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Skidmore AM, Bradfute SB. The life cycle of the alphaviruses: From an antiviral perspective. Antiviral Res 2023; 209:105476. [PMID: 36436722 PMCID: PMC9840710 DOI: 10.1016/j.antiviral.2022.105476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 11/18/2022] [Accepted: 11/21/2022] [Indexed: 11/27/2022]
Abstract
The alphaviruses are a widely distributed group of positive-sense, single stranded, RNA viruses. These viruses are largely arthropod-borne and can be found on all populated continents. These viruses cause significant human disease, and recently have begun to spread into new populations, such as the expansion of Chikungunya virus into southern Europe and the Caribbean, where it has established itself as endemic. The study of alphaviruses is an active and expanding field, due to their impacts on human health, their effects on agriculture, and the threat that some pose as potential agents of biological warfare and terrorism. In this systematic review we will summarize both historic knowledge in the field as well as recently published data that has potential to shift current theories in how alphaviruses are able to function. This review is comprehensive, covering all parts of the alphaviral life cycle as well as a brief overview of their pathology and the current state of research in regards to vaccines and therapeutics for alphaviral disease.
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Affiliation(s)
- Andrew M Skidmore
- Center for Global Health, Department of Internal Medicine, University of New Mexico Health Sciences Center, 915 Camino de Salud, IDTC Room 3245, Albuquerque, NM, 87131, USA.
| | - Steven B Bradfute
- Center for Global Health, Department of Internal Medicine, University of New Mexico Health Sciences Center, 915 Camino de Salud, IDTC Room 3330A, Albuquerque, NM, 87131, USA.
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2
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Wang X, Zhu J, Zhang D, Liu G. Ribosomal control in RNA virus-infected cells. Front Microbiol 2022; 13:1026887. [PMID: 36419416 PMCID: PMC9677555 DOI: 10.3389/fmicb.2022.1026887] [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: 08/24/2022] [Accepted: 10/19/2022] [Indexed: 11/09/2022] Open
Abstract
Viruses are strictly intracellular parasites requiring host cellular functions to complete their reproduction cycle involving virus infection of host cell, viral genome replication, viral protein translation, and virion release. Ribosomes are protein synthesis factories in cells, and viruses need to manipulate ribosomes to complete their protein synthesis. Viruses use translation initiation factors through their own RNA structures or cap structures, thereby inducing ribosomes to synthesize viral proteins. Viruses also affect ribosome production and the assembly of mature ribosomes, and regulate the recognition of mRNA by ribosomes, thereby promoting viral protein synthesis and inhibiting the synthesis of host antiviral immune proteins. Here, we review the remarkable mechanisms used by RNA viruses to regulate ribosomes, in particular, the mechanisms by which RNA viruses induce the formation of specific heterogeneous ribosomes required for viral protein translation. This review provides valuable insights into the control of viral infection and diseases from the perspective of viral protein synthesis.
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TMEΜ45B Interacts with Sindbis Virus Nsp1 and Nsp4 and Inhibits Viral Replication. J Virol 2022; 96:e0091922. [PMID: 35938871 PMCID: PMC9472651 DOI: 10.1128/jvi.00919-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Alphavirus infection induces the expression of type I interferons, which inhibit the viral replication by upregulating the expression of interferon-stimulated genes (ISGs). Identification and mechanistic studies of the antiviral ISGs help to better understand how the host controls viral infection and help to better understand the viral replication process. Here, we report that the ISG product TMEM45B inhibits the replication of Sindbis virus (SINV). TMEM45B is a transmembrane protein that was detected mainly in the trans-Golgi network, endosomes, and lysosomes but not obviously at the plasma membrane or endoplasmic reticulum. TMEM45B interacted with the viral nonstructural proteins Nsp1 and Nsp4 and inhibited the translation and promoted the degradation of SINV RNA. TMEM45B overexpression rendered the intracellular membrane-associated viral RNA sensitive to RNase treatment. In line with these results, the formation of cytopathic vacuoles (CPVs) was dramatically diminished in TMEM45B-expressing cells. TMEM45B also interacted with Nsp1 and Nsp4 of chikungunya virus (CHIKV), suggesting that it may also inhibit the replication of other alphaviruses. These findings identified TMEM45B as an antiviral factor against alphaviruses and help to better understand the process of the viral genome replication. IMPORTANCE Alphaviruses are positive-stranded RNA viruses with more than 30 members. Infection with Old World alphaviruses, which comprise some important human pathogens such as chikungunya virus and Ross River virus, rarely results in fatal diseases but can lead to high morbidity in humans. Infection with New World alphaviruses usually causes serious encephalitis but low morbidity in humans. Alphavirus infection induces the expression of type I interferons, which subsequently upregulate hundreds of interferon-stimulated genes. Identification and characterization of host antiviral factors help to better understand how the viruses can establish effective infection. Here, we identified TMEM45B as a novel interferon-stimulated antiviral factor against Sindbis virus, a prototype alphavirus. TMEM45B interacted with viral proteins Nsp1 and Nsp4, interfered with the interaction between Nsp1 and Nsp4, and inhibited the viral replication. These findings provide insights into the detailed process of the viral replication and help to better understand the virus-host interactions.
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Mayaro Virus: The State-of-the-Art for Antiviral Drug Development. Viruses 2022; 14:v14081787. [PMID: 36016409 PMCID: PMC9415492 DOI: 10.3390/v14081787] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 08/10/2022] [Accepted: 08/11/2022] [Indexed: 12/18/2022] Open
Abstract
Mayaro virus is an emerging arbovirus that causes nonspecific febrile illness or arthralgia syndromes similar to the Chikungunya virus, a virus closely related from the Togaviridae family. MAYV outbreaks occur more frequently in the northern and central-western states of Brazil; however, in recent years, virus circulation has been spreading to other regions. Due to the undifferentiated initial clinical symptoms between MAYV and other endemic pathogenic arboviruses with geographic overlapping, identification of patients infected by MAYV might be underreported. Additionally, the lack of specific prophylactic approaches or antiviral drugs limits the pharmacological management of patients to treat symptoms like pain and inflammation, as is the case with most pathogenic alphaviruses. In this context, this review aims to present the state-of-the-art regarding the screening and development of compounds/molecules which may present anti-MAYV activity and infection inhibition.
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Mangala Prasad V, Blijleven JS, Smit JM, Lee KK. Visualization of conformational changes and membrane remodeling leading to genome delivery by viral class-II fusion machinery. Nat Commun 2022; 13:4772. [PMID: 35970990 PMCID: PMC9378758 DOI: 10.1038/s41467-022-32431-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Accepted: 07/31/2022] [Indexed: 11/09/2022] Open
Abstract
Chikungunya virus (CHIKV) is a human pathogen that delivers its genome to the host cell cytoplasm through endocytic low pH-activated membrane fusion mediated by class-II fusion proteins. Though structures of prefusion, icosahedral CHIKV are available, structural characterization of virion interaction with membranes has been limited. Here, we have used cryo-electron tomography to visualize CHIKV's complete membrane fusion pathway, identifying key intermediary glycoprotein conformations coupled to membrane remodeling events. Using sub-tomogram averaging, we elucidate features of the low pH-exposed virion, nucleocapsid and full-length E1-glycoprotein's post-fusion structure. Contrary to class-I fusion systems, CHIKV achieves membrane apposition by protrusion of extended E1-glycoprotein homotrimers into the target membrane. The fusion process also features a large hemifusion diaphragm that transitions to a wide pore for intact nucleocapsid delivery. Our analyses provide comprehensive ultrastructural insights into the class-II virus fusion system function and direct mechanistic characterization of the fundamental process of protein-mediated membrane fusion.
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Affiliation(s)
- Vidya Mangala Prasad
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA.,Molecular Biophysics Unit, Indian Institute of Science, Bengaluru, Karnataka, India
| | - Jelle S Blijleven
- Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Jolanda M Smit
- Department of Medical Microbiology and Infection Prevention, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
| | - Kelly K Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA. .,Biological Physics, Structure and Design Graduate Program, University of Washington, Seattle, WA, USA. .,Department of Microbiology, University of Washington, Seattle, WA, USA.
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6
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Capsid-E2 Interactions Rescue Core Assembly in Viruses That Cannot Form Cytoplasmic Nucleocapsid Cores. J Virol 2021; 95:e0106221. [PMID: 34495691 DOI: 10.1128/jvi.01062-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Alphavirus capsid proteins (CPs) have two domains: the N-terminal domain (NTD), which interacts with the viral RNA, and the C-terminal domain (CTD), which forms CP-CP interactions and interacts with the cytoplasmic domain of the E2 spike protein (cdE2). In this study, we examine how mutations in the CP NTD affect CP CTD interactions with cdE2. We changed the length and/or charge of the NTD of Ross River virus CP and found that changing the charge of the NTD has a greater impact on core and virion assembly than changing the length of the NTD. The NTD CP insertion mutants are unable to form cytoplasmic cores during infection, but they do form cores or core-like structures in virions. Our results are consistent with cdE2 having a role in core maturation during virion assembly and rescuing core formation when cytoplasmic cores are not assembled. We go on to find that the isolated cores from some mutant virions are now assembly competent in that they can be disassembled and reassembled back into cores. These results show how the two domains of CP may have distinct yet coordinated roles. IMPORTANCE Structural viral proteins have multiple roles during entry and assembly. The capsid protein (CP) of alphaviruses has one domain that interacts with the viral genome and another domain that interacts with the E2 spike protein. In this work, we determined that the length and/or charge of the CP affects cytoplasmic core formation. However, defects in cytoplasmic core formation can be overcome by E2-CP interactions, thus assembling a core or core-like complex in the virion. In the absence of both cytoplasmic cores and CP-E2 interactions, CP is not even packaged in the released virions, but some infectious particles are still released, presumably as RNA packaged in a glycoprotein-containing membrane shell. This suggests that the virus has multiple mechanisms in place to ensure the viral genome is surrounded by a capsid core during its life cycle.
