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Hoffka G, Lountos GT, Needle D, Wlodawer A, Waugh DS, Tőzsér J, Mótyán JA. Self-inhibited State of Venezuelan Equine Encephalitis Virus (VEEV) nsP2 Cysteine Protease: A Crystallographic and Molecular Dynamics Analysis. J Mol Biol 2023; 435:168012. [PMID: 36792007 PMCID: PMC10758287 DOI: 10.1016/j.jmb.2023.168012] [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: 11/03/2022] [Revised: 02/06/2023] [Accepted: 02/07/2023] [Indexed: 02/15/2023]
Abstract
The Venezuelan equine encephalitis virus (VEEV) belongs to the Togaviridae family and is pathogenic to both humans and equines. The VEEV non-structural protein 2 (nsP2) is a cysteine protease (nsP2pro) that processes the polyprotein and thus it is a drug target for inhibitor discovery. The atomic structure of the VEEV nsP2 catalytic domain was previously characterized by both X-ray crystallography and computational studies. A modified nsP2pro harboring a N475A mutation in the N terminus was observed to exhibit an unexpected conformation: the N-terminal residues bind to the active site, mimicking binding of a substrate. The large conformational change of the N terminus was assumed to be induced by the N475A mutation, as N475 has an important role in stabilization of the N terminus and the active site. This conformation was first observed in the N475A mutant, but we also found it while determining a crystal structure of the catalytically active nsP2pro containing the wild-type N475 active site residue and K741A/K767A surface entropy reduction mutations. This suggests that the N475A mutation is not a prerequisite for self-inhibition. Here, we describe a high resolution (1.46 Å) crystal structure of a truncated nsP2pro (residues 463-785, K741A/K767A) and analyze the structure further by molecular dynamics to study the active and self-inhibited conformations of nsP2pro and its N475A mutant. A comparison of the different conformations of the N-terminal residues sheds a light on the interactions that play an important role in the stabilization of the enzyme.
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Affiliation(s)
- Gyula Hoffka
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Hungary; Doctoral School of Molecular Cell and Immune Biology, University of Debrecen, Debrecen, Hungary
| | - George T Lountos
- Basic Science Program, Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA
| | - Danielle Needle
- Center for Structural Biology, National Cancer Institute, Frederick, MD 21702, USA
| | - Alexander Wlodawer
- Center for Structural Biology, National Cancer Institute, Frederick, MD 21702, USA
| | - David S Waugh
- Center for Structural Biology, National Cancer Institute, Frederick, MD 21702, USA
| | - József Tőzsér
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Hungary
| | - János András Mótyán
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Hungary.
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2
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Varghese FS, Meutiawati F, Teppor M, Jacobs S, de Keyzer C, Taşköprü E, van Woudenbergh E, Overheul GJ, Bouma E, Smit JM, Delang L, Merits A, van Rij RP. Posaconazole inhibits multiple steps of the alphavirus replication cycle. Antiviral Res 2021; 197:105223. [PMID: 34856248 DOI: 10.1016/j.antiviral.2021.105223] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 11/22/2021] [Accepted: 11/27/2021] [Indexed: 11/28/2022]
Abstract
Repurposing drugs is a promising strategy to identify therapeutic interventions against novel and re-emerging viruses. Posaconazole is an antifungal drug used to treat invasive aspergillosis and candidiasis. Recently, posaconazole and its structural analog, itraconazole were shown to inhibit replication of multiple viruses by modifying intracellular cholesterol homeostasis. Here, we show that posaconazole inhibits replication of the alphaviruses Semliki Forest virus (SFV), Sindbis virus and chikungunya virus with EC50 values ranging from 1.4 μM to 9.5 μM. Posaconazole treatment led to a significant reduction of virus entry in an assay using a temperature-sensitive SFV mutant, but time-of-addition and RNA transfection assays indicated that posaconazole also inhibits post-entry stages of the viral replication cycle. Virus replication in the presence of posaconazole was partially rescued by the addition of exogenous cholesterol. A transferrin uptake assay revealed that posaconazole considerably slowed down cellular endocytosis. A single point mutation in the SFV E2 glycoprotein, H255R, provided partial resistance to posaconazole as well as to methyl-β-cyclodextrin, corroborating the effect of posaconazole on cholesterol and viral entry. Our results indicate that posaconazole inhibits multiple steps of the alphavirus replication cycle and broaden the spectrum of viruses that can be targeted in vitro by posaconazole, which could be further explored as a therapeutic agent against emerging viruses.
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Affiliation(s)
- Finny S Varghese
- Department of Medical Microbiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Febrina Meutiawati
- Department of Medical Microbiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Mona Teppor
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Sofie Jacobs
- KU Leuven, Department of Microbiology, Immunology and Transplantation, Rega Institute for Medical Research, Laboratory of Virology and Chemotherapy, Leuven, Belgium
| | - Carolien de Keyzer
- KU Leuven, Department of Microbiology, Immunology and Transplantation, Rega Institute for Medical Research, Laboratory of Virology and Chemotherapy, Leuven, Belgium
| | - Ezgi Taşköprü
- Department of Medical Microbiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Esther van Woudenbergh
- Section Pediatric Infectious Diseases, Laboratory of Medical Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, the Netherlands; Centre for Immunology of Infectious Diseases and Vaccines, National Institute for Public Health and the Environment, Bilthoven, the Netherlands
| | - Gijs J Overheul
- Department of Medical Microbiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Ellen Bouma
- Department of Medical Microbiology and Infection Prevention, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
| | - Jolanda M Smit
- Department of Medical Microbiology and Infection Prevention, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
| | - Leen Delang
- KU Leuven, Department of Microbiology, Immunology and Transplantation, Rega Institute for Medical Research, Laboratory of Virology and Chemotherapy, Leuven, Belgium
| | - Andres Merits
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Ronald P van Rij
- Department of Medical Microbiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, the Netherlands.
