51
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Li LH, Hsu HJ, Fischer WB. Assembling viral channel forming proteins: Vpu from HIV-1. Biopolymers 2013; 99:517-29. [DOI: 10.1002/bip.22210] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2012] [Revised: 10/17/2012] [Accepted: 12/22/2012] [Indexed: 11/09/2022]
Affiliation(s)
- Li-Hua Li
- Institute of Biophotonics, School of Biomedical Science and Engineering and Biophotonics and Molecular Imaging Research Center (BMIRC); National Yang-Ming University; Taipei 112; Taiwan
| | - Hao-Jen Hsu
- Institute of Biophotonics, School of Biomedical Science and Engineering and Biophotonics and Molecular Imaging Research Center (BMIRC); National Yang-Ming University; Taipei 112; Taiwan
| | - Wolfgang B. Fischer
- Institute of Biophotonics, School of Biomedical Science and Engineering and Biophotonics and Molecular Imaging Research Center (BMIRC); National Yang-Ming University; Taipei 112; Taiwan
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Wanka L, Iqbal K, Schreiner PR. The lipophilic bullet hits the targets: medicinal chemistry of adamantane derivatives. Chem Rev 2013; 113:3516-604. [PMID: 23432396 PMCID: PMC3650105 DOI: 10.1021/cr100264t] [Citation(s) in RCA: 441] [Impact Index Per Article: 40.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Lukas Wanka
- Institute of Organic Chemistry, Justus-Liebig University Giessen, Heinrich-Buff-Ring 58, 35392 Giessen, Germany; Fax +49(641)9934309
- Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, NY 10314-6399, USA
| | - Khalid Iqbal
- Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, NY 10314-6399, USA
| | - Peter R. Schreiner
- Institute of Organic Chemistry, Justus-Liebig University Giessen, Heinrich-Buff-Ring 58, 35392 Giessen, Germany; Fax +49(641)9934309
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Gentzsch J, Brohm C, Steinmann E, Friesland M, Menzel N, Vieyres G, Perin PM, Frentzen A, Kaderali L, Pietschmann T. hepatitis c Virus p7 is critical for capsid assembly and envelopment. PLoS Pathog 2013; 9:e1003355. [PMID: 23658526 PMCID: PMC3642076 DOI: 10.1371/journal.ppat.1003355] [Citation(s) in RCA: 92] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Accepted: 03/27/2013] [Indexed: 01/02/2023] Open
Abstract
Hepatitis C virus (HCV) p7 is a membrane-associated ion channel protein crucial for virus production. To analyze how p7 contributes to this process, we dissected HCV morphogenesis into sub-steps including recruitment of HCV core to lipid droplets (LD), virus capsid assembly, unloading of core protein from LDs and subsequent membrane envelopment of capsids. Interestingly, we observed accumulation of slowly sedimenting capsid-like structures lacking the viral envelope in cells transfected with HCV p7 mutant genomes which possess a defect in virion production. Concomitantly, core protein was enriched at the surface of LDs. This indicates a defect in core/capsid unloading from LDs and subsequent membrane envelopment rather than defective trafficking of core to this cellular organelle. Protease and ribonuclease digestion protection assays, rate zonal centrifugation and native, two dimensional gel electrophoresis revealed increased amounts of high-order, non-enveloped core protein complexes unable to protect viral RNA in cells transfected with p7 mutant genomes. These results suggest accumulation of capsid assembly intermediates that had not yet completely incorporated viral RNA in the absence of functional p7. Thus, functional p7 is necessary for the final steps of capsid assembly as well as for capsid envelopment. These results support a model where capsid assembly is linked with membrane envelopment of nascent RNA-containing core protein multimers, a process coordinated by p7. In summary, we provide novel insights into the sequence of HCV assembly events and essential functions of p7.
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Affiliation(s)
- Juliane Gentzsch
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Christiane Brohm
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Eike Steinmann
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Martina Friesland
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Nicolas Menzel
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Gabrielle Vieyres
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Paula Monteiro Perin
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Anne Frentzen
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Lars Kaderali
- Institute for Medical Informatics and Biometry, Medical Faculty, University of Technology Dresden, Dresden, Germany
| | - Thomas Pietschmann
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
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Genetic and functional characterization of the N-terminal region of the hepatitis C virus NS2 protein. J Virol 2013; 87:4130-45. [PMID: 23408609 DOI: 10.1128/jvi.03174-12] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The hepatitis C virus (HCV) NS2 protein has dual roles within the HCV life cycle. While well characterized as an autoprotease that cleaves the NS2/NS3 junction, NS2, primarily via its N-terminal region, is also involved in virion morphogenesis. In order to map the determinants necessary for infectious virus production and gain further insight into the multiple points at which NS2 may impact this process, a detailed mutational analysis of residues spanning amino acids (aa) 1 to 92 was performed. Initial block mutagenesis (5 or 7 amino acid residues) in both bicistronic and monocistronic HCV cell culture-based (HCVcc) genomes revealed that all but two blocks had various levels of impaired infectious virus production. None of these mutations affected RNA replication, indicating that the N-terminal region of NS2 is not required for NS2-3 processing and replicase assembly. Fine mapping identified 29 critical residues that, when mutated, yielded at least a 1 log decrease in infectious virus titers. These mutants were characterized further with respect to release of extracellular HCV RNA and core, intracellular infectivity, thermal stability of virus particles, and NS2 interactions. While the most severely debilitated mutants were impaired early in the assembly process, which is in agreement with previous reports, others targeted later steps of virus production, most notably egress. Thus, in addition to participating in early steps in virion assembly, this comprehensive mutagenesis study suggests yet another role for NS2 in later steps in virus production.
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Vieyres G, Brohm C, Friesland M, Gentzsch J, Wölk B, Roingeard P, Steinmann E, Pietschmann T. Subcellular localization and function of an epitope-tagged p7 viroporin in hepatitis C virus-producing cells. J Virol 2013; 87:1664-78. [PMID: 23175364 PMCID: PMC3554161 DOI: 10.1128/jvi.02782-12] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Accepted: 11/13/2012] [Indexed: 01/10/2023] Open
Abstract
The hepatitis C virus (HCV) viroporin p7 is crucial for production of infectious viral progeny. However, its role in the viral replication cycle remains incompletely understood, in part due to the poor availability of p7-specific antibodies. To circumvent this obstacle, we inserted two consecutive hemagglutinin (HA) epitope tags at its N terminus. HA-tagged p7 reduced peak virus titers ca. 10-fold and decreased kinetics of virus production compared to the wild-type virus. However, HA-tagged p7 rescued virus production of a mutant virus lacking p7, thus providing formal proof that the tag does not disrupt p7 function. In HCV-producing cells, p7 displayed a reticular staining pattern which colocalized with the HCV envelope glycoprotein 2 (E2) but also partially with viral nonstructural proteins 2, 3, and 5A. Using coimmunoprecipitation, we confirmed a specific interaction between p7 and NS2, whereas we did not detect a stable interaction with core, E2, or NS5A. Moreover, we did not observe p7 incorporation into affinity-purified virus particles. Consistently, there was no evidence supporting a role of p7 in viral entry, as an anti-HA antibody was not able to neutralize Jc1 virus produced from an HA-p7-tagged genome. Collectively, these findings highlight a stable interaction between p7 and NS2 which is likely crucial for production of infectious HCV particles. Use of this functional epitope-tagged p7 variant should facilitate the analysis of the final steps of the HCV replication cycle.