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Elmasri Z, Nasal BL, Jose J. Alphavirus-Induced Membrane Rearrangements during Replication, Assembly, and Budding. Pathogens 2021; 10:984. [PMID: 34451448 PMCID: PMC8399458 DOI: 10.3390/pathogens10080984] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 07/30/2021] [Accepted: 08/02/2021] [Indexed: 01/01/2023] Open
Abstract
Alphaviruses are arthropod-borne viruses mainly transmitted by hematophagous insects that cause moderate to fatal disease in humans and other animals. Currently, there are no approved vaccines or antivirals to mitigate alphavirus infections. In this review, we summarize the current knowledge of alphavirus-induced structures and their functions in infected cells. Throughout their lifecycle, alphaviruses induce several structural modifications, including replication spherules, type I and type II cytopathic vacuoles, and filopodial extensions. Type I cytopathic vacuoles are replication-induced structures containing replication spherules that are sites of RNA replication on the endosomal and lysosomal limiting membrane. Type II cytopathic vacuoles are assembly induced structures that originate from the Golgi apparatus. Filopodial extensions are induced at the plasma membrane and are involved in budding and cell-to-cell transport of virions. This review provides an overview of the viral and host factors involved in the biogenesis and function of these virus-induced structures. Understanding virus-host interactions in infected cells will lead to the identification of new targets for antiviral discovery.
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Affiliation(s)
- Zeinab Elmasri
- Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA;
- Department of Biochemistry & Molecular Biology, Eberly College of Science, The Pennsylvania State University, University Park, PA 16802, USA;
| | - Benjamin L. Nasal
- Department of Biochemistry & Molecular Biology, Eberly College of Science, The Pennsylvania State University, University Park, PA 16802, USA;
| | - Joyce Jose
- Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA;
- Department of Biochemistry & Molecular Biology, Eberly College of Science, The Pennsylvania State University, University Park, PA 16802, USA;
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Hasan SS, Dey D, Singh S, Martin M. The Structural Biology of Eastern Equine Encephalitis Virus, an Emerging Viral Threat. Pathogens 2021; 10:pathogens10080973. [PMID: 34451437 PMCID: PMC8400090 DOI: 10.3390/pathogens10080973] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Revised: 07/21/2021] [Accepted: 07/28/2021] [Indexed: 11/16/2022] Open
Abstract
Alphaviruses are arboviruses that cause arthritis and encephalitis in humans. Eastern Equine Encephalitis Virus (EEEV) is a mosquito-transmitted alphavirus that is implicated in severe encephalitis in humans with high mortality. However, limited insights are available into the fundamental biology of EEEV and residue-level details of its interactions with host proteins. In recent years, outbreaks of EEEV have been reported mainly in the United States, raising concerns about public safety. This review article summarizes recent advances in the structural biology of EEEV based mainly on single-particle cryogenic electron microscopy (cryoEM) structures. Together with functional analyses of EEEV and related alphaviruses, these structural investigations provide clues to how EEEV interacts with host proteins, which may open avenues for the development of therapeutics.
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Affiliation(s)
- S. Saif Hasan
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 N. Greene Street, Baltimore, MD 21201, USA; (D.D.); (S.S.); (M.M.)
- Center for Biomolecular Therapeutics, University of Maryland School of Medicine, 9600 Gudelsky Drive, Rockville, MD 20850, USA
- University of Maryland Marlene and Stewart Greenebaum Cancer Center, University of Maryland Medical Center, 22. S. Greene St., Baltimore, MD 21201, USA
- Correspondence:
| | - Debajit Dey
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 N. Greene Street, Baltimore, MD 21201, USA; (D.D.); (S.S.); (M.M.)
| | - Suruchi Singh
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 N. Greene Street, Baltimore, MD 21201, USA; (D.D.); (S.S.); (M.M.)
| | - Matthew Martin
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 N. Greene Street, Baltimore, MD 21201, USA; (D.D.); (S.S.); (M.M.)
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Contu L, Balistreri G, Domanski M, Uldry AC, Mühlemann O. Characterisation of the Semliki Forest Virus-host cell interactome reveals the viral capsid protein as an inhibitor of nonsense-mediated mRNA decay. PLoS Pathog 2021; 17:e1009603. [PMID: 34019569 PMCID: PMC8174725 DOI: 10.1371/journal.ppat.1009603] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 06/03/2021] [Accepted: 05/03/2021] [Indexed: 01/08/2023] Open
Abstract
The positive-sense, single-stranded RNA alphaviruses pose a potential epidemic threat. Understanding the complex interactions between the viral and the host cell proteins is crucial for elucidating the mechanisms underlying successful virus replication strategies and for developing specific antiviral interventions. Here we present the first comprehensive protein-protein interaction map between the proteins of Semliki Forest Virus (SFV), a mosquito-borne member of the alphaviruses, and host cell proteins. Among the many identified cellular interactors of SFV proteins, the enrichment of factors involved in translation and nonsense-mediated mRNA decay (NMD) was striking, reflecting the virus' hijacking of the translation machinery and indicating viral countermeasures for escaping NMD by inhibiting NMD at later time points during the infectious cycle. In addition to observing a general inhibition of NMD about 4 hours post infection, we also demonstrate that transient expression of the SFV capsid protein is sufficient to inhibit NMD in cells, suggesting that the massive production of capsid protein during the SFV reproduction cycle is responsible for NMD inhibition.
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Affiliation(s)
- Lara Contu
- Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
- Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland
| | - Giuseppe Balistreri
- Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland
- Queensland Brain Institute, The University of Queensland, Brisbane, Australia
| | - Michal Domanski
- Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
| | - Anne-Christine Uldry
- Proteomics & Mass Spectrometry Core Facility, Department for BioMedical Research, University of Bern, Bern, Switzerland
| | - Oliver Mühlemann
- Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
- * E-mail:
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Cryo-EM Structures of Eastern Equine Encephalitis Virus Reveal Mechanisms of Virus Disassembly and Antibody Neutralization. Cell Rep 2019; 25:3136-3147.e5. [PMID: 30540945 PMCID: PMC6302666 DOI: 10.1016/j.celrep.2018.11.067] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Revised: 10/01/2018] [Accepted: 11/15/2018] [Indexed: 01/08/2023] Open
Abstract
Alphaviruses are enveloped pathogens that cause arthritis and encephalitis. Here, we report a 4.4-Å cryoelectron microscopy (cryo-EM) structure of eastern equine encephalitis virus (EEEV), an alphavirus that causes fatal encephalitis in humans. Our analysis provides insights into viral entry into host cells. The envelope protein E2 showed a binding site for the cellular attachment factor heparan sulfate. The presence of a cryptic E2 glycan suggests how EEEV escapes surveillance by lectin-expressing myeloid lineage cells, which are sentinels of the immune system. A mechanism for nucleocapsid core release and disassembly upon viral entry was inferred based on pH changes and capsid dissociation from envelope proteins. The EEEV capsid structure showed a viral RNA genome binding site adjacent to a ribosome binding site for viral genome translation following genome release. Using five Fab-EEEV complexes derived from neutralizing antibodies, our investigation provides insights into EEEV host cell interactions and protective epitopes relevant to vaccine design. EEEV cryo-EM structure shows the basis of receptor binding and pH-triggered disassembly Cryptic envelope protein glycosylation interferes with immune detection EEEV RNA genome binding site on capsid protein has an extended conformation Antibody inhibition of EEEV entry involves cross-linking of viral envelope proteins
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Brown RS, Wan JJ, Kielian M. The Alphavirus Exit Pathway: What We Know and What We Wish We Knew. Viruses 2018; 10:E89. [PMID: 29470397 PMCID: PMC5850396 DOI: 10.3390/v10020089] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 02/19/2018] [Accepted: 02/20/2018] [Indexed: 12/28/2022] Open
Abstract
Alphaviruses are enveloped positive sense RNA viruses and include serious human pathogens, such as the encephalitic alphaviruses and Chikungunya virus. Alphaviruses are transmitted to humans primarily by mosquito vectors and include species that are classified as emerging pathogens. Alphaviruses assemble highly organized, spherical particles that bud from the plasma membrane. In this review, we discuss what is known about the alphavirus exit pathway during a cellular infection. We describe the viral protein interactions that are critical for virus assembly/budding and the host factors that are involved, and we highlight the recent discovery of cell-to-cell transmission of alphavirus particles via intercellular extensions. Lastly, we discuss outstanding questions in the alphavirus exit pathway that may provide important avenues for future research.
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Affiliation(s)
- Rebecca S Brown
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | - Judy J Wan
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | - Margaret Kielian
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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Abstract
Cleavage of the alphavirus precursor glycoprotein p62 into the E2 and E3 glycoproteins before assembly with the nucleocapsid is the key to producing fusion-competent mature spikes on alphaviruses. Here we present a cryo-EM, 6.8-Å resolution structure of an "immature" Chikungunya virus in which the cleavage site has been mutated to inhibit proteolysis. The spikes in the immature virus have a larger radius and are less compact than in the mature virus. Furthermore, domains B on the E2 glycoproteins have less freedom of movement in the immature virus, keeping the fusion loops protected under domain B. In addition, the nucleocapsid of the immature virus is more compact than in the mature virus, protecting a conserved ribosome-binding site in the capsid protein from exposure. These differences suggest that the posttranslational processing of the spikes and nucleocapsid is necessary to produce infectious virus.