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Bozóki B, Mótyán JA, Hoffka G, Waugh DS, Tőzsér J. Specificity Studies of the Venezuelan Equine Encephalitis Virus Non-Structural Protein 2 Protease Using Recombinant Fluorescent Substrates. Int J Mol Sci 2020; 21:E7686. [PMID: 33081394 PMCID: PMC7593941 DOI: 10.3390/ijms21207686] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 10/13/2020] [Accepted: 10/14/2020] [Indexed: 11/16/2022] Open
Abstract
The non-structural protein 2 (nsP2) of alphavirus Venezuelan equine encephalitis virus (VEEV) is a cysteine protease that is responsible for processing of the viral non-structural polyprotein and is an important drug target owing to the clinical relevance of VEEV. In this study we designed two recombinant VEEV nsP2 constructs to study the effects of an N-terminal extension on the protease activity and to investigate the specificity of the elongated enzyme in vitro. The N-terminal extension was found to have no substantial effect on the protease activity. The amino acid preferences of the VEEV nsP2 protease were investigated on substrates representing wild-type and P5, P4, P2, P1, P1', and P2' variants of Semliki forest virus nsP1/nsP2 cleavage site, using a His6-MBP-mEYFP recombinant substrate-based protease assay which has been adapted for a 96-well plate-based format. The structural basis of enzyme specificity was also investigated in silico by analyzing a modeled structure of VEEV nsP2 complexed with oligopeptide substrate. To our knowledge, in vitro screening of P1' amino acid preferences of VEEV nsP2 protease remains undetermined to date, thus, our results may provide valuable information for studies and inhibitor design of different alphaviruses or other Group IV viruses.
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Affiliation(s)
- Beáta Bozóki
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (B.B.); (G.H.)
- Doctoral School of Molecular Cell and Immune Biology, University of Debrecen, 4032 Debrecen, Hungary
| | - János András Mótyán
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (B.B.); (G.H.)
| | - Gyula Hoffka
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (B.B.); (G.H.)
- Doctoral School of Molecular Cell and Immune Biology, University of Debrecen, 4032 Debrecen, Hungary
- MTA-DE Laboratory of Protein Dynamics, Department of Biochemistry and Molecular Biology, University of Debrecen, 4032 Debrecen, Hungary
| | - David S. Waugh
- Macromolecular Crystallography Laboratory, Center for Cancer Research, National Cancer Institute at Frederick, Frederick, MD 21702, USA;
| | - József Tőzsér
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (B.B.); (G.H.)
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4
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Pietilä MK, Hellström K, Ahola T. Alphavirus polymerase and RNA replication. Virus Res 2017; 234:44-57. [DOI: 10.1016/j.virusres.2017.01.007] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 01/05/2017] [Accepted: 01/09/2017] [Indexed: 10/20/2022]
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Obatoclax Inhibits Alphavirus Membrane Fusion by Neutralizing the Acidic Environment of Endocytic Compartments. Antimicrob Agents Chemother 2017; 61:AAC.02227-16. [PMID: 27993855 DOI: 10.1128/aac.02227-16] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Accepted: 12/14/2016] [Indexed: 12/11/2022] Open
Abstract
As new pathogenic viruses continue to emerge, it is paramount to have intervention strategies that target a common denominator in these pathogens. The fusion of viral and cellular membranes during viral entry is one such process that is used by many pathogenic viruses, including chikungunya virus, West Nile virus, and influenza virus. Obatoclax, a small-molecule antagonist of the Bcl-2 family of proteins, was previously determined to have activity against influenza A virus and also Sindbis virus. Here, we report it to be active against alphaviruses, like chikungunya virus (50% effective concentration [EC50] = 0.03 μM) and Semliki Forest virus (SFV; EC50 = 0.11 μM). Obatoclax inhibited viral entry processes in an SFV temperature-sensitive mutant entry assay. A neutral red retention assay revealed that obatoclax induces the rapid neutralization of the acidic environment of endolysosomal vesicles and thereby most likely inhibits viral fusion. Characterization of escape mutants revealed that the L369I mutation in the SFV E1 fusion protein was sufficient to confer partial resistance against obatoclax. Other inhibitors that target the Bcl-2 family of antiapoptotic proteins inhibited neither viral entry nor endolysosomal acidification, suggesting that the antiviral mechanism of obatoclax does not depend on its anticancer targets. Obatoclax inhibited the growth of flaviviruses, like Zika virus, West Nile virus, and yellow fever virus, which require low pH for fusion, but not that of pH-independent picornaviruses, like coxsackievirus A9, echovirus 6, and echovirus 7. In conclusion, obatoclax is a novel inhibitor of endosomal acidification that prevents viral fusion and that could be pursued as a potential broad-spectrum antiviral candidate.
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Balistreri G, Bognanni C, Mühlemann O. Virus Escape and Manipulation of Cellular Nonsense-Mediated mRNA Decay. Viruses 2017; 9:v9010024. [PMID: 28124995 PMCID: PMC5294993 DOI: 10.3390/v9010024] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Revised: 01/05/2017] [Accepted: 01/13/2017] [Indexed: 12/13/2022] Open
Abstract
Nonsense-mediated mRNA decay (NMD), a cellular RNA turnover pathway targeting RNAs with features resulting in aberrant translation termination, has recently been found to restrict the replication of positive-stranded RNA ((+)RNA) viruses. As for every other antiviral immune system, there is also evidence of viruses interfering with and modulating NMD to their own advantage. This review will discuss our current understanding of why and how NMD targets viral RNAs, and elaborate counter-defense strategies viruses utilize to escape NMD.
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Affiliation(s)
- Giuseppe Balistreri
- Department of Biosciences, University of Helsinki, Helsinki FIN-00014, Finland.
| | - Claudia Bognanni
- Department of Chemistry and Biochemistry, University of Bern, Bern CH-3012, Switzerland.
- Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern CH-3012, Switzerland.
| | - Oliver Mühlemann
- Department of Chemistry and Biochemistry, University of Bern, Bern CH-3012, Switzerland.