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Affiliation(s)
- Gabrielle Vieyres
- Institute of Experimental Virology, Twincore, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
| | - Christiane Brohm
- Institute of Experimental Virology, Twincore, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
| | - Martina Friesland
- Institute of Experimental Virology, Twincore, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
| | - Juliane Gentzsch
- Institute of Experimental Virology, Twincore, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
| | - Benno Wölk
- Institute of Virology, Medical School Hannover, Hannover, Germany
| | - Philippe Roingeard
- INSERM U966, Université François Rabelais, and CHRU de Tours, Tours, France
| | - Eike Steinmann
- Institute of Experimental Virology, Twincore, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
| | - Thomas Pietschmann
- Institute of Experimental Virology, Twincore, Centre for Experimental and Clinical Infection Research, a joint venture between the Medical School Hannover and the Helmholtz Centre for Infection Research, Hannover, Germany
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56
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Chandler DE, Penin F, Schulten K, Chipot C. The p7 protein of hepatitis C virus forms structurally plastic, minimalist ion channels. PLoS Comput Biol 2012; 8:e1002702. [PMID: 23028296 PMCID: PMC3447957 DOI: 10.1371/journal.pcbi.1002702] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2012] [Accepted: 07/27/2012] [Indexed: 12/20/2022] Open
Abstract
Hepatitis C virus (HCV) p7 is a membrane-associated oligomeric protein harboring ion channel activity. It is essential for effective assembly and release of infectious HCV particles and an attractive target for antiviral intervention. Yet, the self-assembly and molecular mechanism of p7 ion channelling are currently only partially understood. Using molecular dynamics simulations (aggregate time 1.2 µs), we show that p7 can form stable oligomers of four to seven subunits, with a bias towards six or seven subunits, and suggest that p7 self-assembles in a sequential manner, with tetrameric and pentameric complexes forming as intermediate states leading to the final hexameric or heptameric assembly. We describe a model of a hexameric p7 complex, which forms a transiently-open channel capable of conducting ions in simulation. We investigate the ability of the hexameric model to flexibly rearrange to adapt to the local lipid environment, and demonstrate how this model can be reconciled with low-resolution electron microscopy data. In the light of these results, a view of p7 oligomerization is proposed, wherein hexameric and heptameric complexes may coexist, forming minimalist, yet robust functional ion channels. In the absence of a high-resolution p7 structure, the models presented in this paper can prove valuable as a substitute structure in future studies of p7 function, or in the search for p7-inhibiting drugs.
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Affiliation(s)
- Danielle E. Chandler
- Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - François Penin
- Bases Moléculaires et Structurales des Systèmes Infectieux, IBCP, Université Lyon 1, Univ Lyon, France; CNRS, UMR 5086, Lyon, France
| | - Klaus Schulten
- Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Christophe Chipot
- Beckman Institute, University of Illinois at Urbana-Champaign Urbana, Illinois, United States of America
- Équipe de Dynamique des Assemblages Membranaires UMR 7565, Université de Lorraine, Vanduvre-lès-Nancy, France
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Schindler C, Fischer WB. Sequence alignment of viral channel proteins with cellular ion channels. J Comput Biol 2012; 19:1060-72. [PMID: 22891808 DOI: 10.1089/cmb.2011.0297] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Sequence alignment is an important tool for identifying regions of similarities among proteins and for, thus, establishing functional and structural relationships between different proteins. Here, alignments of transmembrane domains (TMDs) of viral channel forming proteins with host ion channels and toxins are evaluated. The following representatives of polytopic viral channel proteins are chosen: (i) p7 of HCV and 2B of Polio virus (two TMDs) and (ii) 3a of SARS-CoV (three TMDs). Using ClustalW2, each of the TMDs of the viral channels is aligned, and the overlap is mapped onto structural models of the host channels and toxins focusing on the pore-lining TMDs. The analysis reveals that p7 and 2B TMDs align with the pore-facing TMD of MscL, and 3a-TMDs align with those of ligand-gated ion channels. Possible implications concerning the mechanism of function of the viral proteins are discussed.
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Affiliation(s)
- Christina Schindler
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei, Taiwan
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58
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Abstract
Viroporins are small virally encoded hydrophobic proteins that oligomerize in the membrane of host cells, leading to the formation of hydrophilic pores. This activity modifies several cellular functions, including membrane permeability, Ca2+ homeostasis, membrane remodelling and glycoprotein trafficking. A classification scheme for viroporins is proposed on the basis of their structure and membrane topology. Thus, class I and class II viroporins are defined according to the number of transmembrane domains in the protein (one and two, respectively), and subclasses are defined according to their orientation in the membrane. The main function of viroporins during viral replication is to participate in virion morphogenesis and release from host cells. In addition, some viroporins are involved in viral entry and genome replication. The structure and activity of several viroporins, such as picornavirus protein 2B (P2B), influenza A virus matrix protein 2 (M2), hepatitis C virus p7 and HIV-1 viral protein U (Vpu), have been analysed in detail. New members of this expanding family of viral proteins have been described, from both RNA and DNA viruses. In addition to having a common general structure, all of these new viroporins have the ability to increase membrane permeability. Viroporins represent ideal targets to block viral replication and the spread of infection. Although a number of selective inhibitors of viroporin ion channels have been analysed in detail, optimized screening systems promise to provide new and more potent antiviral compounds in the near future.
Viroporins belong to a growing family of virally encoded proteins that form aqueous channels in the membranes of host cells. Here, Carrasco and colleagues review the structure and diverse biological functions of these proteins during the viral life cycle, as well as their potential as antiviral therapeutic targets. Viroporins are small, hydrophobic proteins that are encoded by a wide range of clinically relevant animal viruses. When these proteins oligomerize in host cell membranes, they form hydrophilic pores that disrupt a number of physiological properties of the cell. Viroporins are crucial for viral pathogenicity owing to their involvement in several diverse steps of the viral life cycle. Thus, these viral proteins, which include influenza A virus matrix protein 2 (M2), HIV-1 viral protein U (Vpu) and hepatitis C virus p7, represent ideal targets for therapeutic intervention, and several compounds that block their pore-forming activity have been identified. Here, we review recent studies in the field that have advanced our knowledge of the structure and function of this expanding family of viral proteins.
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Gan SW, Tan E, Lin X, Yu D, Wang J, Tan GMY, Vararattanavech A, Yeo CY, Soon CH, Soong TW, Pervushin K, Torres J. The small hydrophobic protein of the human respiratory syncytial virus forms pentameric ion channels. J Biol Chem 2012; 287:24671-89. [PMID: 22621926 DOI: 10.1074/jbc.m111.332791] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The small hydrophobic (SH) protein is encoded by the human respiratory syncytial virus. Its absence leads to viral attenuation in the context of whole organisms, and it prevents apoptosis in infected cells. Herein, we have examined the structure of SH protein in detergent micelles and in lipid bilayers, by solution NMR and attenuated total reflection-Fourier transform infrared spectroscopy, respectively. We found that SH protein has a single α-helical transmembrane domain and forms homopentamers in several detergents. In detergent micelles, the transmembrane domain is flanked N-terminally by an α-helix that forms a ring around the lumen of the pore and C-terminally by an extended β-turn. SH protein was found in the plasma membrane of transiently expressing HEK 293 cells, which showed pH-dependent (acid-activated) channel activity. Channel activity was abolished in mutants lacking both native His residues, His(22) and His(51), but not when either His was present. Herein, we propose that the pentameric model of SH protein presented is a physiologically relevant conformation, albeit probably not the only one, in which SH contributes to RSV infection and replication. Viroporins are short (∼100 amino acids) viral membrane proteins that form oligomers of a defined size, act as proton or ion channels, and in general enhance membrane permeability in the host. However, with some exceptions, their precise biological role of their channel activity is not understood. In general, viroporins resemble poorly specialized proteins but are nevertheless critical for viral fitness. In vivo, viruses lacking viroporins usually exhibit an attenuated or weakened phenotype, altered tropism, and diminished pathological effects. We have chosen to study the SH protein, 64 amino acids long, found in the human respiratory syncytial virus because of the effect of RSV on human health and the lack of adequate antivirals. We show that SH protein forms oligomers that behave as ion channels when activated at low pH. This study adds SH protein to a growing group of viroporins that have been structurally characterized. Although the precise biological role of this pentameric channel is still unknown, this report is nevertheless essential to fill some of the many gaps that exist in the understanding of SH protein function.