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Lundberg L, Carey B, Kehn-Hall K. Venezuelan Equine Encephalitis Virus Capsid-The Clever Caper. Viruses 2017; 9:E279. [PMID: 28961161 PMCID: PMC5691631 DOI: 10.3390/v9100279] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Revised: 09/23/2017] [Accepted: 09/26/2017] [Indexed: 01/13/2023] Open
Abstract
Venezuelan equine encephalitis virus (VEEV) is a New World alphavirus that is vectored by mosquitos and cycled in rodents. It can cause disease in equines and humans characterized by a febrile illness that may progress into encephalitis. Like the capsid protein of other viruses, VEEV capsid is an abundant structural protein that binds to the viral RNA and interacts with the membrane-bound glycoproteins. It also has protease activity, allowing cleavage of itself from the growing structural polypeptide during translation. However, VEEV capsid protein has additional nonstructural roles within the host cell functioning as the primary virulence factor for VEEV. VEEV capsid inhibits host transcription and blocks nuclear import in mammalian cells, at least partially due to its complexing with the host CRM1 and importin α/β1 nuclear transport proteins. VEEV capsid also shuttles between the nucleus and cytoplasm and is susceptible to inhibitors of nuclear trafficking, making it a promising antiviral target. Herein, the role of VEEV capsid in viral replication and pathogenesis will be discussed including a comparison to proteins of other alphaviruses.
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Affiliation(s)
- Lindsay Lundberg
- National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University, Manassas, VA 20110, USA.
| | - Brian Carey
- National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University, Manassas, VA 20110, USA.
| | - Kylene Kehn-Hall
- National Center for Biodefense and Infectious Diseases, School of Systems Biology, George Mason University, Manassas, VA 20110, USA.
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14
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Tang J, Jose J, Chipman P, Zhang W, Kuhn RJ, Baker TS. Molecular links between the E2 envelope glycoprotein and nucleocapsid core in Sindbis virus. J Mol Biol 2011; 414:442-59. [PMID: 22001018 DOI: 10.1016/j.jmb.2011.09.045] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Revised: 09/26/2011] [Accepted: 09/28/2011] [Indexed: 10/17/2022]
Abstract
A three-dimensional reconstruction of Sindbis virus at 7.0 Å resolution presented here provides a detailed view of the virion structure and includes structural evidence for key interactions that occur between the capsid protein (CP) and transmembrane (TM) glycoproteins E1 and E2. Based on crystal structures of component proteins and homology modeling, we constructed a nearly complete, pseudo-atomic model of the virus. Notably, this includes identification of the 33-residue cytoplasmic domain of E2 (cdE2), which follows a path from the E2 TM helix to the CP where it enters and exits the CP hydrophobic pocket and then folds back to contact the viral membrane. Modeling analysis identified three major contact regions between cdE2 and CP, and the roles of specific residues were probed by molecular genetics. This identified R393 and E395 of cdE2 and Y162 and K252 of CP as critical for virus assembly. The N-termini of the CPs form a contiguous network that interconnects 12 pentameric and 30 hexameric CP capsomers. A single glycoprotein spike cross-links three neighboring CP capsomers as might occur during initiation of virus budding.
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Affiliation(s)
- Jinghua Tang
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0378, USA
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15
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Zhang R, Hryc CF, Cong Y, Liu X, Jakana J, Gorchakov R, Baker ML, Weaver SC, Chiu W. 4.4 Å cryo-EM structure of an enveloped alphavirus Venezuelan equine encephalitis virus. EMBO J 2011; 30:3854-63. [PMID: 21829169 PMCID: PMC3173789 DOI: 10.1038/emboj.2011.261] [Citation(s) in RCA: 152] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Accepted: 07/08/2011] [Indexed: 11/09/2022] Open
Abstract
Venezuelan equine encephalitis virus (VEEV), a member of the membrane-containing Alphavirus genus, is a human and equine pathogen, and has been developed as a biological weapon. Using electron cryo-microscopy (cryo-EM), we determined the structure of an attenuated vaccine strain, TC-83, of VEEV to 4.4 Å resolution. Our density map clearly resolves regions (including E1, E2 transmembrane helices and cytoplasmic tails) that were missing in the crystal structures of domains of alphavirus subunits. These new features are implicated in the fusion, assembly and budding processes of alphaviruses. Furthermore, our map reveals the unexpected E3 protein, which is cleaved and generally thought to be absent in the mature VEEV. Our structural results suggest a mechanism for the initial stage of nucleocapsid core formation, and shed light on the virulence attenuation, host recognition and neutralizing activities of VEEV and other alphavirus pathogens.
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Affiliation(s)
- Rui Zhang
- Graduate Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, TX, USA
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Replication of alphaviruses: a review on the entry process of alphaviruses into cells. Adv Virol 2011; 2011:249640. [PMID: 22312336 PMCID: PMC3265296 DOI: 10.1155/2011/249640] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Accepted: 05/03/2011] [Indexed: 02/04/2023] Open
Abstract
Alphaviruses are small, enveloped viruses, ~70 nm in diameter, containing a single-stranded, positive-sense, RNA genome. Viruses belonging to this genus are predominantly arthropod-borne viruses, known to cause disease in humans. Their potential threat to human health was most recently exemplified by the 2005 Chikungunya virus outbreak in La Reunion, highlighting the necessity to understand events in the life-cycle of these medically important human pathogens. The replication and propagation of viruses is dependent on entry into permissive cells. Viral entry is initiated by attachment of virions to cells, leading to internalization, and uncoating to release genetic material for replication and propagation. Studies on alphaviruses have revealed entry via a receptor-mediated, endocytic pathway. In this paper, the different stages of alphavirus entry are examined, with examples from Semliki Forest virus, Sindbis virus, Chikungunya virus, and Venezuelan equine encephalitis virus described.
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Abstract
The study of alphavirus entry has been complicated by an inability to clearly identify a receptor and by experiments which only tangentially and indirectly examine the process, producing results that are difficult to interpret. The mechanism of entry has been widely accepted to be by endocytosis followed by acidification of the endosome resulting in virus membrane-endosome membrane fusion. This mechanism has come under scrutiny as better purification protocols and improved methods of analysis have been brought to the study. Results have been obtained that suggest alphaviruses infect cells directly at the plasma membrane without the involvement of endocytosis, exposure to acid pH, or membrane fusion. In this review we compare the data which support the two models and make the case for an alternative pathway of entry by alphaviruses.
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Abstract
Alphaviruses are small, spherical, enveloped, positive-sense, single-stranded, RNA viruses responsible for considerable human and animal disease. Using microinjection of preassembled cores as a tool, a system has been established to study the assembly and budding process of Sindbis virus, the type member of the alphaviruses. We demonstrate the release of infectious virus-like particles from cells expressing Sindbis virus envelope glycoproteins following microinjection of Sindbis virus nucleocapsids purified from the cytoplasm of infected cells. Furthermore, it is shown that nucleocapsids assembled in vitro mimic those isolated in the cytoplasm of infected cells with respect to their ability to be incorporated into enveloped virions following microinjection. This system allows for the study of the alphavirus budding process independent of an authentic infection and provides a platform to study viral and host requirements for budding.
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Solignat M, Gay B, Higgs S, Briant L, Devaux C. Replication cycle of chikungunya: a re-emerging arbovirus. Virology 2009; 393:183-97. [PMID: 19732931 PMCID: PMC2915564 DOI: 10.1016/j.virol.2009.07.024] [Citation(s) in RCA: 229] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Revised: 07/07/2009] [Accepted: 07/22/2009] [Indexed: 12/13/2022]
Abstract
Arboviruses (or arthropod-borne viruses), represent a threat for the new century. The 2005-2006 year unprecedented epidemics of chikungunya virus (CHIKV) in the French Reunion Island in the Indian Ocean, followed by several outbreaks in other parts of the world such as India, have attracted the attention of clinicians, scientists, and state authorities about the risks linked to this re-emerging mosquito-borne virus. CHIKV, which belongs to the Alphaviruses genus, was not previously regarded as a highly pathogenic arbovirus. However, this opinion was challenged by the death of several CHIKV-infected persons in Reunion Island. The epidemic episode began in December 2005 and four months later the seroprevalence survey report indicated that 236,000 persons, more than 30% of Reunion Island population, had been infected with CHIKV, among which 0.4-0.5% of cases were fatal. Since the epidemic peak, the infection case number has continued to increase to almost 40% of the population, with a total of more than 250 fatalities. Although information available on CHIKV is growing quite rapidly, we are still far from understanding the strategies required for the ecologic success of this virus, virus replication, its interactions with its vertebrate hosts and arthropod vectors, and its genetic evolution. In this paper, we summarize the current knowledge of CHIKV genomic organization, cell tropism, and the virus replication cycle, and evaluate the possibility to predict its future evolution. Such understanding may be applied in order to anticipate future epidemics and reduce the incidence by development and application of, for example, vaccination and antiviral therapy.