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Campos-Gomez J, Ahmad F, Rodriguez E, Saeed MF. A novel cell-based assay to measure activity of Venezuelan equine encephalitis virus nsP2 protease. Virology 2016; 496:77-89. [PMID: 27261892 DOI: 10.1016/j.virol.2016.05.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Revised: 04/06/2016] [Accepted: 05/16/2016] [Indexed: 11/26/2022]
Abstract
The encephalitic alphaviruses encode nsP2 protease (nsP2pro), which because of its vital role in virus replication, represents an attractive target for therapeutic intervention. To facilitate the discovery of nsP2 inhibitors we have developed a novel assay for quantitative measurement of nsP2pro activity in a cell-based format. The assay is based on a substrate fusion protein consisting of eGFP and Gaussia luciferase (Gluc) linked together by a small peptide containing a VEEV nsp2pro cleavage sequence. The expression of the substrate protein in cells along with recombinant nsP2pro results in cleavage of the substrate protein resulting in extracellular release of free Gluc. The Gluc activity in supernatants corresponds to intracellular nsP2pro-mediated substrate cleavage; thus, providing a simple and convenient way to quantify nsP2pro activity. Here, we demonstrate potential utility of the assay in identification of nsP2pro inhibitors, as well as in investigations related to molecular characterization of nsP2pro.
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Affiliation(s)
- Javier Campos-Gomez
- Department of Infectious Diseases, Drug Discovery Division, Southern Research, Birmingham, AL 35205, United States
| | - Fahim Ahmad
- Department of Infectious Diseases, Drug Discovery Division, Southern Research, Birmingham, AL 35205, United States
| | - Efrain Rodriguez
- Department of Infectious Diseases, Drug Discovery Division, Southern Research, Birmingham, AL 35205, United States
| | - Mohammad F Saeed
- Department of Infectious Diseases, Drug Discovery Division, Southern Research, Birmingham, AL 35205, United States.
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Balistreri G, Horvath P, Schweingruber C, Zünd D, McInerney G, Merits A, Mühlemann O, Azzalin C, Helenius A. The host nonsense-mediated mRNA decay pathway restricts Mammalian RNA virus replication. Cell Host Microbe 2015; 16:403-11. [PMID: 25211080 DOI: 10.1016/j.chom.2014.08.007] [Citation(s) in RCA: 122] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 07/29/2014] [Accepted: 08/19/2014] [Indexed: 01/05/2023]
Abstract
In addition to classically defined immune mechanisms, cell-intrinsic processes can restrict virus infection and have shaped virus evolution. The details of this virus-host interaction are still emerging. Following a genome-wide siRNA screen for host factors affecting replication of Semliki Forest virus (SFV), a positive-strand RNA (+RNA) virus, we found that depletion of nonsense-mediated mRNA decay (NMD) pathway components Upf1, Smg5, and Smg7 led to increased levels of viral proteins and RNA and higher titers of released virus. The inhibitory effect of NMD was stronger when virus replication efficiency was impaired by mutations or deletions in the replicase proteins. Consequently, depletion of NMD components resulted in a more than 20-fold increase in production of these attenuated viruses. These findings indicate that a cellular mRNA quality control mechanism serves as an intrinsic barrier to the translation of early viral proteins and the amplification of +RNA viruses in animal cells.
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Affiliation(s)
| | - Peter Horvath
- Synthetic and System Biology Unit, Biological Research Center, 6726 Szeged, Hungary; FIMM Institute, University of Helsinki, 00014 Helsinki, Finland
| | - Christoph Schweingruber
- Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, Switzerland; Graduate School for Cellular and Biomedical Sciences, University of Bern, 3012 Bern, Switzerland
| | - David Zünd
- Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, Switzerland
| | - Gerald McInerney
- Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, 17177 Stockholm, Sweden
| | - Andres Merits
- Institute of Technology, University of Tartu, 50090 Tartu, Estonia
| | - Oliver Mühlemann
- Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, Switzerland
| | - Claus Azzalin
- Institute of Biochemistry, ETH Zürich, 8093 Zürich, Switzerland
| | - Ari Helenius
- Institute of Biochemistry, ETH Zürich, 8093 Zürich, Switzerland
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Ahola T, Karlin DG. Sequence analysis reveals a conserved extension in the capping enzyme of the alphavirus supergroup, and a homologous domain in nodaviruses. Biol Direct 2015; 10:16. [PMID: 25886938 PMCID: PMC4392871 DOI: 10.1186/s13062-015-0050-0] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Accepted: 03/24/2015] [Indexed: 12/16/2022] Open
Abstract
Background Members of the alphavirus supergroup include human pathogens such as chikungunya virus, hepatitis E virus and rubella virus. They encode a capping enzyme with methyltransferase-guanylyltransferase (MTase-GTase) activity, which is an attractive drug target owing to its unique mechanism. However, its experimental study has proven very difficult. Results We examined over 50 genera of viruses by sequence analyses. Earlier studies showed that the MTase-GTase contains a “Core” region conserved in sequence. We show that it is followed by a long extension, which we termed “Iceberg” region, whose secondary structure, but not sequence, is strikingly conserved throughout the alphavirus supergroup. Sequence analyses strongly suggest that the minimal capping domain corresponds to the Core and Iceberg regions combined, which is supported by earlier experimental data. The Iceberg region contains all known membrane association sites that contribute to the assembly of viral replication factories. We predict that it may also contain an overlooked, widely conserved membrane-binding amphipathic helix. Unexpectedly, we detected a sequence homolog of the alphavirus MTase-GTase in taxa related to nodaviruses and to chronic bee paralysis virus. The presence of a capping enzyme in nodaviruses is biologically consistent, since they have capped genomes but replicate in the cytoplasm, where no cellular capping enzyme is present. The putative MTase-GTase domain of nodaviruses also contains membrane-binding sites that may drive the assembly of viral replication factories, revealing an unsuspected parallel with the alphavirus supergroup. Conclusions Our work will guide the functional analysis of the alphaviral MTase-GTase and the production of domains for structure determination. The identification of a homologous domain in a simple model system, nodaviruses, which replicate in numerous eukaryotic cell systems (yeast, flies, worms, mammals, and plants), can further help crack the function and structure of the enzyme. Reviewers This article was reviewed by Valerian Dolja, Eugene Koonin and Sebastian Maurer-Stroh. Electronic supplementary material The online version of this article (doi:10.1186/s13062-015-0050-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Tero Ahola
- Department of Food and Environmental Sciences, University of Helsinki, 00014, Helsinki, Finland.
| | - David G Karlin
- Department of Zoology, University of Oxford, Oxford, OX1 3PS, UK. .,The Division of Structural Biology, Henry Wellcome Building, Roosevelt Drive, Oxford, OX3 7BN, UK.
