Nürnberg (FAU), Erlangen, Germany
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Sokolova OS, Shaburova OV, Pechnikova EV, Shaytan AK, Krylov SV, Kiselev NA, Krylov VN. Genome packaging in EL and Lin68, two giant phiKZ-like bacteriophages of P. aeruginosa. Virology 2014; 468-470:472-478. [PMID: 25254945 DOI: 10.1016/j.virol.2014.09.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Revised: 06/01/2014] [Accepted: 09/04/2014] [Indexed: 10/24/2022]
Abstract
A unique feature of the Pseudomonas aeruginosa giant phage phiKZ is its way of genome packaging onto a spool-like protein structure, the inner body. Until recently, no similar structures have been detected in other phages. We have studied DNA packaging in P. aeruginosa phages EL and Lin68 using cryo-electron microscopy and revealed the presence of inner bodies. The shape and positioning of the inner body and the density of the DNA packaging in EL are different from those found in phiKZ and Lin68. This internal organization explains how the shorter EL genome is packed into a large EL capsid, which has the same external dimensions as the capsids of phiKZ and Lin68. The similarity in the structural organization in EL and other phiKZ-like phages indicates that EL is phylogenetically related to other phiKZ-like phages, and, despite the lack of detectable DNA homology, EL, phiKZ, and Lin68 descend from a common ancestor.
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Affiliation(s)
- O S Sokolova
- M.V. Lomonosov Moscow State University, Moscow, Russia; A.V. Shoubnikov Institute of Crystallography RAS, Moscow, Russia.
| | - O V Shaburova
- I.I. Mechnikov Research Institute of Vaccines and Sera, RAMS, Moscow, Russia
| | - E V Pechnikova
- A.V. Shoubnikov Institute of Crystallography RAS, Moscow, Russia
| | - A K Shaytan
- M.V. Lomonosov Moscow State University, Moscow, Russia
| | - S V Krylov
- I.I. Mechnikov Research Institute of Vaccines and Sera, RAMS, Moscow, Russia
| | - N A Kiselev
- A.V. Shoubnikov Institute of Crystallography RAS, Moscow, Russia
| | - V N Krylov
- I.I. Mechnikov Research Institute of Vaccines and Sera, RAMS, Moscow, Russia
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Protein interactions in the murine cytomegalovirus capsid revealed by cryoEM. Protein Cell 2013; 4:833-45. [PMID: 24006185 DOI: 10.1007/s13238-013-3060-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Accepted: 08/14/2013] [Indexed: 10/26/2022] Open
Abstract
Cytomegalovirus (CMV) is distinct among members of the Herpesviridae family for having the largest dsDNA genome (230 kb). Packaging of large dsDNA genome is known to give rise to a highly pressurized viral capsid, but molecular interactions conducive to the formation of CMV capsid resistant to pressurization have not been described. Here, we report a cryo electron microscopy (cryoEM) structure of the murine cytomegalovirus (MCMV) capsid at a 9.1 Å resolution and describe the molecular interactions among the ∼3000 protein molecules in the MCMV capsid at the secondary structure level. Secondary structural elements are resolved to provide landmarks for correlating with results from sequence-based prediction and for structure-based homology modeling. The major capsid protein (MCP) upper domain (MCPud) contains α-helices and β-sheets conserved with those in MCPud of herpes simplex virus type 1 (HSV-1), with the largest differences identified as a "saddle loop" region, located at the tip of MCPud and involved in interaction with the smallest capsid protein (SCP). Interactions among the bacteriophage HK97-like floor domain of MCP, the middle domain of MCP, the hook and clamp domains of the triplex proteins (hoop and clamp domains of TRI-1 and clamp domain of TRI-2) contribute to the formation of a mature capsid. These results offer a framework for understanding how cytomegalovirus uses various secondary structural elements of its capsid proteins to build a robust capsid for packaging its large dsDNA genome inside and for attaching unique functional tegument proteins outside.