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Affiliation(s)
- Maxime Solignat
- Université Montpellier 1, Centre d'études d'agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier, France
- CNRS, UMR5236, CPBS, F-34965 Montpellier, France
- Université Montpellier 2, CPBS, F-34095 Montpellier, France
| | - Bernard Gay
- Université Montpellier 1, Centre d'études d'agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier, France
- CNRS, UMR5236, CPBS, F-34965 Montpellier, France
- Université Montpellier 2, CPBS, F-34095 Montpellier, France
| | - Stephen Higgs
- Department of Pathology, University of Texas Medical Branch, Galveston, Texas, USA
| | - Laurence Briant
- Université Montpellier 1, Centre d'études d'agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier, France
- CNRS, UMR5236, CPBS, F-34965 Montpellier, France
- Université Montpellier 2, CPBS, F-34095 Montpellier, France
| | - Christian Devaux
- Université Montpellier 1, Centre d'études d'agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier, France
- CNRS, UMR5236, CPBS, F-34965 Montpellier, France
- Université Montpellier 2, CPBS, F-34095 Montpellier, France
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20
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Jose J, Snyder JE, Kuhn RJ. A structural and functional perspective of alphavirus replication and assembly. Future Microbiol 2009; 4:837-56. [PMID: 19722838 DOI: 10.2217/fmb.09.59] [Citation(s) in RCA: 234] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Alphaviruses are small, spherical, enveloped, positive-sense ssRNA viruses responsible for a considerable number of human and animal diseases. Alphavirus members include Chikungunya virus, Sindbis virus, Semliki Forest virus, the western, eastern and Venezuelan equine encephalitis viruses, and the Ross River virus. Alphaviruses can cause arthritic diseases and encephalitis in humans and animals and continue to be a worldwide threat. The viruses are transmitted by blood-sucking arthropods, and replicate in both arthropod and vertebrate hosts. Alphaviruses form spherical particles (65-70 nm in diameter) with icosahedral symmetry and a triangulation number of four. The icosahedral structures of alphaviruses have been defined to very high resolutions by cryo-electron microscopy and crystallographic studies. In this review, we summarize the major events in alphavirus infection: entry, replication, assembly and budding. We focus on data acquired from structural and functional studies of the alphaviruses. These structural and functional data provide a broader perspective of the virus lifecycle and structure, and allow additional insight into these important viruses.
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Affiliation(s)
- Joyce Jose
- Department of Biological Sciences, Bindley Bioscience Center, Lilly Hall of Life Sciences, 915 West State St., Purdue University, West Lafayette, IN 47907, USA.
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21
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The regulation of disassembly of alphavirus cores. Arch Virol 2009; 154:381-90. [PMID: 19225713 DOI: 10.1007/s00705-009-0333-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2008] [Accepted: 01/22/2009] [Indexed: 10/21/2022]
Abstract
Alphaviruses are used as model viruses for structure determination and for analysis of virus entry. They are used also as vectors for protein expression and gene therapy. Virus particles are assembled by budding, using preformed cores and a modified cellular membrane. During entry, alphaviruses release the viral core into the cytoplasm. Cores are disassembled during virus entry and accumulate in the cytoplasm during virus multiplication. The regulation of core disassembly is the subject of this review. A working model compatible with all experimental data is formulated. This model comprises the following steps: (1) The incoming core is present in the cytoplasm in a metastable state, primed for disassembly. A core structure containing the so-called linker region of the core protein in an exposed position susceptible to proteolytic cleavage on the core surface might represent the primed state. (2) The primed core allows access of cellular proteins to the viral genome RNA, e.g. initiation factors of protein synthesis. (3) In a following step, ribosomal 60S subunits bind to the complex and lead to core disassembly with a concomitant transfer of core protein or of core protein fragments to the 28S rRNA. The linker region may be involved in this transfer. (4) During the later stages of virus multiplication, cellular components involved in step (2) and/or in step (3) are inactivated. This inactivation might involve the binding of newly synthesised core protein to 28S rRNA. (5) Unprimed cores, e.g. core particles containing the linker region in an unexposed position, are assembled during virus multiplication. Priming of cores and inactivation of host-cell factors each represent a complete mechanism of regulation of core disassembly. Future experiments will show whether or not both processes are actually used. Since alphaviruses, e.g. Chikungunya virus, Ross River virus, Semliki Forest virus, and Sindbis virus, are human pathogens, these experiments are of practical relevance, since they might identify targets for antiviral chemotherapy.
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22
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Role of sindbis virus capsid protein region II in nucleocapsid core assembly and encapsidation of genomic RNA. J Virol 2008; 82:4461-70. [PMID: 18305029 DOI: 10.1128/jvi.01936-07] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Sindbis virus is an enveloped positive-sense RNA virus in the alphavirus genus. The nucleocapsid core contains the genomic RNA surrounded by 240 copies of a single capsid protein. The capsid protein is multifunctional, and its roles include acting as a protease, controlling the specificity of RNA that is encapsidated into nucleocapsid cores, and interacting with viral glycoproteins to promote the budding of mature virus and the release of the genomic RNA into the newly infected cell. The region comprising amino acids 81 to 113 was previously implicated in two processes, the encapsidation of the viral genomic RNA and the stable accumulation of nucleocapsid cores in the cytoplasm of infected cells. In the present study, specific amino acids within this region responsible for the encapsidation of the genomic RNA have been identified. The region that is responsible for nucleocapsid core accumulation has considerable overlap with the region that controls encapsidation specificity.
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23
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Garmashova N, Atasheva S, Kang W, Weaver SC, Frolova E, Frolov I. Analysis of Venezuelan equine encephalitis virus capsid protein function in the inhibition of cellular transcription. J Virol 2007; 81:13552-65. [PMID: 17913819 PMCID: PMC2168819 DOI: 10.1128/jvi.01576-07] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The encephalitogenic New World alphaviruses, including Venezuelan (VEEV), eastern (EEEV), and western equine encephalitis viruses, constitute a continuing public health threat in the United States. They circulate in Central, South, and North America and have the ability to cause fatal disease in humans and in horses and other domestic animals. We recently demonstrated that these viruses have developed the ability to interfere with cellular transcription and use it as a means of downregulating a cellular antiviral response. The results of the present study suggest that the N-terminal, approximately 35-amino-acid-long peptide of VEEV and EEEV capsid proteins plays the most critical role in the downregulation of cellular transcription and development of a cytopathic effect. The identified VEEV-specific peptide C(VEE)33-68 includes two domains with distinct functions: the alpha-helix domain, helix I, which is critically involved in supporting the balance between the presence of the protein in the cytoplasm and nucleus, and the downstream peptide, which might contain a functional nuclear localization signal(s). The integrity of both domains not only determines the intracellular distribution of the VEEV capsid but is also essential for direct capsid protein functioning in the inhibition of transcription. Our results suggest that the VEEV capsid protein interacts with the nuclear pore complex, and this interaction correlates with the protein's ability to cause transcriptional shutoff and, ultimately, cell death. The replacement of the N-terminal fragment of the VEEV capsid by its Sindbis virus-specific counterpart in the VEEV TC-83 genome does not affect virus replication in vitro but reduces cytopathogenicity and results in attenuation in vivo. These findings can be used in designing a new generation of live, attenuated, recombinant vaccines against the New World alphaviruses.
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Affiliation(s)
- Natalia Garmashova
- Department of Microbiology and Immunology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-1019, USA
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24
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Wu SR, Haag L, Hammar L, Wu B, Garoff H, Xing L, Murata K, Cheng RH. The dynamic envelope of a fusion class II virus. Prefusion stages of semliki forest virus revealed by electron cryomicroscopy. J Biol Chem 2006; 282:6752-62. [PMID: 17192272 DOI: 10.1074/jbc.m609125200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Semliki Forest virus is among the prototypes for Class II virus fusion and targets the endosomal membrane. Fusion protein E1 and its envelope companion E2 are both anchored in the viral membrane and form an external shell with protruding spikes. In acid environments, mimicking the early endosomal milieu, surface epitopes in the virus rearrange along with exposure of the fusion loop. To visualize this transformation into a fusogenic stage, we determined the structure of the virus at gradually lower pH values. The results show that while the fusion loop is available for external interaction and the shell and stalk domains of the spike begin to deteriorate, the E1 and E2 remain in close contact in the spike head. This unexpected observation points to E1 and E2 cooperation beyond the fusion loop exposure stage and implies a more prominent role for E2 in guiding membrane close encounter than has been earlier anticipated.
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Affiliation(s)
- Shang-Rung Wu
- Department of Biosciences and Nutrition, Karolinska Institutet, S-141 57 Huddinge, Sweden.
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25
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Nagata LP, Hu WG, Parker M, Chau D, Rayner GA, Schmaltz FL, Wong JP. Infectivity variation and genetic diversity among strains of Western equine encephalitis virus. J Gen Virol 2006; 87:2353-2361. [PMID: 16847131 DOI: 10.1099/vir.0.81815-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Variation in infectivity and genetic diversity in the structural proteins were compared among eight strains of Western equine encephalitis virus (WEEV) to investigate WEEV virulence at the molecular level. A lethal intranasal infectivity model of WEEV was developed in adult BALB/c mice. All eight strains examined were 100 % lethal to adult mice in this model, but they varied considerably in the time to death. Based on the time to death, the eight strains could be classified into two pathotypes: a high-virulence pathotype, consisting of strains California, Fleming and McMillan, and a low-virulence pathotype, comprising strains CBA87, Mn548, B11, Mn520 and 71V-1658. To analyse genetic diversity in the structural protein genes, 26S RNAs from these eight strains were cloned and sequenced and found to have > 96 % nucleotide and amino acid identity. A cluster diagram divided the eight WEEV strains into two genotypes that matched the pathotype grouping exactly, suggesting that variation in infectivity can be attributed to genetic diversity in the structural proteins among these eight strains. Furthermore, potential amino acid differences in some positions between the two groups were identified, suggesting that these amino acid variations contributed to the observed differences in virulence.