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Lehmann KC, Snijder EJ, Posthuma CC, Gorbalenya AE. What we know but do not understand about nidovirus helicases. Virus Res 2014; 202:12-32. [PMID: 25497126 PMCID: PMC7114383 DOI: 10.1016/j.virusres.2014.12.001] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2014] [Revised: 11/28/2014] [Accepted: 12/01/2014] [Indexed: 01/24/2023]
Abstract
The ubiquitous nidovirus helicase is a multi-functional enzyme of superfamily 1. Its unique N-terminal domain is most similar to the Upf1 multinuclear zinc-binding domain. It has been implicated in replication, transcription, virion biogenesis, translation and post-transcriptional viral RNA processing. Four different classes of antiviral compounds targeting the helicase have been identified.
Helicases are versatile NTP-dependent motor proteins of monophyletic origin that are found in all kingdoms of life. Their functions range from nucleic acid duplex unwinding to protein displacement and double-strand translocation. This explains their participation in virtually every metabolic process that involves nucleic acids, including DNA replication, recombination and repair, transcription, translation, as well as RNA processing. Helicases are encoded by all plant and animal viruses with a positive-sense RNA genome that is larger than 7 kb, indicating a link to genome size evolution in this virus class. Viral helicases belong to three out of the six currently recognized superfamilies, SF1, SF2, and SF3. Despite being omnipresent, highly conserved and essential, only a few viral helicases, mostly from SF2, have been studied extensively. In general, their specific roles in the viral replication cycle remain poorly understood at present. The SF1 helicase protein of viruses classified in the order Nidovirales is encoded in replicase open reading frame 1b (ORF1b), which is translated to give rise to a large polyprotein following a ribosomal frameshift from the upstream ORF1a. Proteolytic processing of the replicase polyprotein yields a dozen or so mature proteins, one of which includes a helicase. Its hallmark is the presence of an N-terminal multi-nuclear zinc-binding domain, the nidoviral genetic marker and one of the most conserved domains across members of the order. This review summarizes biochemical, structural, and genetic data, including drug development studies, obtained using helicases originating from several mammalian nidoviruses, along with the results of the genomics characterization of a much larger number of (putative) helicases of vertebrate and invertebrate nidoviruses. In the context of our knowledge of related helicases of cellular and viral origin, it discusses the implications of these results for the protein's emerging critical function(s) in nidovirus evolution, genome replication and expression, virion biogenesis, and possibly also post-transcriptional processing of viral RNAs. Using our accumulated knowledge and highlighting gaps in our data, concepts and approaches, it concludes with a perspective on future research aimed at elucidating the role of helicases in the nidovirus replication cycle.
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Affiliation(s)
- Kathleen C Lehmann
- Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Eric J Snijder
- Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Clara C Posthuma
- Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Alexander E Gorbalenya
- Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands; Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Russia.
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11
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Functional interplay among the flavivirus NS3 protease, helicase, and cofactors. Virol Sin 2014; 29:74-85. [PMID: 24691778 DOI: 10.1007/s12250-014-3438-6] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Accepted: 03/19/2014] [Indexed: 12/22/2022] Open
Abstract
Flaviviruses are positive-sense RNA viruses, and many are important human pathogens. Nonstructural protein 2B and 3 of the flaviviruses (NS2BNS3) form an endoplasmic reticulum (ER) membrane-associated hetero-dimeric complex through the NS2B transmembrane region. The NS2BNS3 complex is multifunctional. The N-terminal region of NS3, and its cofactor NS2B fold into a protease that is responsible for viral polyprotein processing, and the C-terminal domain of NS3 possesses NTPase/RNA helicase activities and is involved in viral RNA replication and virus particle formation. In addition, NS2BNS3 complex has also been shown to modulate viral pathogenesis and the host immune response. Because of the essential functions that the NS2BNS3 complex plays in the flavivirus life cycle, it is an attractive target for antiviral development. This review focuses on the recent biochemical and structural advances of NS2BNS3 and provides a brief update on the current status of drug development targeting this viral protein complex.
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12
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Tena F, Molina-Galdeano M, Serra MT, García-Luque I. A single amino acid in the helicase domain of PMMoV-S is responsible for its enhanced accumulation in C. chinense (L(3)L(3)) plants at 32°C. Virology 2012; 427:34-43. [PMID: 22377122 DOI: 10.1016/j.virol.2012.01.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2011] [Revised: 10/15/2011] [Accepted: 01/14/2012] [Indexed: 11/19/2022]
Abstract
In Capsicum chinense (L(3)L(3)) plants a higher accumulation of the tobamovirus Pepper mild mottle virus strain S (PMMoV-S) as compared to the Italian strain PMMoV-I is detected when plants are grown at 32°C. By using a reverse genetic approach, we have established that a single amino acid at position 898 in the helicase domain of the polymerase protein, outside of the conserved regions of the helicase, is critical for the higher accumulation of PMMoV-S observed. It also is necessary for both increased accumulation of viral RNA of both polarities in pepper protoplasts and enhanced cell-to-cell movement in C. chinense plants. The influence of thermoresistance of PMMoV-S, a P(1,2) pathotype, and its prevalence on pepper cultivars over PMMoV-I, a P(1,2,3), pathotype, is discussed.