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The smallest capsid protein mediates binding of the essential tegument protein pp150 to stabilize DNA-containing capsids in human cytomegalovirus. PLoS Pathog 2013; 9:e1003525. [PMID: 23966856 PMCID: PMC3744435 DOI: 10.1371/journal.ppat.1003525] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Accepted: 06/14/2013] [Indexed: 11/20/2022] Open
Abstract
Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus that causes birth defects in newborns and life-threatening complications in immunocompromised individuals. Among all human herpesviruses, HCMV contains a much larger dsDNA genome within a similarly-sized capsid compared to the others, and it was proposed to require pp150, a tegument protein only found in cytomegaloviruses, to stabilize its genome-containing capsid. However, little is known about how pp150 interacts with the underlying capsid. Moreover, the smallest capsid protein (SCP), while dispensable in herpes simplex virus type 1, was shown to play essential, yet undefined, role in HCMV infection. Here, by cryo electron microscopy (cryoEM), we determine three-dimensional structures of HCMV capsid (no pp150) and virion (with pp150) at sub-nanometer resolution. Comparison of these two structures reveals that each pp150 tegument density is composed of two helix bundles connected by a long central helix. Correlation between the resolved helices and sequence-based secondary structure prediction maps the tegument density to the N-terminal half of pp150. The structures also show that SCP mediates interactions between the capsid and pp150 at the upper helix bundle of pp150. Consistent with this structural observation, ribozyme inhibition of SCP expression in HCMV-infected cells impairs the formation of DNA-containing viral particles and reduces viral yield by 10,000 fold. By cryoEM reconstruction of the resulting “SCP-deficient” viral particles, we further demonstrate that SCP is required for pp150 functionally binding to the capsid. Together, our structural and biochemical results point to a mechanism whereby SCP recruits pp150 to stabilize genome-containing capsid for the production of infectious HCMV virion. Human cytomegalovirus (HCMV) causes birth defects in newborns and life-threatening complications in immunocompromised individuals, such as AIDS patients and organ transplant recipients. The smallest capsid protein (SCP) – only 8 kDa molecular mass as compared to the 155 kDa major capsid protein – has been demonstrated to be essential for HCMV growth, but is dispensable in herpes simplex virus type 1. These seemingly contradictory observations have been a paradox. Here, we solve this paradox by high resolution cryo electron microscopy (cryoEM), in conjunction with functional studies using ribozyme inhibition. Our structural comparisons of HCMV virion and capsid reveal molecular interactions at the secondary structure level and suggest that SCP might contribute to capsid binding of pp150, an essential, cytomegalovirus-specific tegument protein. SCP-deficient particles generated by ribozyme inhibition of SCP-expression in HCMV-infected cells show no pp150 tegument density, demonstrating that SCP is required for the functional binding of pp150 to the capsid. Our results suggest that SCP recruits pp150 to stabilize the HCMV nucleocapsid to enable encapsidation of the genome, which is more densely packaged in HCMV than in other herpesviruses. Overall, this study not only resolves the above paradox, but also illustrates the passive acquisition of a new, essential function by SCP in the production of infectious HCMV virions.
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Germi R, Effantin G, Grossi L, Ruigrok RWH, Morand P, Schoehn G. Three-dimensional structure of the Epstein-Barr virus capsid. J Gen Virol 2012; 93:1769-1773. [PMID: 22592267 DOI: 10.1099/vir.0.043265-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Epstein-Barr virus (EBV), a gammaherpesvirus, infects >90 % of the world's population. Primary infection by EBV can lead to infectious mononucleosis, and EBV persistence is associated with several malignancies. Despite its importance for human health, little structural information is available on EBV. Here we report the purification of the EBV capsid by CsCl- or sucrose density-gradient centrifugation. Cryo-electron microscopy and image analysis resulted in two slightly different three-dimensional structures at about 20 Å resolution. These structures were compared with that of human herpesvirus 8, another gammaherpesvirus. CsCl-gradient purification leads to the removal of part of the triplex complex around the fivefold axes, whereas the complexes between hexons remained in place. This may be due to local differences in stability resulting from variation in quasi-equivalent interactions between pentons and hexons compared with those between hexons only.
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Affiliation(s)
- Raphaele Germi
- CHU de Grenoble, Grenoble, France.,Unit for Virus Host Cell Interactions, UMI 3265, Université Joseph Fourier-EMBL-CNRS, Grenoble, France
| | - Gregory Effantin
- Unit for Virus Host Cell Interactions, UMI 3265, Université Joseph Fourier-EMBL-CNRS, Grenoble, France
| | - Laurence Grossi
- CHU de Grenoble, Grenoble, France.,Unit for Virus Host Cell Interactions, UMI 3265, Université Joseph Fourier-EMBL-CNRS, Grenoble, France
| | - Rob W H Ruigrok
- Unit for Virus Host Cell Interactions, UMI 3265, Université Joseph Fourier-EMBL-CNRS, Grenoble, France
| | - Patrice Morand
- CHU de Grenoble, Grenoble, France.,Unit for Virus Host Cell Interactions, UMI 3265, Université Joseph Fourier-EMBL-CNRS, Grenoble, France
| | - Guy Schoehn
- CNRS - Institut de Biologie Structurale-Jean-Pierre Ebel, UMR 5075, 41 rue Jules Horowitz, 38027 Grenoble Cedex, France.,Unit for Virus Host Cell Interactions, UMI 3265, Université Joseph Fourier-EMBL-CNRS, Grenoble, France.,UJF-Grenoble-1 - Institut de Biologie Structurale-Jean-Pierre Ebel, UMR 5075, 41 rue Jules Horowitz, 38027 Grenoble Cedex, France.,CEA - Institut de Biologie Structurale-Jean-Pierre Ebel, UMR 5075, 41 rue Jules Horowitz, 38027 Grenoble Cedex, France
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Yu X, Shah S, Lee M, Dai W, Lo P, Britt W, Zhu H, Liu F, Zhou ZH. Biochemical and structural characterization of the capsid-bound tegument proteins of human cytomegalovirus. J Struct Biol 2011; 174:451-60. [PMID: 21459145 DOI: 10.1016/j.jsb.2011.03.006] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2010] [Revised: 02/24/2011] [Accepted: 03/11/2011] [Indexed: 01/25/2023]
Abstract
Human cytomegalovirus (HCMV) is the most genetically and structurally complex human herpesvirus and is composed of an envelope, a tegument, and a dsDNA-containing capsid. HCMV tegument plays essential roles in HCMV infection and assembly. Using cryo electron tomography (cryoET), here we show that HCMV tegument compartment can be divided into two sub-compartments: an inner and an outer tegument. The inner tegument consists of densely-packed proteins surrounding the capsid. The outer tegument contains those components that are loosely packed in the space between the inner tegument and the pleomorphic glycoprotein-containing envelope. To systematically characterize the inner tegument proteins interacting with the capsid, we used chemical treatment to strip off the entire envelope and most tegument proteins to obtain a tegumented capsid with inner tegument proteins. SDS-polyacrylamide gel electrophoresis analyses show that only two tegument proteins, UL32-encoded pp150 and UL48-encoded high molecular weight protein (HMWP), remains unchanged in their abundance in the tegumented capsids as compared to their abundance in the intact particles. Three-dimensional reconstructions by single particle cryo electron microscopy (cryoEM) reveal that the net-like layer of icosahedrally-ordered tegument densities are also the same in the tegumented capsid and in the intact particles. CryoET reconstruction of the tegumented capsid labeled with an anti-pp150 antibody is consistent with the biochemical and cryoEM data in localizing pp150 within the ordered tegument. Taken together, these results suggest that pp150, a betaherpesvirus-specific tegument protein, is a constituent of the net-like layer of icosahedrally-ordered capsid-bound tegument densities, a structure lacking similarities in alpha and gammaherpesviruses.