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MESH Headings
- Amino Acid Sequence
- Amino Acid Substitution
- Animals
- Cloning, Molecular
- Cluster Analysis
- Disease Models, Animal
- Encephalitis Virus, Western Equine/classification
- Encephalitis Virus, Western Equine/genetics
- Encephalitis Virus, Western Equine/pathogenicity
- Encephalomyelitis, Equine/virology
- Female
- Genetic Variation
- Genome, Viral
- Genotype
- Mice
- Mice, Inbred BALB C
- Molecular Sequence Data
- Phylogeny
- RNA, Viral/genetics
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Sequence Homology, Nucleic Acid
- Survival Analysis
- Time Factors
- Viral Structural Proteins/genetics
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Affiliation(s)
- Les P Nagata
- Chemical and Biological Defence Section, Defence Research and Development Canada - Suffield, Box 4000, Station Main, Medicine Hat, AB T1A 8K6, Canada
| | - Wei-Gang Hu
- Chemical and Biological Defence Section, Defence Research and Development Canada - Suffield, Box 4000, Station Main, Medicine Hat, AB T1A 8K6, Canada
| | - Michael Parker
- United States Army Medical Research Institute of Infectious Diseases, Frederick, MD 21702, USA
| | - Damon Chau
- Chemical and Biological Defence Section, Defence Research and Development Canada - Suffield, Box 4000, Station Main, Medicine Hat, AB T1A 8K6, Canada
| | - George A Rayner
- Chemical and Biological Defence Section, Defence Research and Development Canada - Suffield, Box 4000, Station Main, Medicine Hat, AB T1A 8K6, Canada
| | - Fay L Schmaltz
- Chemical and Biological Defence Section, Defence Research and Development Canada - Suffield, Box 4000, Station Main, Medicine Hat, AB T1A 8K6, Canada
| | - Jonathan P Wong
- Chemical and Biological Defence Section, Defence Research and Development Canada - Suffield, Box 4000, Station Main, Medicine Hat, AB T1A 8K6, Canada
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26
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Abstract
Alphaviruses are small highly ordered enveloped RNA viruses, which replicate very efficiently in the infected cell. They consist of a nucleocapsid (NC) and a surrounding membrane with glycoproteins. In the NC the positive single stranded RNA genome of the virus is enclosed by a T=4 icosahedral shell of capsid (C) proteins. The glycoproteins form a second shell with corresponding symmetry on the outside of the lipid membrane. These viruses mature by budding at the plasma membrane (PM) of the infected cell and enter into new cells by acid-triggered membrane fusion in endosomes. The viral glycoprotein consists of two subunits, E1, which carries the membrane fusion function, and E2, which suppresses this function until acid activation occurs. In the infected cell the RNA replication and transcription are confined to the cytoplasmic surface of endosome-derived vesicles called cytopathic vacuoles type I (CPV I). These structures are closely associated with membranes of the endoplasmic reticulum (ER), thereby creating a microenvironment for synthesis of viral proteins, assembly of the glycoproteins and formation of genome-C complexes. The budding process of the virus is initiated by C-glycoprotein interactions, possibly already before the glycoproteins arrive at the PM. This might involve a premade, ordered NC or a less ordered form of the genome-C complex. In the latter case, the interactions in the glycoprotein shell provide the major driving force for budding. The nature of the C-glycoprotein interaction has been resolved at atomic resolution by modelling. It involves hydrophobic interactions between a Tyr-X-Leu tripeptide in the internal tail of the E2 subunit and a pocket on the surface of the C protein. When the virus enters the endosome of a new cell the acid conditions trigger rearrangements in the glycoprotein shell, which result in the dissociation of the interactions that drive budding and a concomitant activation of the membrane fusion function in the E1 subunit.
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Affiliation(s)
- Henrik Garoff
- Department of Biosciences at Novum, Karolinska Institute, S-141 57 Huddinge, Sweden.
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27
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Abstract
A number of positive and negative strand RNA viruses whose primary site of replication is the cytoplasm use the nucleus and/or nuclear components in order to facilitate their replicative processes and alter host cell function. The nucleus itself is divided into a number of different sub-domains including structures such as the nucleolus. Many of the nuclear proteins that localise to these domains are involved in RNA processing, and because of their limited coding capacity, it may be necessary for RNA viruses to sequester such cellular factors in order to facilitate the replication, transcription and translation of their genomes. Amongst the best-studied examples of this are the picornaviruses, whose infection results in the redistribution of nuclear proteins to the cytoplasm and their interaction with the internal ribosome entry site (IRES) to facilitate translation of the picornavirus polyprotein. Examples can be found of other positive and also negative strand RNA virus proteins that localise to the nucleus and sub-domains (especially the nucleolus) during virus infection, and several localisation motifs have been defined. Apart from sequestering nuclear proteins for a role in replication, such viruses may also target the nucleus to disrupt nuclear functions and to inhibit antiviral responses.
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Affiliation(s)
- Julian A Hiscox
- School of Biochemistry and Molecular Biology, University of Leeds, LS2 9JT Leeds, UK.
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28
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Salonen A, Vasiljeva L, Merits A, Magden J, Jokitalo E, Kääriäinen L. Properly folded nonstructural polyprotein directs the semliki forest virus replication complex to the endosomal compartment. J Virol 2003; 77:1691-702. [PMID: 12525603 PMCID: PMC140886 DOI: 10.1128/jvi.77.3.1691-1702.2003] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The late RNA synthesis in alphavirus-infected cells, generating plus-strand RNAs, takes place on cytoplasmic vacuoles (CPVs), which are modified endosomes and lysosomes. The cytosolic surface of CPVs consists of regular membrane invaginations or spherules, which are the sites of RNA synthesis (P. Kujala, A. Ikäheimonen, N. Ehsani, H. Vihinen, P. Auvinen, and L. Kääriäinen J. Virol. 75:3873-3884, 2001). To understand how CPVs arise, we have expressed the individual Semliki Forest virus (SFV) nonstructural proteins nsP1 to nsP4 in different combinations, as well as their precursor polyprotein P1234 and its cleavage intermediates. A complex of nsPs was obtained from P123 or P1234, indicating that the precursor stage is essential for the assembly of the polymerase complex. To prevent the processing of the polyprotein and its cleavage intermediates, constructs with the mutation C478A (designated with a superscript CA) in the active site of the protease domain of nsP2 were used. Uncleaved polyproteins containing nsP1 were membrane bound and palmitoylated, and those containing nsP3 were phosphorylated, reflecting properties of authentic nsP1 and nsP3, respectively. Similarly, polyproteins containing nsP1 or nsP2 had enzymatic activities specific for the individual proteins, indicating that they were correctly folded in the precursor state. Uncleaved P12(CA) was localized almost exclusively to the plasma membrane and filopodia, like nsP1 alone, whereas P12(CA)3 and P12(CA)34 were found on cytoplasmic vesicles, some of which contained late endosomal markers. In immunoelectron microscopy these vesicles resembled CPVs in SFV-infected cells. Our results indicate that the nsP1 domain alone is responsible for the membrane association of the nonstructural polyprotein, whereas the nsP1 domain together with the nsP3 domain targets it to the intracellular vesicles.
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Affiliation(s)
- Anne Salonen
- Program in Cellular Biotechnology, Institute of Biotechnology, Biocenter Viikki, University of Helsinki, Helsinki, Finland
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29
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Wengler G, Wengler G. In vitro analysis of factors involved in the disassembly of Sindbis virus cores by 60S ribosomal subunits identifies a possible role of low pH. J Gen Virol 2002; 83:2417-2426. [PMID: 12237423 DOI: 10.1099/0022-1317-83-10-2417] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Disassembly of alphavirus cores early in infection involves interaction of the core with 60S ribosomal subunits. This interaction might be subjected to regulatory processes. We have established an in vitro system of core disassembly in order to identify cellular proteins involved in the regulation of disassembly. No evidence for the existence of such proteins was found, but it became apparent that certain organic solvents and detergents or a high proton concentration (pH 6.0) stimulated core disassembly. Alphaviruses infect cells by an endosomal pathway. The low pH in the endosome activates a fusion activity of the viral surface protein E1 and leads to fusion of the viral membrane with the endosomal membrane, followed by release of the core into the cytoplasm. Since the presence of the E1 protein in the plasma membrane of infected cells leads to increased membrane permeability at low pH, our findings indicate that disassembly of alphavirus cores could be regulated by the proton concentration. We propose that the viral membrane proteins present in the endosomal membrane after fusion form a pore, which allows the flow of protons from the endosome into the cytoplasm. This process would generate a region of low pH in the cytoplasm at the correct time and place to allow the efficient disassembly of the incoming viral core by 60S subunits.
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Affiliation(s)
- Gerd Wengler
- Institut für Virologie der Veterinärmedizin, Justus-Liebig-Universität Giessen, 35392 Giessen, Germany1
| | - Gisela Wengler
- Institut für Virologie der Veterinärmedizin, Justus-Liebig-Universität Giessen, 35392 Giessen, Germany1
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30
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Tellinghuisen TL, Perera R, Kuhn RJ. Genetic and biochemical studies on the assembly of an enveloped virus. GENETIC ENGINEERING 2002; 23:83-112. [PMID: 11570108 DOI: 10.1007/0-306-47572-3_6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Affiliation(s)
- T L Tellinghuisen
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
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31
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Gaspar LP, Terezan AF, Pinheiro AS, Foguel D, Rebello MA, Silva JL. The metastable state of nucleocapsids of enveloped viruses as probed by high hydrostatic pressure. J Biol Chem 2001; 276:7415-21. [PMID: 11092899 DOI: 10.1074/jbc.m010037200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Enveloped viruses fuse their membranes with cellular membranes to transfer their genomes into cells at the beginning of infection. What is not clear, however, is the role of the envelope (lipid bilayer and glycoproteins) in the stability of the viral particle. To address this question, we compared the stability between enveloped and nucleocapsid particles of the alphavirus Mayaro using hydrostatic pressure and urea. The effects were monitored by intrinsic fluorescence, light scattering, and binding of fluorescent dyes, including bis(8-anilinonaphthalene-1-sulfonate) and ethidium bromide. Pressure caused a drastic dissociation of the nucleocapsids as determined by tryptophan fluorescence, light scattering, and gel filtration chromatography. Pressure-induced dissociation of the nucleocapsids was poorly reversible. In contrast, when the envelope was present, pressure effects were much less marked and were highly reversible. Binding of ethidium bromide occurred when nucleocapsids were dissociated under pressure, indicating exposure of the nucleic acid, whereas enveloped particles underwent no changes. Overall, our results demonstrate that removal of the envelope with the glycoproteins leads the particle to a metastable state and, during infection, may serve as the trigger for disassembly and delivery of the genome. The envelope acts as a "Trojan horse," gaining entry into the host cell to allow release of a metastable nucleocapsid prone to disassembly.