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Affiliation(s)
- Fátima Tena
- Departamento de Biología Medioambiental, Centro de Investigaciones Biológicas, CSIC, C/Ramiro de Maeztu no 9, 28040 Madrid, Spain
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Pohjala L, Utt A, Varjak M, Lulla A, Merits A, Ahola T, Tammela P. Inhibitors of alphavirus entry and replication identified with a stable Chikungunya replicon cell line and virus-based assays. PLoS One 2011; 6:e28923. [PMID: 22205980 PMCID: PMC3242765 DOI: 10.1371/journal.pone.0028923] [Citation(s) in RCA: 192] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Accepted: 11/17/2011] [Indexed: 12/22/2022] Open
Abstract
Chikungunya virus (CHIKV), an alphavirus, has recently caused epidemic outbreaks and is therefore considered a re-emerging pathogen for which no effective treatment is available. In this study, a CHIKV replicon containing the virus replicase proteins together with puromycin acetyltransferase, EGFP and Renilla luciferase marker genes was constructed. The replicon was transfected into BHK cells to yield a stable cell line. A non-cytopathic phenotype was achieved by a Pro718 to Gly substitution and a five amino acid insertion within non-structural protein 2 (nsP2), obtained through selection for stable growth. Characterization of the replicon cell line by Northern blotting analysis revealed reduced levels of viral RNA synthesis. The CHIKV replicon cell line was validated for antiviral screening in 96-well format and used for a focused screen of 356 compounds (natural compounds and clinically approved drugs). The 5,7-dihydroxyflavones apigenin, chrysin, naringenin and silybin were found to suppress activities of EGFP and Rluc marker genes expressed by the CHIKV replicon. In a concomitant screen against Semliki Forest virus (SFV), their anti-alphaviral activity was confirmed and several additional inhibitors of SFV with IC₅₀ values between 0.4 and 24 µM were identified. Chlorpromazine and five other compounds with a 10H-phenothiazinyl structure were shown to inhibit SFV entry using a novel entry assay based on a temperature-sensitive SFV mutant. These compounds also reduced SFV and Sindbis virus-induced cytopathic effect and inhibited SFV virion production in virus yield experiments. Finally, antiviral effects of selected compounds were confirmed using infectious CHIKV. In summary, the presented approach for discovering alphaviral inhibitors enabled us to identify potential lead structures for the development of alphavirus entry and replication phase inhibitors as well as demonstrated the usefulness of CHIKV replicon and SFV as biosafe surrogate models for anti-CHIKV screening.
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Affiliation(s)
- Leena Pohjala
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
- Centre for Drug Research, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland
- Division of Pharmaceutical Biology, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland
| | - Age Utt
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Margus Varjak
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Aleksei Lulla
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Andres Merits
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Tero Ahola
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Päivi Tammela
- Centre for Drug Research, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland
- * E-mail:
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14
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Decroly E, Ferron F, Lescar J, Canard B. Conventional and unconventional mechanisms for capping viral mRNA. Nat Rev Microbiol 2011; 10:51-65. [PMID: 22138959 PMCID: PMC7097100 DOI: 10.1038/nrmicro2675] [Citation(s) in RCA: 328] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
mRNAs are protected at their 5′ ends by a cap structure consisting of an N7-methylated GTP molecule linked to the first transcribed nucleotide by a 5′–5′ triphosphate bond. The cap structure is essential for RNA splicing, export and stability, and allows the ribosomal complex to recognize mRNAs and ensure their efficient translation. Uncapped RNA molecules are degraded in cytoplasmic granular compartments called processing bodies and may be detected as 'non-self' by the host cell, triggering antiviral innate immune responses through the production of interferons. Conventional RNA capping (that is, of mRNAs from the host cell and from DNA viruses) requires hydrolysis of the 5′ γ-phosphate of RNA by an RNA triphosphatase, transfer of a GMP molecule onto the 5′-end of RNA by a guanylyltransferase, and methylation of this guanosine by an (guanine-N7)-methyltransferase. Subsequent methylations on the first and second transcribed nucleotides by (nucleoside-2′-O)-methyltransferases form cap-1 and cap-2 structures. Viruses have evolved highly diverse capping mechanisms to acquire cap structures using their own or cellular capping machineries, or by stealing cap structures from cellular mRNAs. Virally encoded RNA-capping machineries are diverse in terms of their genetic components, protein domain organization, enzyme structures, and reaction mechanisms and pathways, making viral RNA capping an attractive target for antiviral-drug design.
Capping the 5′ end of eukaryotic mRNAs with a 7-methylguanosine moiety enables efficient splicing, nuclear export and translation of mRNAs, and also limits their degradation by cellular exonucleases. Here, Canard and colleagues describe how viruses synthesize their own mRNA cap structures or steal them from host mRNAs, allowing efficient synthesis of viral proteins and avoidance of host innate immune responses. In the eukaryotic cell, capping of mRNA 5′ ends is an essential structural modification that allows efficient mRNA translation, directs pre-mRNA splicing and mRNA export from the nucleus, limits mRNA degradation by cellular 5′–3′ exonucleases and allows recognition of foreign RNAs (including viral transcripts) as 'non-self'. However, viruses have evolved mechanisms to protect their RNA 5′ ends with either a covalently attached peptide or a cap moiety (7-methyl-Gppp, in which p is a phosphate group) that is indistinguishable from cellular mRNA cap structures. Viral RNA caps can be stolen from cellular mRNAs or synthesized using either a host- or virus-encoded capping apparatus, and these capping assemblies exhibit a wide diversity in organization, structure and mechanism. Here, we review the strategies used by viruses of eukaryotic cells to produce functional mRNA 5′-caps and escape innate immunity.
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Affiliation(s)
- Etienne Decroly
- Centre National de Recherche Scientifique and Aix-Marseille Université, UMR 6098, Architecture et Fonction des Macromolécules Biologiques, 163 avenue de Luminy, 13288 Marseille cedex 09, France
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15
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Macromolecular assembly-driven processing of the 2/3 cleavage site in the alphavirus replicase polyprotein. J Virol 2011; 86:553-65. [PMID: 22031949 DOI: 10.1128/jvi.05195-11] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Semliki Forest virus (SFV) is a member of the Alphavirus genus, which produces its replicase proteins in the form of a nonstructural (ns) polyprotein precursor P1234. The maturation of the replicase occurs in a temporally controlled manner by protease activity of nsP2. The template preference and enzymatic capabilities of the alphaviral replication complex have a very important connection with its composition, which is irreversibly altered by proteolysis. The final cleavage of the 2/3 site in the ns polyprotein apparently leads to significant rearrangements within the replication complex and thus denotes the "point of no return" for viral replication progression. Numerous studies have devised rules for when and how ns protease acts, but how the alphaviral 2/3 site is recognized remained largely unexplained. In contrast to the other two cleavage sites within the ns polyprotein, the 2/3 site evidently lacks primary sequence elements in the vicinity of the scissile bond sufficient for specific protease recognition. In this study, we sought to investigate the molecular details of the regulation of the 2/3 site processing in the SFV ns polyprotein. We present evidence that correct macromolecular assembly, presumably strengthened by exosite interactions rather than the functionality of the individual nsP2 protease, is the driving force for specific substrate targeting. We conclude that structural elements within the macrodomain of nsP3 are used for precise positioning of a substrate recognition sequence at the catalytic center of the protease and that this process is coordinated by the exact N-terminal end of nsP2, thus representing a unique regulation mechanism used by alphaviruses.