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Affiliation(s)
- Xuekui Yu
- Department of Microbiology, Immunology and Molecular Genetics, University of California at Los Angeles, USA
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11
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Abstract
SUMMARY Human cytomegalovirus (HCMV) is a common, medically relevant human herpesvirus. The tegument layer of herpesvirus virions lies between the genome-containing capsids and the viral envelope. Proteins within the tegument layer of herpesviruses are released into the cell upon entry when the viral envelope fuses with the cell membrane. These proteins are fully formed and active and control viral entry, gene expression, and immune evasion. Most tegument proteins accumulate to high levels during later stages of infection, when they direct the assembly and egress of progeny virions. Thus, viral tegument proteins play critical roles at the very earliest and very last steps of the HCMV lytic replication cycle. This review summarizes HCMV tegument composition and structure as well as the known and speculated functions of viral tegument proteins. Important directions for future investigation and the challenges that lie ahead are identified and discussed.
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12
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Dai W, Jia Q, Bortz E, Shah S, Liu J, Atanasov I, Li X, Taylor KA, Sun R, Zhou ZH. Unique structures in a tumor herpesvirus revealed by cryo-electron tomography and microscopy. J Struct Biol 2007; 161:428-38. [PMID: 18096403 DOI: 10.1016/j.jsb.2007.10.010] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2007] [Revised: 10/12/2007] [Accepted: 10/13/2007] [Indexed: 11/17/2022]
Abstract
Gammaherpesviruses, including the human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, are causative agents of lymphomas and other malignancies. The structural characterization of these viruses has been limited due to difficulties in obtaining adequate amount of virion particles. Here we report the first three-dimensional structural characterization of a whole gammaherpesvirus virion by an emerging integrated approach of cryo-electron tomography combined with single-particle cryo-electron microscopy, using murine gammaherpesvirus-68 (MHV-68) as a model system. We found that the MHV-68 virion consists of distinctive envelope and tegument compartments, and a highly conserved nucleocapsid. Two layers of tegument are identified: an inner tegument layer tethered to the underlying capsid and an outer, flexible tegument layer conforming to the overlying, pleomorphic envelope, consistent with the sequential viral tegumentation process inside host cells. Surprisingly, comparison of the MHV-68 virion and capsid reconstructions shows that the interactions between the capsid and inner tegument proteins are completely different from those observed in alpha and betaherpesviruses. These observations support the notion that the inner layer tegument across different subfamilies of herpesviruses has evolved significantly to confer specific characteristics related to viral-host interactions, in contrast to a highly conserved capsid for genome encapsidation and protection.
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Affiliation(s)
- Wei Dai
- Department of Pathology and Laboratory Medicine, University of Texas Medical School at Houston, Houston, TX 77030, USA
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13
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Yu X, Trang P, Shah S, Atanasov I, Kim YH, Bai Y, Zhou ZH, Liu F. Dissecting human cytomegalovirus gene function and capsid maturation by ribozyme targeting and electron cryomicroscopy. Proc Natl Acad Sci U S A 2005; 102:7103-8. [PMID: 15883374 PMCID: PMC1091747 DOI: 10.1073/pnas.0408826102] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human CMV (HCMV) is the leading viral cause of birth defects and causes one of the most common opportunistic infections among transplant recipients and AIDS patients. Cleavage of internal scaffolding proteins by the viral protease (Pr) occurs during HCMV capsid assembly. To gain insight into the mechanism of HCMV capsid maturation and the roles of the Pr in viral replication, an RNase P ribozyme was engineered to target the Pr mRNA and down-regulate its expression by >99%, generating premature Pr-minus capsids. Furthermore, scaffolding protein processing and DNA encapsidation were inhibited by 99%, and viral growth was reduced by 10,000-fold. 3D structural comparison of the Pr-minus and wild-type B capsids by electron cryomicroscopy, at an unprecedented 12.5-angstroms resolution, unexpectedly revealed that the structures are identical in their overall shape and organization. However, the Pr-minus capsid contains tenuous connections between the scaffold and the capsid shell, whereas the wild-type B capsid has extra densities in its core that may represent the viral Pr. Our findings indicate that cleavage of the scaffolding protein is not associated with the morphological changes that occur during capsid maturation. Instead, the protease appears to be required for DNA encapsidation and the subsequent maturation steps leading to infectious progeny. These results therefore provide key insights into an essential step of HCMV infection using an RNase P ribozyme-based inhibition strategy.