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Affiliation(s)
- L P Gaspar
- Programa de Biologia Estrutural, Departamento de Bioquimica Médica, Instituto de Ciências Biomédicas, Centro Nacional de Ressonância Magnética Nuclear de Macromoléculas, Universidade Federal do Rio de Janeiro, 21941-590, RJ, Brazil
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32
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Perera R, Owen KE, Tellinghuisen TL, Gorbalenya AE, Kuhn RJ. Alphavirus nucleocapsid protein contains a putative coiled coil alpha-helix important for core assembly. J Virol 2001; 75:1-10. [PMID: 11119567 PMCID: PMC113891 DOI: 10.1128/jvi.75.1.1-10.2001] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The alphavirus nucleocapsid core is formed through the energetic contributions of multiple noncovalent interactions mediated by the capsid protein. This protein consists of a poorly conserved N-terminal region of unknown function and a C-terminal conserved autoprotease domain with a major role in virion formation. In this study, an 18-amino-acid conserved region, predicted to fold into an alpha-helix (helix I) and embedded in a low-complexity sequence enriched with basic and Pro residues, has been identified in the N-terminal region of the alphavirus capsid proteins. In Sindbis virus, helix I spans residues 38 to 55 and contains three conserved leucine residues, L38, L45, and L52, conforming to the heptad amino acid organization evident in leucine zipper proteins. Helix I consists of an N-terminally truncated heptad and two complete heptad repeats with beta-branched residues and conserved leucine residues occupying the a and d positions of the helix, respectively. Complete or partial deletion of helix I, or single-site substitutions at the conserved leucine residues (L45 and L52), caused a significant decrease in virus replication. The mutant viruses were more sensitive to elevated temperature than wild-type virus. These mutant viruses also failed to accumulate cores in the cytoplasm of infected cells, although they did not have defects in protein translation or processing. Analysis of these mutants using an in vitro assembly system indicated that the majority were defective in core particle assembly. Furthermore, mutant proteins showed a trans-dominant negative phenotype in in vitro assembly reactions involving mutant and wild-type proteins. We propose that helix I plays a central role in the assembly of nucleocapsid cores through coiled coil interactions. These interactions may stabilize subviral intermediates formed through the interactions of the C-terminal domain of the capsid protein and the genomic RNA and contribute to the stability of the virion.
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Affiliation(s)
- R Perera
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
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33
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Hiscox JA, Wurm T, Wilson L, Britton P, Cavanagh D, Brooks G. The coronavirus infectious bronchitis virus nucleoprotein localizes to the nucleolus. J Virol 2001; 75:506-12. [PMID: 11119619 PMCID: PMC113943 DOI: 10.1128/jvi.75.1.506-512.2001] [Citation(s) in RCA: 160] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2000] [Accepted: 10/02/2000] [Indexed: 11/20/2022] Open
Abstract
The coronavirus nucleoprotein (N) has been reported to be involved in various aspects of virus replication. We examined by confocal microscopy the subcellular localization of the avian infectious bronchitis virus N protein both in the absence and in the context of an infected cell and found that N protein localizes both to the cytoplasmic and nucleolar compartments.
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Affiliation(s)
- J A Hiscox
- School of Animal and Microbial Sciences, University of Reading, Reading, Berkshire RG6 6AJ, United Kingdom.
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34
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Forsell K, Xing L, Kozlovska T, Cheng RH, Garoff H. Membrane proteins organize a symmetrical virus. EMBO J 2000; 19:5081-91. [PMID: 11013211 PMCID: PMC302099 DOI: 10.1093/emboj/19.19.5081] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2000] [Revised: 08/03/2000] [Accepted: 08/10/2000] [Indexed: 01/13/2023] Open
Abstract
Alphaviruses are enveloped icosahedral viruses that mature by budding at the plasma membrane. According to a prevailing model maturation is driven by binding of membrane protein spikes to a preformed nucleocapsid (NC). The T = 4 geometry of the membrane is thought to be imposed by the NC through one-to-one interactions between spike protomers and capsid proteins (CPs). This model is challenged here by a Semliki Forest virus capsid gene mutant. Its CPs cannot assemble into NCs, or its intermediate structures, due to defective CP-CP interactions. Nevertheless, it can use its horizontal spike-spike interactions on membrane surface and vertical spike-CP interactions to make a particle with correct geometry and protein stoichiometry. Thus, our results highlight the direct role of membrane proteins in organizing the icosahedral conformation of alphaviruses.
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Affiliation(s)
- K Forsell
- Karolinska Institute, Department of Biosciences at Novum, S-141 57 Huddinge, Sweden
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35
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Tellinghuisen TL, Kuhn RJ. Nucleic acid-dependent cross-linking of the nucleocapsid protein of Sindbis virus. J Virol 2000; 74:4302-9. [PMID: 10756045 PMCID: PMC111947 DOI: 10.1128/jvi.74.9.4302-4309.2000] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The assembly of the alphavirus nucleocapsid core is a multistep event requiring the association of the nucleocapsid protein with nucleic acid and the subsequent oligomerization of capsid proteins into an assembled core particle. Although the mechanism of assembly has been investigated extensively both in vivo and in vitro, no intermediates in the core assembly pathway have been identified. Through the use of both truncated and mutant Sindbis virus nucleocapsid proteins and a variety of cross-linking reagents, a possible nucleic acid-protein assembly intermediate has been detected. The cross-linked species, a covalent dimer, has been detected only in the presence of nucleic acid and with capsid proteins capable of binding nucleic acid. Optimum nucleic acid-dependent cross-linking was seen at a protein-to-nucleic-acid ratio identical to that required for maximum binding of the capsid protein to nucleic acid. Identical results were observed when cross-linking in vitro assembled core particles of both Sindbis and Ross River viruses. Purified cross-linked dimers of truncated proteins and of mutant proteins that failed to assemble were found to incorporate into assembled core particles when present as minor components in assembly reactions, suggesting that the cross-linking traps an authentic intermediate in nucleocapsid core assembly. Endoproteinase Lys-C mapping of the position of the cross-link indicated that lysine 250 of one capsid protein was cross-linked to lysine 250 of an adjacent capsid protein. Examination of the position of the cross-link in relation to the existing model of the nucleocapsid core suggests that the cross-linked species is a cross-capsomere contact between a pentamer and hexamer at the quasi-threefold axis or is a cross-capsomere contact between hexamers at the threefold axis of the icosahedral core particle and suggests several possible assembly models involving a nucleic acid-bound dimer of capsid protein as an early step in the assembly pathway.
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Affiliation(s)
- T L Tellinghuisen
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
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36
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Villoing S, Béarzotti M, Chilmonczyk S, Castric J, Brémont M. Rainbow trout sleeping disease virus is an atypical alphavirus. J Virol 2000; 74:173-83. [PMID: 10590104 PMCID: PMC111526 DOI: 10.1128/jvi.74.1.173-183.2000] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sleeping disease (SD) is currently a matter of concern for salmonid fish farmers in most parts of the world. A viral etiology of SD has recently been suspected, since virus-like particles have been observed in infected rainbow trout cells. In salmonid-derived cell lines, the maximal rate of virus production was observed at 10 degrees C, while little virus was produced at 14 degrees C. Through biochemical, physicochemical, and morphological studies, SD virus (SDV) was shown to be an enveloped virus of roughly 60 nm in diameter. The genome consists of 12 kb of RNA, with the appearance of a 26S subgenomic RNA during the time course of SDV replication. The screening of a random-primed cDNA library constructed from the genomic RNA of semipurified virions facilitated the identification of a specific SDV cDNA clone having an open reading frame related to the alphavirus E2 glycoproteins. To extend the comparison between SDV structural proteins and the alphavirus protein counterparts, the nucleotide sequence of the total 4.1-kb subgenomic RNA has been determined. The 26S RNA encodes a 1,324-amino-acid polyprotein exhibiting typical alphavirus structural protein organization. SDV structural proteins showed several remarkable features compared to other alphaviruses: (i) unusually large individual proteins, (ii) very low homology (ranging from 30 to 34%) (iii) an unglycosylated E3 protein, and (iv) and E1 fusion domain sharing mutations implicated in the pH threshold. Although phylogenetically related to the Semliki Forest virus group of alphaviruses, SDV should be considered an atypical member, able to naturally replicate in lower vertebrates.