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Affiliation(s)
- Siok-Wan Gan
- School of Biological Sciences, Nanyang Technological University, 637551 Singapore
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Viral targets of acylguanidines. Drug Discov Today 2012; 17:1039-43. [PMID: 22580299 PMCID: PMC7108427 DOI: 10.1016/j.drudis.2012.05.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2011] [Revised: 03/12/2012] [Accepted: 05/02/2012] [Indexed: 01/01/2023]
Abstract
Acylguanidines are a new class of antiviral compounds with the unique ability to target both RNA polymerase and transmembrane proteins of viruses from different families. Importantly, they inhibit proteins which are not targeted by existing antiviral therapies, for example, Vpu of HIV type 1, p7 of hepatitis C virus, E of severe acute respiratory syndrome coronavirus and RNA-dependent RNA polymerase of coxsackievirus B3. BIT225, developed by Biotron Limited, is the first acylguanidine in clinical trials against HIV type 1 and hepatitis C virus. In this article we focus on the mechanisms of inhibition of viral proteins by acylguanidines.
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Wetherill LF, Holmes KK, Verow M, Müller M, Howell G, Harris M, Fishwick C, Stonehouse N, Foster R, Blair GE, Griffin S, Macdonald A. High-risk human papillomavirus E5 oncoprotein displays channel-forming activity sensitive to small-molecule inhibitors. J Virol 2012; 86:5341-51. [PMID: 22357280 PMCID: PMC3347351 DOI: 10.1128/jvi.06243-11] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Accepted: 02/15/2012] [Indexed: 01/12/2023] Open
Abstract
High-risk human papillomavirus type 16 (HPV16) is the primary causative agent of cervical cancer and therefore is responsible for significant morbidity and mortality worldwide. Cellular transformation is mediated directly by the expression of viral oncogenes, the least characterized of which, E5, subverts cellular proliferation and immune recognition processes. Despite a growing catalogue of E5-specific host interactions, little is understood regarding the molecular basis of its function. Here we describe a novel function for HPV16 E5 as an oligomeric channel-forming protein, placing it within the virus-encoded "viroporin" family. The development of a novel recombinant E5 expression system showed that E5 formed oligomeric assemblies of a defined luminal diameter and stoichiometry in membranous environments and that such channels mediated fluorescent dye release from liposomes. Hexameric E5 channel stoichiometry was suggested by native PAGE studies. In lieu of high-resolution structural information, established de novo molecular modeling and design methods permitted the development of the first specific small-molecule E5 inhibitor, capable of both abrogating channel activity in vitro and reducing E5-mediated effects on cell signaling pathways. The identification of channel activity should enhance the future understanding of the physiological function of E5 and could represent an important target for antiviral intervention.
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Affiliation(s)
- Laura F. Wetherill
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Kristopher K. Holmes
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Mark Verow
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Marietta Müller
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Gareth Howell
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Mark Harris
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Colin Fishwick
- School of Chemistry, University of Leeds, Leeds, United Kingdom
| | - Nicola Stonehouse
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Richard Foster
- School of Chemistry, University of Leeds, Leeds, United Kingdom
| | - G. Eric Blair
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Stephen Griffin
- Leeds Institute of Molecular Medicine, Faculty of Medicine and Health, St. James's University Hospital, University of Leeds, Leeds, United Kingdom
| | - Andrew Macdonald
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
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Li H, Atkins E, Bruckner J, McArdle S, Qiu WC, Thomassen LV, Scott J, Shuhart MC, Livingston S, Townshend-Bulson L, McMahon BJ, Harris M, Griffin S, Gretch DR. Genetic and functional heterogeneity of the hepatitis C virus p7 ion channel during natural chronic infection. Virology 2012; 423:30-7. [DOI: 10.1016/j.virol.2011.11.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Revised: 08/01/2011] [Accepted: 11/11/2011] [Indexed: 01/19/2023]
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63
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Weiser BM, Tellinghuisen TL. Structural biology of the hepatitis C virus proteins. DRUG DISCOVERY TODAY. TECHNOLOGIES 2012; 9:e175-e226. [PMID: 24064309 DOI: 10.1016/j.ddtec.2011.11.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
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64
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Fischer WB, Wang YT, Schindler C, Chen CP. Mechanism of function of viral channel proteins and implications for drug development. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2012; 294:259-321. [PMID: 22364876 PMCID: PMC7149447 DOI: 10.1016/b978-0-12-394305-7.00006-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Viral channel-forming proteins comprise a class of viral proteins which, similar to their host companions, are made to alter electrochemical or substrate gradients across lipid membranes. These proteins are active during all stages of the cellular life cycle of viruses. An increasing number of proteins are identified as channel proteins, but the precise role in the viral life cycle is yet unknown for the majority of them. This review presents an overview about these proteins with an emphasis on those with available structural information. A concept is introduced which aligns the transmembrane domains of viral channel proteins with those of host channels and toxins to give insights into the mechanism of function of the viral proteins from potential sequence identities. A summary of to date investigations on drugs targeting these proteins is given and discussed in respect of their mode of action in vivo.
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Affiliation(s)
- Wolfgang B. Fischer
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei 112, Taiwan
| | - Yi-Ting Wang
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei 112, Taiwan
| | - Christina Schindler
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei 112, Taiwan
| | - Chin-Pei Chen
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei 112, Taiwan
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65
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A concerted action of hepatitis C virus p7 and nonstructural protein 2 regulates core localization at the endoplasmic reticulum and virus assembly. PLoS Pathog 2011; 7:e1002144. [PMID: 21814513 PMCID: PMC3141040 DOI: 10.1371/journal.ppat.1002144] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2010] [Accepted: 05/15/2011] [Indexed: 02/06/2023] Open
Abstract
Hepatitis C virus (HCV) assembly remains a poorly understood process. Lipid droplets (LDs) are thought to act as platforms for the assembly of viral components. The JFH1 HCV strain replicates and assembles in association with LD-associated membranes, around which viral core protein is predominantly detected. In contrast, despite its intrinsic capacity to localize to LDs when expressed individually, we found that the core protein of the high-titer Jc1 recombinant virus was hardly detected on LDs of cell culture-grown HCV (HCVcc)-infected cells, but was mainly localized at endoplasmic reticulum (ER) membranes where it colocalized with the HCV envelope glycoproteins. Furthermore, high-titer cell culture-adapted JFH1 virus, obtained after long-term culture in Huh7.5 cells, exhibited an ER-localized core in contrast to non-adapted JFH1 virus, strengthening the hypothesis that ER localization of core is required for efficient HCV assembly. Our results further indicate that p7 and NS2 are HCV strain-specific factors that govern the recruitment of core protein from LDs to ER assembly sites. Indeed, using expression constructs and HCVcc recombinant genomes, we found that p7 is sufficient to induce core localization at the ER, independently of its ion-channel activity. Importantly, the combined expression of JFH1 or Jc1 p7 and NS2 induced the same differential core subcellular localization detected in JFH1- vs. Jc1-infected cells. Finally, results obtained by expressing p7-NS2 chimeras between either virus type indicated that compatibilities between the p7 and the first NS2 trans-membrane domains is required to induce core-ER localization and assembly of extra- and intra-cellular infectious viral particles. In conclusion, we identified p7 and NS2 as key determinants governing the subcellular localization of HCV core to LDs vs. ER and required for initiation of the early steps of virus assembly.