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Affiliation(s)
- Xuekui Yu
- Division of Infectious Diseases, School of Public Health, University of California, Berkeley, CA 94720, USA
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14
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Yu X, Shah S, Atanasov I, Lo P, Liu F, Britt WJ, Zhou ZH. Three-dimensional localization of the smallest capsid protein in the human cytomegalovirus capsid. J Virol 2005; 79:1327-32. [PMID: 15613360 PMCID: PMC538561 DOI: 10.1128/jvi.79.2.1327-1332.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The smallest capsid proteins (SCPs) of the human herpesviruses differ substantially in size and sequence and are thought to impart some unique aspects of infection to their respective viruses. We used electron cryomicroscopy and antibody labeling to show that the 8-kDa SCP of human cytomegalovirus is attached only to major capsid protein subunits of the hexons, not the pentons. Thus, the SCPs of different herpesviruses illustrate that a protein can evolve significantly in sequence, structure, and function, while preserving its role in the architecture of the virus by binding to a specific partner in a specific oligomeric state.
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Affiliation(s)
- Xuekui Yu
- Department of Pathology and Laboratory Medicine, University of Texas Medical School at Houston, 6431 Fannin St., MSB 2.280, Houston, TX 77030, USA
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15
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Rosenke K, Fortunato EA. Bromodeoxyuridine-labeled viral particles as a tool for visualization of the immediate-early events of human cytomegalovirus infection. J Virol 2004; 78:7818-22. [PMID: 15220456 PMCID: PMC434117 DOI: 10.1128/jvi.78.14.7818-7822.2004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2003] [Accepted: 03/17/2004] [Indexed: 11/20/2022] Open
Abstract
We describe here a simple method for labeling the genome of human cytomegalovirus, a large double-stranded DNA virus, with bromodeoxyuridine (BrdU). The labeled DNA was incorporated into viral particles, which were then collected in cell supernatant. To demonstrate the versatility and effectiveness of this method, labeled virions were used to study the immediate-early events of virus-host cell interaction via indirect immunofluorescence microscopy. It is our hope that this new methodology will prove useful in the study of binding, entry and viral genome deposition in diverse virus systems.
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Affiliation(s)
- Kyle Rosenke
- Deptartment of Microbiology, University of Idaho, Moscow, ID 83844-3052, USA
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16
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Yu XK, O'Connor CM, Atanasov I, Damania B, Kedes DH, Zhou ZH. Three-dimensional structures of the A, B, and C capsids of rhesus monkey rhadinovirus: insights into gammaherpesvirus capsid assembly, maturation, and DNA packaging. J Virol 2004; 77:13182-93. [PMID: 14645575 PMCID: PMC296048 DOI: 10.1128/jvi.77.24.13182-13193.2003] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rhesus monkey rhadinovirus (RRV) exhibits high levels of sequence homology to human gammaherpesviruses, such as Kaposi's sarcoma-associated herpesvirus, and grows to high titers in cell cultures, making it a good model system for studying gammaherpesvirus capsid structure and assembly. We have purified RRV A, B, and C capsids, thus for the first time allowing direct structure comparisons by electron cryomicroscopy and three-dimensional reconstruction. The results show that the shells of these capsids are identical and are each composed of 12 pentons, 150 hexons, and 320 triplexes. Structural differences were apparent inside the shells and through the penton channels. The A capsid is empty, and its penton channels are open. The B capsid contains a scaffolding core, and its penton channels are closed. The C capsid contains a DNA genome, which is closely packaged into regularly spaced density shells (25 A apart), and its penton channels are open. The different statuses of the penton channels suggest a functional role of the channels during capsid maturation, and the overall structural similarities of RRV capsids to alphaherpesvirus capsids suggest a common assembly and maturation pathway. The RRV A capsid reconstruction at a 15-A resolution, the best achieved for gammaherpesvirus particles, reveals overall structural similarities to alpha- and betaherpesvirus capsids. However, the outer regions of the capsid, including densities attributed to the Ta triplex and the small capsomer-interacting protein (SCIP or ORF65), exhibit prominent differences from their structural counterparts in alphaherpesviruses. This structural disparity suggests that SCIP and the triplex, together with tegument and envelope proteins, confer structural and potentially functional specificities to alpha-, beta-, and gammaherpesviruses.
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Affiliation(s)
- Xue-Kui Yu
- Department of PathologyLaboratory Medicine, University of Texas at Houston Medical School, Houston, Texas 77030, USA
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17
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Bortz E, Whitelegge JP, Jia Q, Zhou ZH, Stewart JP, Wu TT, Sun R. Identification of proteins associated with murine gammaherpesvirus 68 virions. J Virol 2004; 77:13425-32. [PMID: 14645600 PMCID: PMC296060 DOI: 10.1128/jvi.77.24.13425-13432.2003] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Murine gammaherpesvirus 68 (MHV68 [also known as gammaHV-68]) is distinguished by its ability to replicate to high titers in cultured cells, making it an excellent candidate for studying gammaherpesvirus virion composition. Extracellular MHV68 virions were isolated, and abundant virion-associated proteins were identified by mass spectrometry. Five nucleocapsid protein homologues, the tegument protein homologue encoded by open reading frame (ORF) 75c, and envelope glycoproteins B and H were detected. In addition, gene products from MHV68 ORF20, ORF24, ORF28, ORF45, ORF48, and ORF52 were identified in association with virions, suggesting that these gammaherpesvirus genes are involved in the early phase of infection or virion assembly and egress.