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Affiliation(s)
- S Villoing
- Unité de Virologie et Immunologie Moléculaires, Institut National de la Recherche Agronomique, 78352 Jouy-en-Josas Cedex, France
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37
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Tellinghuisen TL, Hamburger AE, Fisher BR, Ostendorp R, Kuhn RJ. In vitro assembly of alphavirus cores by using nucleocapsid protein expressed in Escherichia coli. J Virol 1999; 73:5309-19. [PMID: 10364277 PMCID: PMC112586 DOI: 10.1128/jvi.73.7.5309-5319.1999] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The production of the alphavirus virion is a multistep event requiring the assembly of the nucleocapsid core in the cytoplasm and the maturation of the glycoproteins in the endoplasmic reticulum and the Golgi apparatus. These components associate during the budding process to produce the mature virion. The nucleocapsid proteins of Sindbis virus and Ross River virus have been produced in a T7-based Escherichia coli expression system and purified. In the presence of single-stranded but not double-stranded nucleic acid, the proteins oligomerize in vitro into core-like particles which resemble the native viral nucleocapsid cores. Despite their similarities, Sindbis virus and Ross River virus capsid proteins do not form mixed core-like particles. Truncated forms of the Sindbis capsid protein were used to establish amino acid requirements for assembly. A capsid protein starting at residue 19 [CP(19-264)] was fully competent for in vitro assembly, whereas proteins with further N-terminal truncations could not support assembly. However, a capsid protein starting at residue 32 or 81 was able to incorporate into particles in the presence of CP(19-264) or could inhibit assembly if its molar ratio relative to CP(19-264) was greater than 1:1. This system provides a basis for the molecular dissection of alphavirus core assembly.
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Affiliation(s)
- T L Tellinghuisen
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
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38
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Wengler G, Wengler G, Rey FA. The isolation of the ectodomain of the alphavirus E1 protein as a soluble hemagglutinin and its crystallization. Virology 1999; 257:472-82. [PMID: 10329557 DOI: 10.1006/viro.1999.9661] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Alphaviruses are isometric enveloped viruses approximately 70 nm in diameter. The viral surface contains 80 glycoprotein spikes arranged in a T = 4 lattice. Each of these spikes consists of three heterodimers of the viral membrane proteins E1 (approximately 49 kDa) and E2 (approximately 51 kDa). Cryoelectron microscopic analyses have shown that the spikes form a protein shell on the viral surface. We have made an attempt to isolate biologically active protein fragments from this surface and to grow crystals from such fragments. To this end membrane proteins were extracted with Nonidet-P40 from the Semliki Forest alphavirus and the proteins were separated from detergent by centrifugation. A protein complex containing the E1 and E2 molecules in quantitative yield was obtained by this procedure. This complex has the following properties: It sediments at approximately 30S, it chromatographs with an apparent molecular mass of approximately 580,000 Da during gel filtration, it cannot be dissociated by either nonionic detergents or 6 M urea, and at acid pH it is a highly active hemagglutinin. The data indicate that this 30S hemagglutinin complex, which has not been hitherto described for alphaviruses, may represent a variant form of the protein lattice present on the alphavirus surface. Cleavage of this complex by subtilisin selectively removes carboxy-terminal sequences from the E1 and E2 proteins, which contain the cytoplasmic and transmembrane segments of the proteins and a small part of their ectodomain. The remaining ectodomains are called E1DeltaS and E2DeltaS. This proteolysis also leads to dissociation of the 30S complex. The cleavage products accumulate in the form of a heterodimer of the E1DeltaS and E2DeltaS proteins. Treatment of the heterodimer with PNGase F leads to rapid removal of carbohydrate from the E2DeltaS protein and a dissociation of the complex into the constituent molecules, which can be separated by chromatography. The finding that the heterodimer and the purified E1DeltaS protein both function as hemagglutinin at acid pH indicates that the E1 protein represents the alphavirus hemagglutinin. We have obtained crystals of the E1DeltaS protein and are currently in the process of determining the atomic structure of this protein by the isomorphous replacement method.
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Affiliation(s)
- G Wengler
- Institut für Virologie, Justus-Liebig-Universität Giessen, Giessen, 35392, Germany
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39
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Abstract
The ability of viruses to transfer macromolecules between cells makes them attractive starting points for the design of biological delivery vehicles. Virus-based vectors and sub-viral systems are already finding biotechnological and medical applications for gene, peptide, vaccine and drug delivery. Progress has been made in understanding the cellular and molecular mechanisms underlying virus entry, particularly in identifying virus receptors. However, receptor binding is only a first step and we now have to understand how these molecules facilitate entry, how enveloped viruses fuse with cells or non-enveloped viruses penetrate the cell membrane, and what happens following penetration. Only through these detailed analyses will the full potential of viruses as vectors and delivery vehicles be realised. Here we discuss aspects of the entry mechanisms for several well-characterised viral systems. We do not attempt to provide a fully comprehensive review of virus entry but focus primarily on enveloped viruses.
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Affiliation(s)
| | | | - Mark Marsh
- Corresponding author. Tel.: +44 171 380 7807; fax: +44 171 380 7805; e-mail
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40
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Abstract
Viruses are efficient carriers of genetic material between cells. They specifically recognise a target cell and utilise host functions for genome delivery to the replication site. A mature viral capsid emerging from an infected cell serves at least three distinct functions. It enables virus egress from the infected cell, protects the extracellular genome against chemical and physical stress and mediates virus entry into a non-infected cell. How can a virus particle be stably assembled in an infected cell and moments later-after passing through the extracellular milieu-be disintegrated by a non-infected cell? In this review I discuss how adenovirus, a DNA virus, recruits cellular and viral factors and makes use of its own cysteine protease to regulate capsid assembly and disassembly. Copyright 1998 John Wiley & Sons, Ltd.
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Affiliation(s)
- UF Greber
- Institute of Zoology, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
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41
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Seabaugh RC, Olson KE, Higgs S, Carlson JO, Beaty BJ. Development of a chimeric sindbis virus with enhanced per Os infection of Aedes aegypti. Virology 1998; 243:99-112. [PMID: 9527919 DOI: 10.1006/viro.1998.9034] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The TE/3'2J double subgenomic Sindbis (dsSIN) viruses have been used to stably express genes in Aedes aegypti nerve and salivary gland tissues. However, because these viruses inefficiently infect Ae. aegypti when administered by the per os route, TE/3'2J viruses must be intrathoracically inoculated into the mosquitoes to infect these tissues. A Malaysian Sindbis (SIN) virus isolate (MRE16) does efficiently infect Ae. aegypti midgut tissues after ingestion, and approximately 95% of these mosquitoes also develop disseminated infections within 14 days. We have sequenced the entire 26S RNA of MRE16 virus and have developed a chimeric SIN cDNA infectious clone, designated MRE1001, which contains sequence elements of TE/3'2J and MRE16 virus. MRE1001 virus efficiently infects midgut cells, and greater than 90% of infected mosquitoes develop disseminated infections after 14 days extrinsic incubation. The chimeric MRE1001 cDNA clone should allow identification of viral determinants of midgut infection and dissemination and lead to the development of new SIN virus expression systems.
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Affiliation(s)
- R C Seabaugh
- Department of Microbiology, Colorado State University, Fort Collins 80523, USA
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42
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Abstract
Intact, purified particles of the nodaviruses flock house virus and nodamura virus that were either transfected into cells that were resistant to infection or introduced into in vitro translation systems directed the synthesis of viral proteins. We infer that direct interaction of these nodavirus particles with cytoplasmic components mediated virion disassembly that resulted in release of the viral RNA.
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Affiliation(s)
- J A Hiscox
- Department of Microbiology, University of Alabama at Birmingham, 35294-2170, USA
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43
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Abstract
According to the present model for assembly of alphaviruses, e.g. Semliki Forest virus (SFV), the viral genome is first encapsidated into a nucleocapsid (NC) in cytoplasm and this is then used for budding at plasma membrane (PM). The preformed NC is thought to act as a template on which the viral envelope can be organized. In the present work we have characterized two SFV deletion mutants which did not assemble NCs in the cytoplasm but which instead appeared to form NCs at the PM simultaneously with virus budding. The deletions were introduced in a conserved 14 residue long linker peptide that joins the amino-terminal RNA-binding domain with the carboxy-terminal serine-protease domain of the capsid protein. Despite the deletions and the change in morphogenesis, wild-type (wt)-like particles were produced with almost wt efficiency. It is suggested that the NC assembly defect of the mutants is rescued through spike-capsid interactions at PM. The results show that the preassembly of NCs in the cytoplasm is not a prerequisite for alphavirus budding. The apparent similarities of the morphogenesis pathways of wt and mutant SFV with those of type D and type C retroviruses are discussed.
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Affiliation(s)
- K Forsell
- Department of Bioscience at Novum, Huddinge, Sweden
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44
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Marsh M, Bron R. SFV infection in CHO cells: cell-type specific restrictions to productive virus entry at the cell surface. J Cell Sci 1997; 110 ( Pt 1):95-103. [PMID: 9010788 DOI: 10.1242/jcs.110.1.95] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Alphaviruses, such as Semliki Forest virus, normally enter cells by penetration from acidic organelles of the endocytic pathway. The virions are internalised intact from the cell surface before undergoing acid-induced fusion in endosomes. To investigate the possibility that endocytosis might play a role in delivering virions to specific sites for replication, we compared SFV infection of baby hamster kidney (BHK) cells and Chinese hamster ovary (CHO) cells following either normal virus fusion in endosomes or experimentally-induced fusion at the cell surface. Whereas baby hamster kidney cells were infected efficiently following fusion in endosomes or at the plasma membrane, Chinese hamster ovary cells were only infected following fusion from endocytic organelles. Virions fused at the plasma membrane of CHO cells failed to initiate viral RNA and protein synthesis. Similar results were observed when CHO cells were challenged with a rhabdovirus, vesicular stomatitis virus. These data suggest that in certain cell types a barrier, other than the plasma membrane, can prevent infection by alpha- and rhabdoviruses fused at the cell surface. Moreover, they suggest the endocytic pathway provides a mechanism for bringing viral particles to a site, or sites, in the cell where replication can proceed.
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Affiliation(s)
- M Marsh
- MRC Laboratory for Molecular Cell Biology, University College London, UK.