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Foster TL, Verow M, Wozniak AL, Bentham MJ, Thompson J, Atkins E, Weinman SA, Fishwick C, Foster R, Harris M, Griffin S. Resistance mutations define specific antiviral effects for inhibitors of the hepatitis C virus p7 ion channel. Hepatology 2011; 54:79-90. [PMID: 21520195 DOI: 10.1002/hep.24371] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
UNLABELLED The hepatitis C virus (HCV) p7 ion channel plays a critical role during infectious virus production and represents an important new therapeutic target. Its activity is blocked by structurally distinct classes of small molecules, with sensitivity varying between isolate p7 sequences. Although this is indicative of specific protein-drug interactions, a lack of high-resolution structural information has precluded the identification of inhibitor binding sites, and their modes of action remain undefined. Furthermore, a lack of clinical efficacy for existing p7 inhibitors has cast doubt over their specific antiviral effects. We identified specific resistance mutations that define the mode of action for two classes of p7 inhibitor: adamantanes and alkylated imino sugars (IS). Adamantane resistance was mediated by an L20F mutation, which has been documented in clinical trials. Molecular modeling revealed that L20 resided within a membrane-exposed binding pocket, where drug binding prevented low pH-mediated channel opening. The peripheral binding pocket was further validated by a panel of adamantane derivatives as well as a bespoke molecule designed to bind the region with high affinity. By contrast, an F25A polymorphism found in genotype 3a HCV conferred IS resistance and confirmed that these compounds intercalate between p7 protomers, preventing channel oligomerization. Neither resistance mutation significantly reduced viral fitness in culture, consistent with a low genetic barrier to resistance occurring in vivo. Furthermore, no cross-resistance was observed for the mutant phenotypes, and the two inhibitor classes showed additive effects against wild-type HCV. CONCLUSION These observations support the notion that p7 inhibitor combinations could be a useful addition to future HCV-specific therapies.
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Affiliation(s)
- Toshana L Foster
- Section of Oncology and Clinical Research, Leeds Institute of Molecular Medicine, St. James's University Hospital, Leeds, United Kingdom
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67
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Verma R, Malik C, Azmi S, Srivastava S, Ghosh S, Ghosh JK. A synthetic S6 segment derived from KvAP channel self-assembles, permeabilizes lipid vesicles, and exhibits ion channel activity in bilayer lipid membrane. J Biol Chem 2011; 286:24828-41. [PMID: 21592970 DOI: 10.1074/jbc.m110.209676] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
KvAP is a voltage-gated tetrameric K(+) channel with six transmembrane (S1-S6) segments in each monomer from the archaeon Aeropyrum pernix. The objective of the present investigation was to understand the plausible role of the S6 segment, which has been proposed to form the inner lining of the pore, in the membrane assembly and functional properties of KvAP channel. For this purpose, a 22-residue peptide, corresponding to the S6 transmembrane segment of KvAP (amino acids 218-239), and a scrambled peptide (S6-SCR) with rearrangement of only hydrophobic amino acids but without changing its composition were synthesized and characterized structurally and functionally. Although both peptides bound to the negatively charged phosphatidylcholine/phosphatidylglycerol model membrane with comparable affinity, significant differences were observed between these peptides in their localization, self-assembly, and aggregation properties onto this membrane. S6-SCR also exhibited reduced helical structures in SDS micelles and phosphatidylcholine/phosphatidylglycerol lipid vesicles as compared with the S6 peptide. Furthermore, the S6 peptide showed significant membrane-permeabilizing capability as evidenced by the release of calcein from the calcein-entrapped lipid vesicles, whereas S6-SCR showed much weaker efficacy. Interestingly, although the S6 peptide showed ion channel activity in the bilayer lipid membrane, despite having the same amino acid composition, S6-SCR was significantly inactive. The results demonstrated sequence-specific structural and functional properties of the S6 wild type peptide. The selected S6 segment is probably an important structural element that could play an important role in the membrane interaction, membrane assembly, and functional property of the KvAP channel.
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Affiliation(s)
- Richa Verma
- Molecular and Structural Biology Division, Central Drug Research Institute, Council of Scientific and Industrial Research, Chattar Manzil Palace, Lucknow 226001, India
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68
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Khaliq S, Jahan S, Hassan S. Hepatitis C virus p7: molecular function and importance in hepatitis C virus life cycle and potential antiviral target. Liver Int 2011; 31:606-17. [PMID: 21457434 DOI: 10.1111/j.1478-3231.2010.02442.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
p7, a 63-residue peptide encoded by hepatitis C virus (HCV), a major pathogen associated with a risk of developing severe liver disease, is involved in ion channel activity in lipid bilayer membranes both in in vitro and cell-based assays. p7 protein consists of two transmembrane α-helices, TM1 and TM2 connected by a loop oriented towards the cytoplasm. HCV relies on p7 function in addition to ion channel formation for efficient assembly, release and production of infectious progeny virions from liver cells. p7 activity is strictly sequence specific as mutation analysis showed the loss of ion channel function. Moreover, p7 ion channel activity can be specifically inhibited by different drugs suggesting the protein as a new target for future antiviral chemotherapy. In the present review, we focused to bring together the recent development to explore the potential role of p7 protein in HCV infection and its inhibition as a therapy.
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Affiliation(s)
- Saba Khaliq
- Functional and Applied Genomics Laboratory, National Center of Excellence in Molecular Biology, University of Punjab, Lahore, Pakistan.
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69
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Gervais C, Dô F, Cantin A, Kukolj G, White PW, Gauthier A, Vaillancourt FH. Development and validation of a high-throughput screening assay for the hepatitis C virus p7 viroporin. ACTA ACUST UNITED AC 2011; 16:363-9. [PMID: 21343600 DOI: 10.1177/1087057110396215] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The HCV p7 protein is not involved in viral RNA replication but is essential for production of infectious virus. Based on its putative ion channel activity, p7 belongs to a family of viral proteins known as viroporins that oligomerize after insertion into a lipid membrane. To screen for compounds capable of interfering with p7 channel function, a low-throughput liposome-based fluorescent dye permeability assay was modified and converted to a robust high-throughput screening assay. Escherichia coli expressing recombinant p7 were grown in high-density fed-batch fermentation followed by a detergent-free purification using a combination of affinity and reversed-phase chromatography. The phospholipid composition of the liposomes was optimized for both p7 recognition and long-term stability. A counterscreen was developed using the melittin channel-forming peptide to eliminate nonspecific screening hits. The p7 liposome-based assay displayed robust statistics (Z' > 0.75), and sensitivity to inhibition was confirmed using known inhibitors.
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Affiliation(s)
- Christian Gervais
- Department of Biological Sciences, Research and Development, Boehringer Ingelheim (Canada) Ltd., Laval, QC, Canada
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70
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Fischer WB, Hsu HJ. Viral channel forming proteins - modeling the target. BIOCHIMICA ET BIOPHYSICA ACTA 2011; 1808:561-71. [PMID: 20546700 PMCID: PMC7094444 DOI: 10.1016/j.bbamem.2010.05.014] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 05/11/2010] [Accepted: 05/14/2010] [Indexed: 01/02/2023]
Abstract
The cellular and subcellular membranes encounter an important playground for the activity of membrane proteins encoded by viruses. Viral membrane proteins, similar to their host companions, can be integral or attached to the membrane. They are involved in directing the cellular and viral reproduction, the fusion and budding processes. This review focuses especially on those integral viral membrane proteins which form channels or pores, the classification to be so, modeling by in silico methods and potential drug candidates. The sequence of an isolate of Vpu from HIV-1 is aligned with host ion channels and a toxin. The focus is on the alignment of the transmembrane domains. The results of the alignment are mapped onto the 3D structures of the respective channels and toxin. The results of the mapping support the idea of a 'channel-pore dualism' for Vpu.
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Affiliation(s)
- Wolfgang B Fischer
- Institute of Biophotonics, School of Biomedical Science and Engineering, National Yang-Ming University, Taipei, Taiwan.