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Affiliation(s)
- Eric Bortz
- Molecular Biology Institute, University of California at Los Angeles, Los Angeles, California 90095, USA
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18
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Borst EM, Messerle M. Construction of a cytomegalovirus-based amplicon: a vector with a unique transfer capacity. Hum Gene Ther 2003; 14:959-70. [PMID: 12869214 DOI: 10.1089/104303403766682223] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Cytomegalovirus (CMV) has a number of interesting properties that qualifies it as a vector for gene transfer. Especially appealing is the ability of the CMV genome to persist in hematopoietic progenitor cells and the packaging capacity of the viral capsid that accommodates a DNA genome of 230 kbp. In order to exploit the packaging capacity of the CMV capsid we investigated whether the principles of an amplicon vector can be applied to CMV. Amplicons are herpesviral vectors, which contain only the cis-active sequences required for replication and packaging of the vector genome. For construction of a CMV amplicon the sequences comprising the lytic origin of replication (orilyt) and the cleavage packaging recognition sites (pac) of human CMV were cloned onto a plasmid. A gene encoding the green fluorescent protein was used as a model transgene. The amplicon plasmid replicated in the presence of a CMV helper virus and was packaged into CMV particles, with replication and packaging being dependent on the presence of the orilyt and pac sequences. The packaged amplicon could be transferred to recipient cells and reisolated from the transduced cells. Analysis of the DNA isolated from CMV capsids revealed that the CMV amplicon was packaged as a concatemer with a size of approximately 210 kbp. The CMV amplicon vector has the potential to transfer therapeutic genes with a size of more than 200 kbp and thus provides a unique transfer capacity among viral vectors.
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Affiliation(s)
- Eva Maria Borst
- Virus Cell Interaction Group, Medical Faculty, University of Halle-Wittenberg, 06120 Halle (Saale), Germany
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19
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Abstract
Human cytomegalovirus (HCMV), a betaherpesvirus, represents the major infectious cause of birth defects, as well as an important pathogen for immunocompromised individuals. The viral nucleocapsid containing a linear double-stranded DNA of 230 kb is surrounded by a proteinaceous tegument, which is itself enclosed by a loosely applied lipid bilayer. Expression of the HCMV genome is controlled by a cascade of transcriptional events that leads to the synthesis of three categories of viral proteins designated as immediate-early, early, and late. Clinical manifestations can be seen following primary infection, reinfection, or reactivation. About 10% of infants are infected by the age of 6 months following transmission from their mothers via the placenta, during delivery, or by breastfeeding. HCMV is a significant post-allograft pathogen and contributes to graft loss independently from graft rejection. Histopathologic examination of necropsy tissues demonstrates that the virus enters via the epithelium of the upper alimentary, respiratory, or genitourinary tracts. Hematogenous spreading is typically followed by infection of ductal epithelial cells. Infections are kept under control by the immune system. However, total HCMV clearance is rarely achieved, and the viral genome remains at selected sites in a latent state. Virological and molecular detection of HCMV, as well as serological demonstration of a specific immune response, are used for diagnosis. Treatment of HCMV infections is difficult because there are few options. The presently available drugs produced a significant clinical improvement, but suffer from poor oral bioavailability, low potency, development of resistance in clinical practice, and dose-limiting toxicities.
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Affiliation(s)
- Santo Landolfo
- Department of Public Health and Microbiology, University of Turin, Via Santena 9, 10126 Turin, Italy.
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20
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Lo P, Yu X, Atanasov I, Chandran B, Zhou ZH. Three-dimensional localization of pORF65 in Kaposi's sarcoma-associated herpesvirus capsid. J Virol 2003; 77:4291-7. [PMID: 12634386 PMCID: PMC150664 DOI: 10.1128/jvi.77.7.4291-4297.2003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Of the six herpesvirus capsid proteins, the smallest capsid proteins (SCPs) share the least sequence homology among herpesvirus family members and have been implicated in virus specificity during infection. The herpes simplex virus-1 (HSV-1) SCP was shown to be horn shaped and to specifically bind the upper domain of each major capsid protein in hexons but not in pentons. In Kaposi's sarcoma-associated herpesvirus (KSHV), the protein encoded by the ORF65 gene (pORF65) is the putative SCP but its location remains controversial due to the absence of such horn-shaped densities from both the pentons and hexons of the KSHV capsid reconstructions. To directly locate the KSHV SCP, we have used electron cryomicroscopy and three-dimensional reconstruction techniques to compare the three-dimensional structure of KSHV capsids to that of anti-pORF65 antibody-labeled capsids. Our difference map shows prominent antibody densities bound to the tips of the hexons but not to pentons, indicating that KSHV SCP is attached to the upper domain of the major capsid protein in hexons but not to that in pentons, similar to HSV-1 SCP. The lack of horn-shaped densities on the hexons indicates that KSHV SCP exhibits structural features that are substantially different from those of HSV-1 SCP. The location of SCP at the outermost regions of the capsid suggests a possible role in mediating capsid interactions with the tegument and cytoskeletal proteins during infection.