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16
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Sakata M, Nakayama T. Protease and helicase domains are related to the temperature sensitivity of wild-type rubella viruses. Vaccine 2011; 29:1107-13. [DOI: 10.1016/j.vaccine.2010.11.074] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2010] [Revised: 11/15/2010] [Accepted: 11/21/2010] [Indexed: 10/18/2022]
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17
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Reichert E, Clase A, Bacetty A, Larsen J. Alphavirus antiviral drug development: scientific gap analysis and prospective research areas. Biosecur Bioterror 2010; 7:413-27. [PMID: 20028250 DOI: 10.1089/bsp.2009.0032] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The New World alphaviruses Venezuelan equine encephalitis virus (VEEV), eastern equine encephalitis virus (EEEV), and western equine encephalitis virus (WEEV) pose a significant threat to human health as the etiological agents of serious viral encephalitis through natural infection as well as through their potential use as a biological weapon. At present, there is no FDA-approved medical treatment for infection with these viruses. The Defense Threat Reduction Agency, Joint Science and Technology Office for Chemical and Biological Defense (DTRA/JSTO), is currently funding research aimed at developing antiviral drugs and vaccines against VEEV, EEEV, and WEEV. A review of antiviral drug discovery efforts for these viruses revealed significant gaps in the data, assays, and models required for successful drug development. This review provides a description of these gaps and highlights specific critical research areas for the development of a target-based drug discovery program for the VEEV, EEEV, and WEEV nonstructural proteins. These efforts will increase the probability of the successful development of a pharmaceutical intervention against these viral threat agents.
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Affiliation(s)
- Erin Reichert
- Biological Therapeutics, Defense Threat Reduction Agency, Fort Belvoir, Virginia 22060-6201, USA
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18
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Gould EA, Coutard B, Malet H, Morin B, Jamal S, Weaver S, Gorbalenya A, Moureau G, Baronti C, Delogu I, Forrester N, Khasnatinov M, Gritsun T, de Lamballerie X, Canard B. Understanding the alphaviruses: recent research on important emerging pathogens and progress towards their control. Antiviral Res 2009; 87:111-24. [PMID: 19616028 PMCID: PMC7114216 DOI: 10.1016/j.antiviral.2009.07.007] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2009] [Revised: 07/07/2009] [Accepted: 07/11/2009] [Indexed: 11/28/2022]
Abstract
The alphaviruses were amongst the first arboviruses to be isolated, characterized and assigned a taxonomic status. They are globally very widespread, infecting a large variety of terrestrial animals, insects and even fish, and circulate both in the sylvatic and urban/peri-urban environment, causing considerable human morbidity and mortality. Nevertheless, despite their obvious importance as pathogens, there are currently no effective antiviral drugs with which to treat humans or animals infected by any of these viruses. The EU-supported project-VIZIER (Comparative Structural Genomics of Viral Enzymes Involved in Replication, FP6 PROJECT: 2004-511960) was instigated with an ultimate view of contributing to the development of antiviral therapies for RNA viruses, including the alphaviruses [Coutard, B., Gorbalenya, A.E., Snijder, E.J., Leontovich, A.M., Poupon, A., De Lamballerie, X., Charrel, R., Gould, E.A., Gunther, S., Norder, H., Klempa, B., Bourhy, H., Rohayemj, J., L'hermite, E., Nordlund, P., Stuart, D.I., Owens, R.J., Grimes, J.M., Tuckerm, P.A., Bolognesi, M., Mattevi, A., Coll, M., Jones, T.A., Aqvist, J., Unger, T., Hilgenfeld, R., Bricogne, G., Neyts, J., La Colla, P., Puerstinger, G., Gonzalez, J.P., Leroy, E., Cambillau, C., Romette, J.L., Canard, B., 2008. The VIZIER project: preparedness against pathogenic RNA viruses. Antiviral Res. 78, 37-46]. This review highlights some of the major features of alphaviruses that have been investigated during recent years. After describing their classification, epidemiology and evolutionary history and the expanding geographic distribution of Chikungunya virus, we review progress in understanding the structure and function of alphavirus replicative enzymes achieved under the VIZIER programme and the development of new disease control strategies.
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Affiliation(s)
- E A Gould
- Institut de Recherche pour le Développement UMR190/Unité des Virus Emergents, Université de la Méditerranée, Marseille, France.
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19
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Random insertion mutagenesis of sindbis virus nonstructural protein 2 and selection of variants incapable of downregulating cellular transcription. J Virol 2009; 83:9031-44. [PMID: 19570872 DOI: 10.1128/jvi.00850-09] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Sindbis virus nonstructural protein 2 (SINV nsP2) is an important determinant of virus pathogenesis and downregulation of virus-induced cell response. This protein efficiently inhibits transcription of cellular messenger and ribosomal RNAs and, thus, is capable of inhibiting the activation of genes whose products are involved in development of the antiviral response. Alphavirus nsP2 has a number of predicted functional domains, some of which were confirmed by crystal structure. Our current study demonstrated that none of the putative or known structural domains alone or their combinations was capable of functioning in transcription inhibition. By using random, transposon-mediated mutagenesis, we generated a library of SINV nsP2 variants having short peptide insertions and selected those that lost the ability to inhibit cellular transcription and cause a cytopathic effect. Insertions abrogating the nuclear functions of the protein were found in the three different functional nsP2 domains. Some of the mutated protein variants retained the enzymatic functions required for replication of the viral genome. Such viruses were capable of efficient, productive replication in cells defective in interferon (IFN) signaling but were attenuated and incapable of spreading in cells with an intact type I IFN response. These results revealed new information about the structure of SINV nsP2 and interaction of its domains.