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71
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Tedbury P, Welbourn S, Pause A, King B, Griffin S, Harris M. The subcellular localization of the hepatitis C virus non-structural protein NS2 is regulated by an ion channel-independent function of the p7 protein. J Gen Virol 2010; 92:819-30. [PMID: 21177929 PMCID: PMC3133701 DOI: 10.1099/vir.0.027441-0] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The hepatitis C virus (HCV) p7 ion channel and non-structural protein 2 (NS2) are both required for efficient assembly and release of nascent virions, yet precisely how these proteins are able to influence this process is unclear. Here, we provide both biochemical and cell biological evidence for a functional interaction between p7 and NS2. We demonstrate that in the context of a genotype 1b subgenomic replicon the localization of NS2 is affected by the presence of an upstream p7 with its cognate signal peptide derived from the C terminus of E2 (SPp7). Immunofluorescence analysis revealed that the presence of SPp7 resulted in the targeting of NS2 to sites closely associated with viral replication complexes. In addition, biochemical analysis demonstrated that, in the presence of SPp7, a significant proportion of NS2 was found in a detergent (Triton X-100)-insoluble fraction, which also contained a marker of detergent resistant rafts. In contrast, in replicons lacking p7, NS2 was entirely detergent soluble and the altered localization was lost. Furthermore, we found that serine 168 within NS2 was required for its localization adjacent to replication complexes, but not for its accumulation in the detergent-insoluble fraction. NS2 physically interacted with NS5A and this interaction was dependent on both p7 and serine 168 within NS2. Mutational and pharmacological analyses demonstrated that these effects were not a consequence of p7 ion channel function, suggesting that p7 possesses an alternative function that may influence the coordination of virus genome replication and particle assembly.
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Affiliation(s)
- Philip Tedbury
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
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72
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Jirasko V, Montserret R, Lee JY, Gouttenoire J, Moradpour D, Penin F, Bartenschlager R. Structural and functional studies of nonstructural protein 2 of the hepatitis C virus reveal its key role as organizer of virion assembly. PLoS Pathog 2010; 6:e1001233. [PMID: 21187906 PMCID: PMC3002993 DOI: 10.1371/journal.ppat.1001233] [Citation(s) in RCA: 150] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Accepted: 11/16/2010] [Indexed: 12/16/2022] Open
Abstract
Non-structural protein 2 (NS2) plays an important role in hepatitis C virus (HCV) assembly, but neither the exact contribution of this protein to the assembly process nor its complete structure are known. In this study we used a combination of genetic, biochemical and structural methods to decipher the role of NS2 in infectious virus particle formation. A large panel of NS2 mutations targeting the N-terminal membrane binding region was generated. They were selected based on a membrane topology model that we established by determining the NMR structures of N-terminal NS2 transmembrane segments. Mutants affected in virion assembly, but not RNA replication, were selected for pseudoreversion in cell culture. Rescue mutations restoring virus assembly to various degrees emerged in E2, p7, NS3 and NS2 itself arguing for an interaction between these proteins. To confirm this assumption we developed a fully functional JFH1 genome expressing an N-terminally tagged NS2 demonstrating efficient pull-down of NS2 with p7, E2 and NS3 and, to a lower extent, NS5A. Several of the mutations blocking virus assembly disrupted some of these interactions that were restored to various degrees by those pseudoreversions that also restored assembly. Immunofluorescence analyses revealed a time-dependent NS2 colocalization with E2 at sites close to lipid droplets (LDs) together with NS3 and NS5A. Importantly, NS2 of a mutant defective in assembly abrogates NS2 colocalization around LDs with E2 and NS3, which is restored by a pseudoreversion in p7, whereas NS5A is recruited to LDs in an NS2-independent manner. In conclusion, our results suggest that NS2 orchestrates HCV particle formation by participation in multiple protein-protein interactions required for their recruitment to assembly sites in close proximity of LDs.
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Affiliation(s)
- Vlastimil Jirasko
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany
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73
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Bartenschlager R, Penin F, Lohmann V, André P. Assembly of infectious hepatitis C virus particles. Trends Microbiol 2010; 19:95-103. [PMID: 21146993 DOI: 10.1016/j.tim.2010.11.005] [Citation(s) in RCA: 329] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Revised: 11/08/2010] [Accepted: 11/12/2010] [Indexed: 02/07/2023]
Abstract
A hallmark of the hepatitis C virus (HCV) replication cycle is its tight link with host cell lipid synthesis. This is best illustrated by the peculiar pathway used for the assembly of infectious HCV particles. Research in the past few years has shown that formation of HC-virions is closely connected to lipid droplets that could serve as an assembly platform. Moreover, HCV particle production appears to be strictly linked to very-low-density lipoproteins. In this review, we focus on new insights into the molecular aspects of the architecture and assembly of this unique type of virus particle.
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Affiliation(s)
- Ralf Bartenschlager
- Department of Infectious Diseases, Molecular Virology, Im Neuenheimer Feld 345, Heidelberg University, D-69120 Heidelberg, Germany.
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74
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Hepatitis C virus NS2 protein serves as a scaffold for virus assembly by interacting with both structural and nonstructural proteins. J Virol 2010; 85:86-97. [PMID: 20962101 DOI: 10.1128/jvi.01070-10] [Citation(s) in RCA: 121] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Many aspects of the assembly of hepatitis C virus (HCV) remain incompletely understood. To characterize the role of NS2 in the production of infectious virus, we determined NS2 interaction partners among other HCV proteins during productive infection. Pulldown assays showed that NS2 forms complexes with both structural and nonstructural proteins, including E1, E2, p7, NS3, and NS5A. Confocal microscopy also demonstrated that NS2 colocalizes with E1, E2, and NS5A in dot-like structures near lipid droplets. However, NS5A did not coprecipitate with E2 and interacted only weakly with NS3 in pulldown assays. Also, there was no demonstrable interaction between p7 and E2 or NS3 in such assays. Therefore, NS2 is uniquely capable of interacting with both structural and nonstructural proteins. Among mutations in p7, NS2, and NS3 that prevent production of infectious virus, only p7 mutations significantly reduced NS2-mediated protein interactions. These p7 mutations altered the intracellular distribution of NS2 and E2 and appeared to modulate the membrane topology of the C-terminal domain of NS2. These results suggest that NS2 acts to coordinate virus assembly by mediating interactions between envelope proteins and NS3 and NS5A within replication complexes adjacent to lipid droplets, where virus particle assembly is thought to occur. p7 may play an accessory role by regulating NS2 membrane topology, which is important for NS2-mediated protein interactions and therefore NS2 function.
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75
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Steinmann E, Pietschmann T. Hepatitis C virus p7-a viroporin crucial for virus assembly and an emerging target for antiviral therapy. Viruses 2010; 2:2078-2095. [PMID: 21994720 PMCID: PMC3185753 DOI: 10.3390/v2092078] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2010] [Revised: 09/02/2010] [Accepted: 09/06/2010] [Indexed: 12/17/2022] Open
Abstract
The hepatitis C virus (HCV), a hepatotropic plus-strand RNA virus of the family Flaviviridae, encodes a set of 10 viral proteins. These viral factors act in concert with host proteins to mediate virus entry, and to coordinate RNA replication and virus production. Recent evidence has highlighted the complexity of HCV assembly, which not only involves viral structural proteins but also relies on host factors important for lipoprotein synthesis, and a number of viral assembly co-factors. The latter include the integral membrane protein p7, which oligomerizes and forms cation-selective pores. Based on these properties, p7 was included into the family of viroporins comprising viral proteins from multiple virus families which share the ability to manipulate membrane permeability for ions and to facilitate virus production. Although the precise mechanism as to how p7 and its ion channel function contributes to virus production is still elusive, recent structural and functional studies have revealed a number of intriguing new facets that should guide future efforts to dissect the role and function of p7 in the viral replication cycle. Moreover, a number of small molecules that inhibit production of HCV particles, presumably via interference with p7 function, have been reported. These compounds should not only be instrumental in increasing our understanding of p7 function, but may, in the future, merit further clinical development to ultimately optimize HCV-specific antiviral treatments.