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Affiliation(s)
- Pierrette Lo
- Department of Pathology and Laboratory Medicine, University of Texas-Houston Medical School, Houston, Texas 77030, USA
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21
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Abstract
In this article we have attempted to describe some structural aspects of large viruses. Although this may seem a straightforward task, it is complicated by the fact that large viruses do not represent a distinctive class of organisms and any grouping under this heading will include a range of unrelated viruses with different structures, replication strategies, and host types. To simplify matters we limited our definition to dsDNA viruses with genomes of 100 kbp or larger. However, even this restricted grouping includes viruses with diverse and seemingly unrelated structures. Furthermore, few if any structural features are exclusive to large viruses and most of what appears distinctive about their structure or assembly can also be found in smaller, and usually better characterized, viruses. Therefore we have not attempted to provide a comprehensive catalog of the properties of large viruses but have tried to illustrate particular structural points with examples from a few of the better known forms, notably herpes simplex virus (HSV) and phage T4. The two techniques used to provide rigorous analyses of virus structures are X-ray crystallography and electron cryomicroscopy with computer-assisted reconstruction. To date, X-ray crystallography has been successful only with smaller viruses, and what is known about the structures of these large viruses has come primarily from electron cryomicroscopy. However, with the notable exception of the HSV capsid, such studies have been limited in extent and of relatively low resolution, and the information obtained has been confined largely to describing the spatial distributions and relationships between the subunits. Nevertheless, these studies have given us our clearest insights into the biology of these complex particles and increases in resolution promise to extend these insights by bridging the gap between gross and atomic structures, as exemplified by the identification and mapping of secondary structural elements in the HSV capsid.
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Affiliation(s)
- Frazer J Rixon
- MRC Virology Unit, Institute of Virology, Glasgow G11 5JR, United Kingdom
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22
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Cheng N, Trus BL, Belnap DM, Newcomb WW, Brown JC, Steven AC. Handedness of the herpes simplex virus capsid and procapsid. J Virol 2002; 76:7855-9. [PMID: 12097597 PMCID: PMC136369 DOI: 10.1128/jvi.76.15.7855-7859.2002] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The capsid of herpes simplex virus has an icosahedral surface lattice with a nonskew triangulation number, T=16. Nevertheless, the proteins arrayed on this lattice necessarily have an intrinsic handedness. We have determined the handedness of both the herpes simplex virus type 1 capsid and its precursor procapsid by a cryoelectron microscopic tilting method.
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Affiliation(s)
- Naiqian Cheng
- Laboratory of Structural Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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23
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Adair R, Douglas ER, Maclean JB, Graham SY, Aitken JD, Jamieson FE, Dargan DJ. The products of human cytomegalovirus genes UL23, UL24, UL43 and US22 are tegument components. J Gen Virol 2002; 83:1315-1324. [PMID: 12029146 DOI: 10.1099/0022-1317-83-6-1315] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have investigated the human cytomegalovirus (HCMV) US22 gene family members UL23, UL24, UL43 and US22. Specific antibodies were generated to identify pUL23 (33 kDa), pUL24 (40 kDa) and pUL43 (48 kDa), while pUS22 was identified by monoclonal antibody HWLF1. A C-terminally truncated UL43 product (pUL43t; 21 kDa) produced by a deletion mutant was also investigated. The UL24 and UL43 genes were expressed with early-late (gamma1) and true-late (gamma2) kinetics, respectively. Immunoblot and immuno-EM studies demonstrated that pUL23, pUL24, pUL43 and pUS22 were virion tegument components. Immunofluorescence and immuno-EM studies showed that pUL23, pUL24, pUL43 and pUL43t were located in cytoplasmic protein aggregates, manifesting two forms: complex juxtanuclear structures and smaller, membrane-bound aggregates resembling dense bodies. The complex-type aggregate is a putative site of particle maturation. Because pUL43t was present in protein aggregates, but under-represented in virus particles compared to pUL43, it was concluded that N-terminal sequences target pUL43 to protein aggregates and that C-terminal sequences are important for incorporation into particles. Since three other US22 family products (pUL36, pTRS1 and pIRS1) are documented tegument components, at least seven of the twelve US22 family genes encode tegument proteins, suggesting that the products of the remaining five genes might be similarly located. These findings demonstrate a common biological feature among most, if not all, US22 family proteins and implicate the family in events occurring immediately after virus penetration.
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Affiliation(s)
- Richard Adair
- MRC Virology Unit, Church Street, Glasgow G11 5JR, UK1
| | | | | | | | - James D Aitken
- Division of Virology, Institute of Biomedical and Life Sciences, University of Glasgow, Church Street, Glasgow G11 5JR, UK2
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24
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Trus BL, Heymann JB, Nealon K, Cheng N, Newcomb WW, Brown JC, Kedes DH, Steven AC. Capsid structure of Kaposi's sarcoma-associated herpesvirus, a gammaherpesvirus, compared to those of an alphaherpesvirus, herpes simplex virus type 1, and a betaherpesvirus, cytomegalovirus. J Virol 2001; 75:2879-90. [PMID: 11222713 PMCID: PMC115914 DOI: 10.1128/jvi.75.6.2879-2890.2001] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The capsid of Kaposi's sarcoma-associated herpesvirus (KSHV) was visualized at 24-A resolution by cryoelectron microscopy. Despite limited sequence similarity between corresponding capsid proteins, KSHV has the same T=16 triangulation number and much the same capsid architecture as herpes simplex virus (HSV) and cytomegalovirus (CMV). Its capsomers are hexamers and pentamers of the major capsid protein, forming a shell with a flat, close-packed, inner surface (the "floor") and chimney-like external protrusions. Overlying the floor at trigonal positions are (alpha beta(2)) heterotrimers called triplexes. The floor structure is well conserved over all three viruses, and the most variable capsid features reside on the outer surface, i.e., in the shapes of the protrusions and triplexes, in which KSHV resembles CMV and differs from HSV. Major capsid protein sequences from the three subfamilies have some similarity, which is closer between KSHV and CMV than between either virus and HSV. The triplex proteins are less highly conserved, but sequence analysis identifies relatively conserved tracts. In alphaherpesviruses, the alpha-subunit (VP19c in HSV) has a 100-residue N-terminal extension and an insertion near the C terminus. The small basic capsid protein sequences are highly divergent: whereas the HSV and CMV proteins bind only to hexons, difference mapping suggests that the KSHV protein, ORF65, binds around the tips of both hexons and pentons.