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20
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Fate of minus-strand templates and replication complexes produced by a p23-cleavage-defective mutant of Sindbis virus. J Virol 2009; 83:8553-64. [PMID: 19515769 DOI: 10.1128/jvi.00056-09] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
SIN2V is an engineered mutant Sindbis virus (SIN) that is unable to process the P23 cleavage site in polyproteins P123 and P1234 that are translated from the genome after its entry into cells. Unlike wild-type (wt) SIN, it caused minus strands to be made continuously and replication-transcription complex (RTC) activity to be unstable (R. Gorchakov, E. Frolova, S. Sawicki, S. Atasheva, D. Sawicki, and I. Frolov, J. Virol. 82:6218-6231, 2008). We examined further the effects of P23 on SIN RNA replication and RTC activity. Continuous minus-strand synthesis by SIN2V produced 250% of wt levels of minus strands but accumulated only 110% of wt levels (0.39 pg, or 2.7 x 10(4) molecules of double-stranded RNA per cell). Because SIN2V-infected cells accumulated only 40% of the minus strands that were made, cells must possess some process to limit RTC accumulation. The loss of activity by SIN2V RTC after translation was inhibited was stochastic and not due to their inherent instability, based on finding that activity was lost without the degradation of the minus-strand templates. In addition to their normal functions, P23 RTCs exhibited the novel phenotype of being unable to switch from making less to making more genomes than subgenomic 26S mRNA at late times during infections. Our results lend credence to the hypothesis that nsP2 (and possibly nsP3) possesses functions other than those needed solely for RTC activity and that it may also act with the host to regulate minus-strand synthesis and the stability of the RTC.
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Sakata M, Komase K, Nakayama T. Histidine at position 1042 of the p150 region of a KRT live attenuated rubella vaccine strain is responsible for the temperature sensitivity. Vaccine 2008; 27:234-42. [PMID: 18996422 DOI: 10.1016/j.vaccine.2008.10.049] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2008] [Revised: 10/02/2008] [Accepted: 10/19/2008] [Indexed: 11/27/2022]
Abstract
The Japanese live attenuated KRT rubella vaccine strain has a temperature sensitivity (ts) phenotype. The objective of this study is to identify the region responsible for this phenotype. Genomic sequences of the KRT strain and the wild-type strain (RVi/Matsue.JPN/68) with the non-ts phenotype were investigated and reverse genetic systems (RG) for these strains were developed. The ts phenotype of KRT varied drastically on replacement of the p150 gene (encoding a methyltransferase and a nonstructural protease). Analysis of four chimeric viruses showed the region responsible for the ts phenotype to be located between Bsm I and Nhe I sites (genome position 2803-3243). There were two amino acid differences at positions 1007 and 1042. Mutations were introduced into the KRT cDNA clone, designated G1007D, H1042Y and G1007D-H1042Y. H1042Y and G1007D-H1042Y grew well at a restrictive temperature with a 100-fold higher titer than G1007D and the KRT strain, but a 10-fold lower titer than RVi/Matsue.JPN/68. Since the growth of H1042Y was not completely the same as that of the wild-type strain at the restrictive temperature, we also assessed whether other genomic regions have an additive effect with H1042Y on the ts phenotype. H1042Y-RViM SP having structural proteins of RVi/Matsue.JPN/68 grew better than H1042Y, similar to RVi/Matsue.JPN/68. Thus, we concluded that one mutation, of the histidine at position 1042 of p150, was essential for the ts phenotype of the KRT strain, and structural proteins of KRT had an additive effect with H1042Y on the ts phenotype.
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Affiliation(s)
- Masafumi Sakata
- Laboratory of Viral Infection I, Kitasato Institute for Life Sciences, 5-9-1 Shirokane, Minato-ku, 108-8641 Tokyo, Japan
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22
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Molecular defects caused by temperature-sensitive mutations in Semliki Forest virus nsP1. J Virol 2008; 82:9236-44. [PMID: 18596091 DOI: 10.1128/jvi.00711-08] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Alphavirus replicase protein nsP1 has multiple functions during viral RNA synthesis. It catalyzes methyltransferase and guanylyltransferase activities needed in viral mRNA capping, attaches the viral replication complex to cytoplasmic membranes, and is required for minus-strand RNA synthesis. Two temperature-sensitive (ts) mutations in Semliki Forest virus (SFV) were previously identified within nsP1: ts10 (E529D) and ts14 (D119N). Recombinant viruses containing these individual mutations reproduced the features of the original ts strains. We now find that the capping-associated enzymatic activities of recombinant nsP1, containing ts10 or ts14 lesions, were not ts. The mutant proteins and polyproteins also were membrane bound, mutant nsP1 interacted normally with the other nonstructural proteins, and there was no major defect in nonstructural polyprotein processing in the mutants, although ts14 surprisingly displayed slightly retarded processing. The two mutant viruses were specifically defective in minus-strand RNA synthesis at the restrictive temperature. Integrating data from SFV and Sindbis virus, we discuss the domain structure of nsP1 and the relative positioning of and interactions between the replicase proteins. nsP1 is suggested to contain a specific subdomain involved in minus-strand synthesis and interaction with the polymerase nsP4 and the protease nsP2.
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23
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Role for conserved residues of sindbis virus nonstructural protein 2 methyltransferase-like domain in regulation of minus-strand synthesis and development of cytopathic infection. J Virol 2008; 82:7284-97. [PMID: 18495773 DOI: 10.1128/jvi.00224-08] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The plus-strand RNA genome of Sindbis virus (SINV) encodes four nonstructural proteins (nsP1 to nsP4) that are involved in the replication of the viral RNA. The approximately 800-amino-acid nsP2 consists of an N-terminal domain with nucleoside triphosphatase and helicase activities and a C-terminal protease domain. Recently, the structure determined for Venezuelan equine encephalitis virus nsP2 indicated the presence of a previously unrecognized methyltransferase (MTase)-like domain within the C-terminal approximately 200 residues and raised a question about its functional importance. To assess the role of this MTase-like region in viral replication, highly conserved arginine and lysine residues were mutated to alanine. The plaque phenotypes of these mutants ranged from large/wild-type to small plaques with selected mutations demonstrating temperature sensitive lethality. The proteolytic polyprotein processing activity of nsP2 was unaffected in most of the mutants. Some of the temperature-sensitive mutants showed reduction in the minus-strand RNA synthesis, a function that has not yet been ascribed to nsP2. Mutation of SINV residue R615 rendered the virus noncytopathic and incapable of inhibiting the host cell translation but with no effects on the transcriptional inhibition. This property differentiated the mutation at R615 from previously described noncytopathic mutations. These results implicate nsP2 in regulation of minus-strand synthesis and suggest that different regions of the nsP2 MTase-like domain differentially modulate host defense mechanisms, independent of its role as the viral protease.