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Affiliation(s)
| | - Thomas Pietschmann
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +49-511-220027-130; Fax: +49-511-220027-139
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76
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Wozniak AL, Griffin S, Rowlands D, Harris M, Yi M, Lemon SM, Weinman SA. Intracellular proton conductance of the hepatitis C virus p7 protein and its contribution to infectious virus production. PLoS Pathog 2010; 6:e1001087. [PMID: 20824094 PMCID: PMC2932723 DOI: 10.1371/journal.ppat.1001087] [Citation(s) in RCA: 136] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2010] [Accepted: 08/04/2010] [Indexed: 01/27/2023] Open
Abstract
The hepatitis C virus (HCV) p7 protein is critical for virus production and an attractive antiviral target. p7 is an ion channel when reconstituted in artificial lipid bilayers, but channel function has not been demonstrated in vivo and it is unknown whether p7 channel activity plays a critical role in virus production. To evaluate the contribution of p7 to organelle pH regulation and virus production, we incorporated a fluorescent pH sensor within native, intracellular vesicles in the presence or absence of p7 expression. p7 increased proton (H(+)) conductance in vesicles and was able to rapidly equilibrate H(+) gradients. This conductance was blocked by the viroporin inhibitors amantadine, rimantadine and hexamethylene amiloride. Fluorescence microscopy using pH indicators in live cells showed that both HCV infection and expression of p7 from replicon RNAs reduced the number of highly acidic (pH<5) vesicles and increased lysosomal pH from 4.5 to 6.0. These effects were not present in uninfected cells, sub-genomic replicon cells not expressing p7, or cells electroporated with viral RNA containing a channel-inactive p7 point mutation. The acidification inhibitor, bafilomycin A1, partially restored virus production to cells electroporated with viral RNA containing the channel inactive mutation, yet did not in cells containing p7-deleted RNA. Expression of influenza M2 protein also complemented the p7 mutant, confirming a requirement for H(+) channel activity in virus production. Accordingly, exposure to acid pH rendered intracellular HCV particles non-infectious, whereas the infectivity of extracellular virions was acid stable and unaffected by incubation at low pH, further demonstrating a key requirement for p7-induced loss of acidification. We conclude that p7 functions as a H(+) permeation pathway, acting to prevent acidification in otherwise acidic intracellular compartments. This loss of acidification is required for productive HCV infection, possibly through protecting nascent virus particles during an as yet uncharacterized maturation process.
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Affiliation(s)
- Ann L. Wozniak
- Department of Internal Medicine, University of Kansas Medical Center, Kansas City, Kansas, United States of America
- Department of Neuroscience and Cell Biology, Institute for Human Infections and Immunity, University of Texas-Medical Branch, Galveston, Texas, United States of America
| | - Stephen Griffin
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences & Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
- Leeds Institute of Molecular Medicine, St James's University Hospital, University of Leeds, Leeds, United Kingdom
| | - David Rowlands
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences & Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Mark Harris
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences & Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - MinKyung Yi
- Department of Microbiology and Immunology, Institute for Human Infections and Immunity, University of Texas-Medical Branch, Galveston, Texas, United States of America
| | - Stanley M. Lemon
- Center for Infectious Diseases, University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Steven A. Weinman
- Department of Internal Medicine, University of Kansas Medical Center, Kansas City, Kansas, United States of America
- * E-mail:
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77
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A randomized controlled trial of double versus triple therapy with amantadine for genotype 1 chronic hepatitis C in Latino patients. Dig Dis Sci 2010; 55:2629-35. [PMID: 19960257 PMCID: PMC3747563 DOI: 10.1007/s10620-009-1062-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Accepted: 11/13/2009] [Indexed: 12/09/2022]
Abstract
BACKGROUND With only a third of Latinos achieving sustained virologic response (SVR), there is a need for enhanced HCV treatment. Amantadine has been proposed to improve response rates in addition to standard therapy with peginterferon alpha and ribavirin. Our objective is to evaluate whether triple therapy with amantadine improves SVR rates in this special population. METHOD Treatment-naïve Latino subjects with HCV genotype 1 infection were randomized to receive peginterferon alpha-2a plus weight-based ribavirin for 48 weeks (double therapy) or the same regimen plus amantadine 200 mg daily (triple therapy). The primary endpoint was SVR. Predictors of liver fibrosis using APRI and Forns indices were also evaluated. RESULTS We enrolled 124 patients with chronic hepatitis C genotype 1. Sixty-three received conventional therapy and 61 patients had triple therapy with amantadine. SVR at week 72 was achieved in 25 patients (39.7%) vs. 26 patients (42.6%) in the double and triple regimen, respectively (p=0.561). After multivariate analysis, advanced fibrosis, obesity, and low pretreatment ALT levels were associated with non-response in both groups (p=0.0234, p=0.0012, p=0.0249, respectively). APRI values delimited an area under the ROC curve (AUROC) of 0.724 and Forns index with AUROC of 0.733. There was no difference between both indices in predicting significant fibrosis (Knodell index: F3-F4). CONCLUSION Our study demonstrates that the addition of amantadine to standard treatment of chronic HCV does not improve SVR rates in Latino patients with genotype 1. Further research to improve response rates in this special population is needed.
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78
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Tews BA, Popescu CI, Dubuisson J. Last stop before exit - hepatitis C assembly and release as antiviral drug targets. Viruses 2010; 2:1782-1803. [PMID: 21994707 PMCID: PMC3185729 DOI: 10.3390/v2081782] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 07/16/2010] [Accepted: 08/04/2010] [Indexed: 12/15/2022] Open
Abstract
Chronic Hepatitis C infection is a global health problem. While primary infection is often inapparent, it becomes chronic in most cases. Chronic infection with Hepatitis C virus (HCV) frequently leads to liver cirrhosis or liver cancer. Consequently, HCV infection is one of the leading causes for liver transplantation in industrialized countries. Current treatment is not HCV specific and is only effective in about half of the infected patients. This situation underlines the need for new antivirals against HCV. To develop new and more efficient drugs, it is essential to specifically target the different steps of the viral life cycle. Of those steps, the targeting of HCV assembly has the potential to abolish virus production. This review summarizes the advances in our understanding of HCV particle assembly and the identification of new antiviral targets of potential interest in this late step of the HCV life cycle.
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Affiliation(s)
- Birke Andrea Tews
- Hepatitis C Laboratory, Center of Infection and Immunity of Lille, University Lille Nord de France, CNRS UMR8204, INSERM U1019, Pasteur Institute of Lille, 1, rue du professeur Calmette, BP447, 59021 Lille, France; E-Mails: (C.-I.P.); (J.D.)
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +33-320-87-1162; Fax: +33-320-87-1201
| | - Costin-Ioan Popescu
- Hepatitis C Laboratory, Center of Infection and Immunity of Lille, University Lille Nord de France, CNRS UMR8204, INSERM U1019, Pasteur Institute of Lille, 1, rue du professeur Calmette, BP447, 59021 Lille, France; E-Mails: (C.-I.P.); (J.D.)
- Institute of Biochemistry of the Romanian Academy, Splaiul Independentei 296, 060031, Bucharest, Romania
| | - Jean Dubuisson
- Hepatitis C Laboratory, Center of Infection and Immunity of Lille, University Lille Nord de France, CNRS UMR8204, INSERM U1019, Pasteur Institute of Lille, 1, rue du professeur Calmette, BP447, 59021 Lille, France; E-Mails: (C.-I.P.); (J.D.)
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79
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Liang X, Li ZY. Ion channels as antivirus targets. Virol Sin 2010; 25:267-80. [PMID: 20960300 DOI: 10.1007/s12250-010-3136-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Accepted: 05/10/2010] [Indexed: 10/19/2022] Open
Abstract
Ion channels are membrane proteins that are found in a number of viruses and which are of crucial physiological importance in the viral life cycle. They have one common feature in that their action mode involves a change of electrochemical or proton gradient across the bilayer lipid membrane which modulates viral or cellular activity. We will discuss a group of viral channel proteins that belong to the viroproin family, and which participate in a number of viral functions including promoting the release of viral particles from cells. Blocking these channel-forming proteins may be "lethal", which can be a suitable and potential therapeutic strategy. In this review we discuss seven ion channels of viruses which can lead serious infections in human beings: M2 of influenza A, NB and BM2 of influenza B, CM2 of influenza C, Vpu of HIV-1, p7 of HCV and 2B of picornaviruses.