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Affiliation(s)
- B L Trus
- Laboratory of Structural Biology, National Institute of Arthritis, Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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25
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Borst EM, Mathys S, Wagner M, Muranyi W, Messerle M. Genetic evidence of an essential role for cytomegalovirus small capsid protein in viral growth. J Virol 2001; 75:1450-8. [PMID: 11152518 PMCID: PMC114051 DOI: 10.1128/jvi.75.3.1450-1458.2001] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Many steps in the replication cycle of cytomegalovirus (CMV), like cell entry, capsid assembly, and egress of newly synthesized virions, have not been completely analyzed yet. In order to facilitate these studies, we decided to construct a recombinant CMV that incorporates the green fluorescent protein (GFP) into the nucleocapsid. A comparable herpes simplex virus type 1 (HSV-1) mutant has recently been generated by fusion of the GFP open reading frame (ORF) with the HSV-1 ORF encoding small capsid protein (SCP) VP26 (P. Desai and S. Person, J. Virol. 72:7563-7568, 1998). Recombinant CMV genomes expressing a fusion protein consisting of GFP and the SCP were constructed by the recently established bacterial artificial chromosome mutagenesis procedure. In transfected cells, the SCP-GFP fusion protein localized to distinct foci in the nucleus that may represent sites for capsid assembly (assemblons). However, no viable progeny was reconstituted from these mutant CMV genomes. CMV genomes with deletion of the SCP ORF also did not give rise to infectious virus. Rescue of the mutation by insertion of the SCP gene at an ectopic position in an SCP knockout genome indicates that, in contrast to the HSV-1 SCP, the CMV SCP is essential for viral growth. Expression of the SCP-GFP fusion protein together with the authentic SCP blocked the CMV infection cycle, suggesting that the SCP-GFP fusion protein exerts a dominant-negative effect on the assembly of new virions. The results of this study are discussed with regard to recently published data about the structure of the CMV virion and its differences from the HSV-1 virion.
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Affiliation(s)
- E M Borst
- Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Lehrstuhl Virologie, Genzentrum, Ludwig-Maximilians-Universität München, D-81377 Munich, Germany
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26
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Wu L, Lo P, Yu X, Stoops JK, Forghani B, Zhou ZH. Three-dimensional structure of the human herpesvirus 8 capsid. J Virol 2000; 74:9646-54. [PMID: 11000237 PMCID: PMC112397 DOI: 10.1128/jvi.74.20.9646-9654.2000] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2000] [Accepted: 07/13/2000] [Indexed: 11/20/2022] Open
Abstract
Human herpesvirus 8 (HHV-8), or Kaposi's sarcoma-associated herpesvirus, is a gammaherpesvirus implicated in all forms of Kaposi's sarcoma and certain lymphomas. HHV-8 has been extensively characterized, both biochemically and immunologically, since its first description in 1994. However, its three-dimensional (3D) structure remained heretofore undetermined largely due to difficulties in viral purification. We have used log-phase cultures of body cavity-based lymphoma 1 cells induced with 12-O-tetradecanoylphorbol-13-acetate to obtain HHV-8 capsids for electron cryomicroscopy and computer reconstruction. The 3D structure of the HHV-8 capsids revealed a capsid shell composed of 12 pentons, 150 hexons, and 320 triplexes arranged on a T=16 icosahedral lattice. This structure is similar to those of herpes simplex virus type 1 (HSV-1) and human cytomegalovirus (HCMV), which are prototypical members of alpha- and betaherpesviruses, respectively. The inner radius of the HHV-8 capsid is identical to that of the HSV-1 capsid but is smaller than that of the HCMV capsid, which is consistent with the relative sizes of the genomes they enclose. While the HHV-8 capsid exhibits many structural similarities to the HSV-1 capsid, our reconstruction shows two major differences: its hexons lack the "horn-shaped" VP26 densities bound to the HSV-1 hexon subunits, and the HHV-8 triplexes appear smaller and less elongated than those of HSV-1. These differences are in excellent agreement with our sequence comparisons of HHV-8 and HSV-1 capsid proteins. This gammaherpesvirus capsid structure complements previous structural studies on alpha- and betaherpesviruses in providing an account of structural similarities and differences among capsids representing all human herpesvirus subfamilies.