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45
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Kuhn RJ, Griffin DE, Owen KE, Niesters HG, Strauss JH. Chimeric Sindbis-Ross River viruses to study interactions between alphavirus nonstructural and structural regions. J Virol 1996; 70:7900-9. [PMID: 8892913 PMCID: PMC190862 DOI: 10.1128/jvi.70.11.7900-7909.1996] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Sindbis virus and Ross River virus are alphaviruses whose nonstructural proteins share 64% identity and whose structural proteins share 48% identity. Starting from full-length cDNA clones of both viruses, we have generated two reciprocal Sindbis-Ross River chimeric viruses in which the structural and nonstructural regions have been exchanged. These chimeric viruses replicate readily in several cell lines. Both chimeras grow more poorly than do the parental viruses, with the chimera containing Sindbis virus nonstructural proteins and Ross River virus structural proteins growing considerably better in both mosquito and Vero cell lines than the reciprocal chimera does. The reduction in replicative capacity in comparison with the parental viruses appears to result at least in part from a reduction in RNA synthesis, which suggests that the structural proteins or sequence elements within the structural region interact with the nonstructural proteins or sequence elements within the nonstructural region, that these interactions are required for efficient RNA replication, and that these interactions are suboptimal in the chimeras. The chimeras are able to infect mice, but their growth is attenuated. Western equine encephalitis virus, a virus widely distributed throughout the Americas, has been previously shown to have arisen by natural recombination between two distinct alphaviruses, but other naturally occurring recombinant alphaviruses have not been found. The present results suggest that most nonstructural/structural chimeras that might arise by natural recombination will be viable but that interactions between different regions of the genome, some of which were previously known but some of which remain unknown, limit the ability of such recombinants to become established.
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Affiliation(s)
- R J Kuhn
- Division of Biology, California Institute of Technology, Pasadena 91125, USA
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46
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Mrkic B, Kempf C. The fragmentation of incoming Semliki Forest virus nucleocapsids in mosquito (Aedes albopictus) cells might be coupled to virion uncoating. Arch Virol 1996; 141:1805-21. [PMID: 8920817 DOI: 10.1007/bf01718196] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The fate of Semliki Forest virus (SFV) nucleocapsid, especially the capsid protein (C-protein), was investigated during the early stages of a productive infection in mosquito Aedes albopictus cells. Infection of the cells resulted in a time dependent accumulation of a C-protein derived fragment. This fragmentation of incoming viral nucleocapsid was prevented by NH4Cl, an agent generally used to elevate the pH in acidic intracellular compartments, suggesting that a low intravesicular pH is required for this process. Density gradient analysis of the postnuclear cell lysate demonstrated that the fragmentation was associated with a cellular compartment showing a density of 1.14 +/- 0.02 g/ml. This cellular compartment was devoid from a lysosomal marker enzyme and represented the timely preceding cellular fraction through which SFV passed before encountering a lysosomal fraction. Furthermore, the intracellular distribution of the viral, 3H-uridine-labeled RNA suggested that the same fraction might represent a key cellular compartment in which the separation of the viral RNA from the viral structural proteins is primed. In conclusion, these data lead to the suggestion that the fragmentation of incoming SFV nucleocapsids in Aedes albopictus cells might be the part of the mechanism leading to the release of viral RNA into the cytosol during early stages of productive infection.
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Affiliation(s)
- B Mrkic
- Institute of Biochemistry, University of Bern, Switzerland
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47
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Lee S, Owen KE, Choi HK, Lee H, Lu G, Wengler G, Brown DT, Rossmann MG, Kuhn RJ. Identification of a protein binding site on the surface of the alphavirus nucleocapsid and its implication in virus assembly. Structure 1996; 4:531-41. [PMID: 8736552 DOI: 10.1016/s0969-2126(96)00059-7] [Citation(s) in RCA: 138] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Many enveloped viruses exit cells by budding from the plasma membrane. The driving force for budding is the interaction of an inner protein nucleocapsid core with transmembrane glycoprotein spikes. The molecular details of this process are ill defined. Alphaviruses, such as Sindbis virus (SINV) and Semliki Forest virus (SFV), represent some of the simplest enveloped viruses and have been well characterized by structural, genetic and biochemical techniques. Although a high-resolution structure of an alphavirus has not yet been attained, cryo-electron microscopy (cryo-EM) has been used to show the multilayer organization at 25 A resolution. In addition, atomic resolution studies are available of the C-terminal domain of the nucleocapsid protein and this has been modeled into the cryo-EM density. RESULTS A recombinant form of Sindbis virus core protein (SCP) was crystallized and found to diffract much better than protein extracted from the virus (2.0 A versus 3.0 A resolution). The new structure showed that amino acids 108 to 111 bind to a specific hydrophobic pocket in neighboring molecules. Re-examination of the structures derived from virus-extracted protein also showed this 'N-terminal arm' binding to the same hydrophobic pocked in adjacent molecules. It is proposed that the binding of these capsid residues into the hydrophobic pocket of SCP mimics the binding of E2 (one of two glycoproteins that penetrate the lipid bilayer of the viral envelope) C-terminal residues in the pocket. Mutational studies of capsid residues 108 and 110 confirm their role in capsid assembly. CONCLUSIONS Structural and mutational analyses of residues within the hydrophobic pocket suggest that budding results in a switch between two conformations of the capsid hydrophobic pocket. This is the first description of a viral budding mechanism in molecular detail.
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Affiliation(s)
- S Lee
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA
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48
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Owen KE, Kuhn RJ. Identification of a region in the Sindbis virus nucleocapsid protein that is involved in specificity of RNA encapsidation. J Virol 1996; 70:2757-63. [PMID: 8627749 PMCID: PMC190132 DOI: 10.1128/jvi.70.5.2757-2763.1996] [Citation(s) in RCA: 105] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The specific encapsidation of genomic RNA by an alphavirus requires recognition of the viral RNA by the nucleocapsid protein. In an effort to identify individual residues of the Sindbis virus nucleocapsid protein which are essential for this recognition event, a molecular genetic analysis of a domain of the protein previously suggested to be involved in RNA binding in vitro was undertaken. The experiments presented describe the generation of a panel of viruses which contain mutations in residues 97 through 111 of the nucleocapsid protein. All of the viruses generated were viable, and the results suggest that, individually, the residues mutated do not play a critical role in encapsidation. However, one mutant which had lost the ability to specifically encapsidate the genomic RNA was identified. This mutant virus, which contained a deletion of residues 97 to 106, encapsidated both the genomic RNA and the subgenomic mRNA of the virus. It is proposed that the encapsidation of this second species of RNA, which is not present in wild-type virions, is the result of the loss of a domain of the nucleocapsid protein required for specific recognition of the genomic RNA packaging signal. The results suggest that this region of the protein is important in dictating specificity in the encapsidation reaction in vivo. The isolation and preliminary characterization of two independent second-site revertants to this deletion mutant are also described.
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Affiliation(s)
- K E Owen
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
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49
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Forsell K, Suomalainen M, Garoff H. Structure-function relation of the NH2-terminal domain of the Semliki Forest virus capsid protein. J Virol 1995; 69:1556-63. [PMID: 7853489 PMCID: PMC188749 DOI: 10.1128/jvi.69.3.1556-1563.1995] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The capsid (C) protein of alphaviruses consists of two protein domains: a serine protease at the COOH terminus and an NH2-terminal domain which is thought to interact with RNA in the virus nucleocapsid (NC). The latter domain is very rich in positively charged amino acid residues. In this work, we have introduced large deletions into the corresponding region of a full-length cDNA clone of Semliki Forest virus, expressed the transcribed RNA in BHK-21 cells, and monitored the autoprotease activity of C, the formation of intracellular NCs, and the release of infectious virus. Our results show that if the gene region encoding the whole NH2-terminal domain is removed, the expressed C protein fragment cannot assemble into NCs and virus particles but it is still able to function as an autoprotease. Thus, these results underline the general importance of the NH2-terminal domain in the virus assembly process and furthermore show that the serine protease domain can function independently of the NH2 terminus. Surprisingly, analysis of additional C protein deletion variants showed that not all of the NH2-terminal domain is required for virus assembly, but large deletions involving up to one-third of its positively charged residues are still compatible with NC and virus formation. The fact that so much flexibility is allowed in the structure of the NH2-terminal domain of C suggests that most of this region is involved in nonspecific interactions with the encapsidated RNA, probably through its positively charged amino acid residues.
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Affiliation(s)
- K Forsell
- Center for Biotechnology, Karolinska Institute, Huddinge, Sweden
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50
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Cheng RH, Kuhn RJ, Olson NH, Rossmann MG, Choi HK, Smith TJ, Baker TS. Nucleocapsid and glycoprotein organization in an enveloped virus. Cell 1995; 80:621-30. [PMID: 7867069 PMCID: PMC4167723 DOI: 10.1016/0092-8674(95)90516-2] [Citation(s) in RCA: 254] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Alphaviruses are a group of icosahedral, positive-strand RNA, enveloped viruses. The membrane bilayer, which surrounds the approximately 400 A diameter nucleocapsid, is penetrated by 80 spikes arranged in a T = 4 lattice. Each spike is a trimer of heterodimers consisting of glycoproteins E1 and E2. Cryoelectron microscopy and image reconstruction of Ross River virus showed that the T = 4 quaternary structure of the nucleocapsid consists of pentamer and hexamer clusters of the capsid protein, but not dimers, as have been observed in several crystallographic studies. The E1-E2 heterodimers form one-to-one associations with the nucleocapsid monomers across the lipid bilayer. Knowledge of the atomic structure of the capsid protein and our reconstruction allows us to identify capsid-protein residues that interact with the RNA, the glycoproteins, and adjacent capsid-proteins.
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Affiliation(s)
- R H Cheng
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
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