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Affiliation(s)
- Xin Liang
- State Key Laboratory of Respiratory Diseases, Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, 510530, China
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80
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Montserret R, Saint N, Vanbelle C, Salvay AG, Simorre JP, Ebel C, Sapay N, Renisio JG, Böckmann A, Steinmann E, Pietschmann T, Dubuisson J, Chipot C, Penin F. NMR structure and ion channel activity of the p7 protein from hepatitis C virus. J Biol Chem 2010; 285:31446-61. [PMID: 20667830 DOI: 10.1074/jbc.m110.122895] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The small membrane protein p7 of hepatitis C virus forms oligomers and exhibits ion channel activity essential for virus infectivity. These viroporin features render p7 an attractive target for antiviral drug development. In this study, p7 from strain HCV-J (genotype 1b) was chemically synthesized and purified for ion channel activity measurements and structure analyses. p7 forms cation-selective ion channels in planar lipid bilayers and at the single-channel level by the patch clamp technique. Ion channel activity was shown to be inhibited by hexamethylene amiloride but not by amantadine. Circular dichroism analyses revealed that the structure of p7 is mainly α-helical, irrespective of the membrane mimetic medium (e.g. lysolipids, detergents, or organic solvent/water mixtures). The secondary structure elements of the monomeric form of p7 were determined by (1)H and (13)C NMR in trifluoroethanol/water mixtures. Molecular dynamics simulations in a model membrane were combined synergistically with structural data obtained from NMR experiments. This approach allowed us to determine the secondary structure elements of p7, which significantly differ from predictions, and to propose a three-dimensional model of the monomeric form of p7 associated with the phospholipid bilayer. These studies revealed the presence of a turn connecting an unexpected N-terminal α-helix to the first transmembrane helix, TM1, and a long cytosolic loop bearing the dibasic motif and connecting TM1 to TM2. These results provide the first detailed experimental structural framework for a better understanding of p7 processing, oligomerization, and ion channel gating mechanism.
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Affiliation(s)
- Roland Montserret
- Institut de Biologie et Chimie des Protéines, UMR 5086, CNRS, Université de Lyon, IFR128 BioSciences Gerland-Lyon Sud, 69367 Lyon, France
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81
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Lange CM, Sarrazin C, Zeuzem S. Review article: specifically targeted anti-viral therapy for hepatitis C - a new era in therapy. Aliment Pharmacol Ther 2010; 32:14-28. [PMID: 20374226 DOI: 10.1111/j.1365-2036.2010.04317.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
BACKGROUND Novel, directly acting anti-viral agents, also named 'specifically targeted anti-viral therapy for hepatitis C' (STAT-C) compounds, are currently under development. AIM To review the potential of STAT-C agents which are currently under clinical development, with a focus on agents that target HCV proteins. METHODS Studies evaluating STAT-C compounds were identified by systematic literature search using PubMed as well as databases of abstracts presented in English at recent liver and gastroenterology congresses. RESULTS Numerous directly-acting anti-viral agents are currently under clinical phase I-III evaluation. Final results of phase II clinical trials evaluating the most advanced compounds telaprevir and boceprevir indicate that the addition of these NS3/4A protease inhibitors to pegylated interferon-alfa and ribavirin strongly improves the chance to achieve a SVR in treatment-naive HCV genotype 1 patient as well as in prior nonresponders and relapsers to standard therapy. Monotherapy with directly acting anti-virals is not suitable. NS5B polymerase inhibitors in general have a lower anti-viral efficacy than protease inhibitors. CONCLUSIONS STAT-C compounds in addition to pegylated interferon-alfa and ribavirin can improve SVR rates at least in HCV genotype 1 patients. Future research needs to evaluate whether a SVR can be achieved by combination therapies of STAT-C compounds in interferon-free regimens.
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Affiliation(s)
- C M Lange
- Department of Medicine, Johann Wolfgang Goethe University, Frankfurt am Main, Germany
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82
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Carter SD, Dent KC, Atkins E, Foster TL, Verow M, Gorny P, Harris M, Hiscox JA, Ranson NA, Griffin S, Barr JN. Direct visualization of the small hydrophobic protein of human respiratory syncytial virus reveals the structural basis for membrane permeability. FEBS Lett 2010; 584:2786-90. [PMID: 20471980 PMCID: PMC2896471 DOI: 10.1016/j.febslet.2010.05.006] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2010] [Revised: 04/29/2010] [Accepted: 05/03/2010] [Indexed: 12/02/2022]
Abstract
Human respiratory syncytial virus (HRSV) is the leading cause of lower respiratory tract disease in infants. The HRSV small hydrophobic (SH) protein plays an important role in HRSV pathogenesis, although its mode of action is unclear. Analysis of the ability of SH protein to induce membrane permeability and form homo-oligomers suggests it acts as a viroporin. For the first time, we directly observed functional SH protein using electron microscopy, which revealed SH forms multimeric ring-like objects with a prominent central stained region. Based on current and existing functional data, we propose this region represents the channel that mediates membrane permeability. Structured summary MINT-7890792, MINT-7890805: SH (uniprotkb:P04852) and SH (uniprotkb:P04852) bind (MI:0407) by chromatography technology (MI:0091) MINT-7890784, MINT-7890776: SH (uniprotkb:P04852) and SH (uniprotkb:P04852) bind (MI:0407) by electron microscopy (MI:0040)
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Affiliation(s)
- Stephen D Carter
- Institute for Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK
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83
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Luscombe CA, Huang Z, Murray MG, Miller M, Wilkinson J, Ewart GD. A novel Hepatitis C virus p7 ion channel inhibitor, BIT225, inhibits bovine viral diarrhea virus in vitro and shows synergism with recombinant interferon-alpha-2b and nucleoside analogues. Antiviral Res 2010; 86:144-53. [PMID: 20156486 DOI: 10.1016/j.antiviral.2010.02.312] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2009] [Revised: 12/21/2009] [Accepted: 02/04/2010] [Indexed: 11/16/2022]
Abstract
The novel small molecule, BIT225 (N-[5-(1-methyl-1H-pyrazol-4-yl)-napthalene-2-carbonyl]-guanidine: CAS No. 917909-71-8), was initially identified using a screening strategy designed to detect inhibitors of Hepatitis C virus (HCV) p7 ion channel activity. Here we report that BIT225 has potent stand-alone antiviral activity against the HCV model pestivirus bovine viral diarrhea virus (BVDV) with an IC(50) of 314nM. Combinations of BIT225 with recombinant interferon alpha-2b (rIFNalpha-2b) show synergistic antiviral action against BVDV and the synergy is further enhanced by addition of ribavirin. Synergy was also observed between BIT225 and two nucleoside analogues known to inhibit the HCV RNA-dependent RNA polymerase. BIT225 has successfully completed a phase Ia dose escalating, single dose safety trial in healthy volunteers and a phase Ib/IIa trial to evaluate the safety and pharmacokinetics of repeated dosing for selected doses of BIT225 in HCV-infected persons. A modest, but statistically significant drop in patient viral load was detected over the 7 days of dosing (ref. www.biotron.com.au). Given the critical role of the p7 protein in the HCV life cycle and pathogenicity, our data indicate that molecules like BIT225, representing a new class of antiviral compounds, may be developable for therapeutic use against HCV infection, either as monotherapy, or in combination with other HCV drugs.