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Affiliation(s)
- L Wu
- Viral and Rickettsial Disease Laboratory, Division of Communicable Disease Control, California Department of Health Services, Berkeley, California 94720, USA
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27
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Kivioja T, Ravantti J, Verkhovsky A, Ukkonen E, Bamford D. Local average intensity-based method for identifying spherical particles in electron micrographs. J Struct Biol 2000; 131:126-34. [PMID: 11042083 DOI: 10.1006/jsbi.2000.4279] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
A method is presented that reliably detects spherical viruses from a wide variety of noisy low-contrast electron micrographs. Such detection is one of the first image analysis steps in the computer-aided reconstruction of three-dimensional density distribution models of viruses. Particle detection is based on the comparison of intensity in a circular area and in the surrounding ring followed by a number of tests to validate the potential particles. The only required input from the user in addition to the micrograph is an approximate radius of the particle. The method has been implemented as program ETHAN that has been tested for several different data sets. ETHAN has also successfully been used to detect DNA-less virus particles for an actual reconstruction.
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Affiliation(s)
- T Kivioja
- Department of Computer Science, University of Helsinki, 00014, Finland
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28
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Bhella D, Rixon FJ, Dargan DJ. Cryomicroscopy of human cytomegalovirus virions reveals more densely packed genomic DNA than in herpes simplex virus type 1. J Mol Biol 2000; 295:155-61. [PMID: 10623515 DOI: 10.1006/jmbi.1999.3344] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
All members of the herpesvirus family have a characteristic virion structure, comprising a DNA containing, icosahedral capsid, embedded in a proteinaceous layer (tegument) and surrounded by a lipid envelope. Human cytomegalovirus (HCMV, the prototypic beta-herpesvirus) has a genome that is significantly larger (>50 %) than that of the alpha-herpesvirus HSV-1. Although the internal volume of the HCMV capsid is approximately 17 % larger than that of HSV-1, this slight increase in volume does not provide adequate space to encapsidate the full length HCMV genome at the same packing density as HSV-1. We have investigated the nature of DNA packing in HCMV and HSV-1 virions by electron-cryomicroscopy and image processing. Radial density profiles calculated from projection images of HCMV and HSV-1 capsids suggest that there is no increase in the volume of the HCMV capsid upon DNA packaging. Packing density of the viral DNA was assessed for both HCMV and HSV-1 by image analysis of both full and empty particles. Our results for packing density in HSV-1 are in good agreement with previously published measurements, showing an average inter-layer spacing of approximately 26 A. Measurements taken from our HCMV images, however, suggest that the viral genomic DNA is more densely packed, with an average inter-layer spacing of approximately 23 A. We propose therefore, that the combination of greater volume in HCMV capsids and increased packing density of viral DNA accounts for its ability to encapsidate a large genome.
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Affiliation(s)
- D Bhella
- Medical Research Council Virology Unit, Church Street, Glasgow, G11 5JR, United Kingdom.
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Baker TS, Olson NH, Fuller SD. Adding the third dimension to virus life cycles: three-dimensional reconstruction of icosahedral viruses from cryo-electron micrographs. Microbiol Mol Biol Rev 1999; 63:862-922, table of contents. [PMID: 10585969 PMCID: PMC98980 DOI: 10.1128/mmbr.63.4.862-922.1999] [Citation(s) in RCA: 367] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Viruses are cellular parasites. The linkage between viral and host functions makes the study of a viral life cycle an important key to cellular functions. A deeper understanding of many aspects of viral life cycles has emerged from coordinated molecular and structural studies carried out with a wide range of viral pathogens. Structural studies of viruses by means of cryo-electron microscopy and three-dimensional image reconstruction methods have grown explosively in the last decade. Here we review the use of cryo-electron microscopy for the determination of the structures of a number of icosahedral viruses. These studies span more than 20 virus families. Representative examples illustrate the use of moderate- to low-resolution (7- to 35-A) structural analyses to illuminate functional aspects of viral life cycles including host recognition, viral attachment, entry, genome release, viral transcription, translation, proassembly, maturation, release, and transmission, as well as mechanisms of host defense. The success of cryo-electron microscopy in combination with three-dimensional image reconstruction for icosahedral viruses provides a firm foundation for future explorations of more-complex viral pathogens, including the vast number that are nonspherical or nonsymmetrical.
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Affiliation(s)
- T S Baker
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-1392, USA.
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Chen DH, Jiang H, Lee M, Liu F, Zhou ZH. Three-dimensional visualization of tegument/capsid interactions in the intact human cytomegalovirus. Virology 1999; 260:10-6. [PMID: 10405351 DOI: 10.1006/viro.1999.9791] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The three-dimensional structure of the intact human cytomegalovirus (HCMV) was determined to 18-A resolution by electron cryomicroscopy and computer reconstruction. Its capsid shell is composed of pentons, hexons, and triplexes arranged on a T = 16 icosahedral lattice and is identical to that of the B-capsid isolated from host cell nuclei. An icosahedrally ordered tegument layer formed by 960 copies of filamentous density is also visualized, which interacts with the pentons, hexons, and triplexes of the underlying capsid. The observed structural similarities and differences of HCMV with those of herpes simplex virus offer insights into the significance of the different tegument components for their infection processes while maintaining similar capsids.
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Affiliation(s)
- D H Chen
- Department of Pathology and Laboratory Medicine, University of Texas-Houston Medical School, Houston, Texas, 77030, USA
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