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Casales E, Rodriguez-Madoz JR, Ruiz-Guillen M, Razquin N, Cuevas Y, Prieto J, Smerdou C. Development of a new noncytopathic Semliki Forest virus vector providing high expression levels and stability. Virology 2008; 376:242-51. [PMID: 18442838 DOI: 10.1016/j.virol.2008.03.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2008] [Revised: 03/18/2008] [Accepted: 03/18/2008] [Indexed: 10/22/2022]
Abstract
Alphavirus vectors express high levels of recombinant proteins in mammalian cells, but their cytopathic nature makes this expression transient. In order to generate a Semliki Forest virus (SFV) noncytopathic vector we introduced mutations previously described to turn Sindbis virus noncytopathic into a conserved position in an SFV vector expressing LacZ. Interestingly, mutant P718T in replicase nsp2 subunit was able to replicate in only a small percentage of BHK cells, producing beta-gal-expressing colonies without selection. Puromycin N-acetyl-transferase (pac) gene was used to replace LacZ in this mutant allowing selection of an SFV noncytopathic replicon containing a second mutation in nsp2 nuclear localization signal (R649H). This latter mutation did not confer a noncytopathic phenotype by itself and did not alter nsp2 nuclear translocation. Replicase synthesis was diminished in the SFV double mutant, leading to genomic and subgenomic RNA levels that were 125-fold and 66-fold lower than in wild-type vector, respectively. Interestingly, this mutant expressed beta-gal levels similar to parental vector. By coexpressing pac and LacZ from independent subgenomic promoters this vector was able to generate stable cell lines maintaining high expression levels during at least 10 passages, indicating that it could be used as a powerful system for protein production in mammalian cells.
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Affiliation(s)
- Erkuden Casales
- Division of Gene Therapy, School of Medicine, Center for Applied Medical Research (CIMA),University of Navarra, Av. Pio XII 55, 31008 Pamplona, Spain
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Tamm K, Merits A, Sarand I. Mutations in the nuclear localization signal of nsP2 influencing RNA synthesis, protein expression and cytotoxicity of Semliki Forest virus. J Gen Virol 2008; 89:676-686. [PMID: 18272758 PMCID: PMC2275301 DOI: 10.1099/vir.0.83320-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The cytotoxicity of Semliki Forest virus (SFV) infection is caused partly by the non-structural protein nsP2, an essential component of the SFV replicase complex. Due to the presence of a nuclear localization signal (NLS), nsP2 also localizes in the nucleus of infected cells. The present study analysed recombinant SFV replicons and genomes with various deletions or substitutions in the NLS, or with a proline-to-glycine mutation at position 718 of nsP2 (P718G). Deletion of one or two arginine residues from the NLS or substitution of two of the arginines with aspartic acid resulted in a virus with a temperature-sensitive phenotype, and substitution of all three arginines was lethal. Thus, most of the introduced mutations severely affected nsP2 functioning in viral replication; in addition, they inhibited the ability of SFV to induce translational shut-off and kill infected cells. SFV replicons with a P718G mutation or replacement of the NLS residues 648RRR650 with RDD were found to be the least cytotoxic. Corresponding replicons expressed non-structural proteins at normal levels, but had severely reduced genomic RNA synthesis and were virtually unable to replicate and transcribe co-electroporated helper RNA. The non-cytotoxic phenotype was maintained in SFV full-length genomes harbouring the corresponding mutations; however, during a single cycle of cell culture, these were converted to a cytotoxic phenotype, probably due to the accumulation of compensatory mutations.
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Affiliation(s)
- Kristi Tamm
- Estonian Biocentre, Riia 23, 51010, Tartu, Estonia
| | - Andres Merits
- Institute of Technology, University of Tartu, Nooruse 1, 50411, Tartu, Estonia.,Estonian Biocentre, Riia 23, 51010, Tartu, Estonia
| | - Inga Sarand
- Estonian Biocentre, Riia 23, 51010, Tartu, Estonia
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Han YT, Tsai CS, Chen YC, Lin MK, Hsu YH, Meng M. Mutational analysis of a helicase motif-based RNA 5'-triphosphatase/NTPase from bamboo mosaic virus. Virology 2007; 367:41-50. [PMID: 17585982 PMCID: PMC7103348 DOI: 10.1016/j.virol.2007.05.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2007] [Revised: 03/06/2007] [Accepted: 05/03/2007] [Indexed: 12/15/2022]
Abstract
The helicase-like domain of BaMV replicase possesses NTPase and RNA 5′-triphosphatase activities. In this study, mutational effects of the helicase signature motifs and residue L543 on the two activities were investigated. Either activity was inactivated by K643A-S644A, D702A, D730A, R855A, or L543P mutations. On the other hand, Q826A, D858A and L543A had activities, in terms of kcat/Km, reduced by 5- to 15-fold. AMPPNP, a nonhydrolyzable ATP analogue, competitively inhibited RNA 5′-triphosphatase activity. Analogies of mutational effects on the two activities and approximation of Ki(AMPPNP) and Km(ATP) suggest that the catalytic sites of the activities are overlapped. Mutational effects on the viral accumulation in Chenopodium quinoa indicated that the activities manifested by the domain are required for BaMV survival. Results also suggest that Q826 in motif V plays an additional role in preventing tight binding to ATP, which would otherwise decrease further RNA 5′-triphosphatase, leading to demise of the virus in plant.
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