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84
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Characterization of determinants important for hepatitis C virus p7 function in morphogenesis by using trans-complementation. J Virol 2009; 83:11682-93. [PMID: 19726506 DOI: 10.1128/jvi.00691-09] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Hepatitis C virus (HCV) p7 is an integral membrane protein that forms ion channels in vitro and that is crucial for the efficient assembly and release of infectious virions. Due to these properties, p7 was included in the family of viroporins that comprises proteins like influenza A virus M2 and human immunodeficiency virus type 1 (HIV-1) vpu, which alter membrane permeability and facilitate the release of infectious viruses. p7 from different HCV isolates sustains virus production with variable efficiency. Moreover, p7 determinants modulate processing at the E2/p7 and the p7/NS2 signal peptidase cleavage sites, and E2/p7 cleavage is incomplete. Consequently, it was unclear if a differential ability to sustain virus production was due to variable ion channel activity or due to alternate processing at these sites. Therefore, we developed a trans-complementation assay permitting the analysis of p7 outside of the HCV polyprotein and thus independently of processing. The rescue of p7-defective HCV genomes was accomplished by providing E2, p7, and NS2, or, in some cases, by p7 alone both in a transient complementation assay as well as in stable cell lines. In contrast, neither influenza A virus M2 nor HIV-1 vpu compensated for defective p7 in HCV morphogenesis. Thus, p7 is absolutely essential for the production of infectious HCV particles. Moreover, our data indicate that p7 can operate independently of an upstream signal sequence, and that a tyrosine residue close to the conserved dibasic motif of p7 is important for optimal virus production in the context of genotype 2a viruses. The experimental system described here should be helpful to investigate further key determinants of p7 that are essential for its structure and function in the absence of secondary effects caused by altered polyprotein processing.
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85
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The 3-dimensional structure of a hepatitis C virus p7 ion channel by electron microscopy. Proc Natl Acad Sci U S A 2009; 106:12712-6. [PMID: 19590017 PMCID: PMC2722341 DOI: 10.1073/pnas.0905966106] [Citation(s) in RCA: 128] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Infection with the hepatitis C virus (HCV) has a huge impact on global health putting more than 170 million people at risk of developing severe liver disease. The HCV encoded p7 ion channel is essential for the production of infectious viruses. Despite a growing body of functional data, little is known about the 3-dimensional (3D) structure of the channel. Here, we present the 3D structure of a full-length viroporin, the detergent-solubilized hexameric 42 kDa form of the HCV p7 ion channel, as determined by single-particle electron microscopy using the random conical tilting approach. The reconstruction of such a small protein complex was made possible by a combination of high-contrast staining, the symmetry, and the distinct structural features of the channel. The orientation of the p7 monomers within the density was established using immunolabeling with N and C termini specific F(ab) fragments. The density map at a resolution of approximately 16 A reveals a flower-shaped protein architecture with protruding petals oriented toward the ER lumen. This broadest part of the channel presents a comparatively large surface area providing potential interaction sites for cellular and virally encoded ER resident proteins.
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86
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Meier V, Ramadori G. Hepatitis C virus virology and new treatment targets. Expert Rev Anti Infect Ther 2009; 7:329-50. [PMID: 19344246 DOI: 10.1586/eri.09.12] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Hepatitis C virus (HCV) infection is the leading cause of chronic liver disease. An estimated 130 million people worldwide are persistently infected with HCV. Almost half of patients who have chronic HCV infection cannot be cured with the standard treatment consisting of pegylated IFN-alpha and ribavirin. For those patients who do not respond to this standard antiviral therapy, there is currently no approved treatment option available. Recent progress in structure determination of HCV proteins and development of a subgenomic replicon system enables the development of a specifically targeted antiviral therapy for hepatitis C. Many HCV-specific compounds are now under investigation in preclinical and clinical trials.
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Affiliation(s)
- Volker Meier
- Universitätsmedizin Göttingen, Abteilung für Gastroenterologie und Endokrinologie, Göttingen, Germany
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87
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Determinants of hepatitis C virus p7 ion channel function and drug sensitivity identified in vitro. J Virol 2009; 83:7970-81. [PMID: 19493992 DOI: 10.1128/jvi.00521-09] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Hepatitis C virus (HCV) chronically infects 170 million individuals, causing severe liver disease. Although antiviral chemotherapy exists, the current regimen is ineffective in 50% of cases due to high levels of innate virus resistance. New, virus-specific therapies are forthcoming although their development has been slow and they are few in number, driving the search for new drug targets. The HCV p7 protein forms an ion channel in vitro and is critical for the secretion of infectious virus. p7 displays sensitivity to several classes of compounds, making it an attractive drug target. We recently demonstrated that p7 compound sensitivity varies according to viral genotype, yet little is known of the residues within p7 responsible for channel activity or drug interactions. Here, we have employed a liposome-based assay for p7 channel function to investigate the genetic basis for compound sensitivity. We demonstrate using chimeric p7 proteins that neither the two trans-membrane helices nor the p7 basic loop individually determines compound sensitivity. Using point mutation analysis, we identify amino acids important for channel function and demonstrate that null mutants exert a dominant negative effect over wild-type protein. We show that, of the three hydrophilic regions within the amino-terminal trans-membrane helix, only the conserved histidine at position 17 is important for genotype 1b p7 channel activity. Mutations predicted to play a structural role affect both channel function and oligomerization kinetics. Lastly, we identify a region at the p7 carboxy terminus which may act as a specific sensitivity determinant for the drug amantadine.
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88
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Murray CL, Jones CT, Rice CM. Architects of assembly: roles of Flaviviridae non-structural proteins in virion morphogenesis. Nat Rev Microbiol 2009; 6:699-708. [PMID: 18587411 DOI: 10.1038/nrmicro1928] [Citation(s) in RCA: 177] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Viruses of the Flaviviridae family, including hepatitis C, dengue and bovine viral diarrhoea, are responsible for considerable morbidity and mortality worldwide. Recent advances in our understanding of virion assembly have uncovered commonalities among distantly related members of this family. We discuss the emerging hypothesis that physical virion components are not alone in forming the infectious particle, but that non-structural proteins are intimately involved in orchestrating morphogenesis. Pinpointing the roles of Flaviviridae proteins in virion production could reveal new avenues for antiviral therapeutics.
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89
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Abstract
The p7 membrane polypeptide from HCV is essential for virus infection. It exhibits ion-channel activity reported to be specifically blocked by various compounds. These properties make p7 an attractive candidate target for antiviral intervention to combat viral hepatitis C infection. In this context, in vitro functional analyses of isolated p7 coupled to structural characterization are critical for further understanding of the molecular mechanisms of p7 ion-channel activity and for the development of new antiviral drugs. We present here in vitro assays designed to purify synthetic p7 by RP-HPLC, to investigate its ion-channel properties by means of planar lipid-bilayer assays and patch-clamp recordings after reconstitution into liposomes, and to analyze its structural features by circular dichroism (CD), nuclear magnetic resonance (NMR), and molecular dynamics (MD).
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90
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Meshkat Z, Audsley M, Beyer C, Gowans EJ, Haqshenas G. Reverse genetic analysis of a putative, influenza virus M2 HXXXW-like motif in the p7 protein of hepatitis C virus. J Viral Hepat 2009; 16:187-94. [PMID: 19175872 DOI: 10.1111/j.1365-2893.2008.01064.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The p7 protein of hepatitis C virus (HCV) has been classified into a family of viral proteins, designated viroporins that form ion channels. The M2 protein of influenza virus is the prototype viroporin and encodes a HXXXW motif that constitutes the main functional element of the M2 channels. Alignment of different p7 proteins revealed that a HXXXW sequence (positions 17-21) is also highly conserved among some HCV genotypes. To study the putative HXXXW motif in p7, five mutants of the Japanese fulminant hepatitis 1 strain of HCV that encoded H17A, H17G, H17E, Y21A and Y21W were generated. After transfection of human hepatoma cells with the mutant transcripts, unlike H17A and H17G that produced up to 1 log lower viral titres than wild type, H17E and Y21W showed slightly higher infectivity. In conclusion, this study demonstrated that the HXXXW sequence exists in the p7 proteins of some HCV genotypes and that H17 plays an important role in virus replication.
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Affiliation(s)
- Z Meshkat
- The Macfarlane Burnet Institute, Melbourne, Vic, Australia
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91
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Chew CF, Vijayan R, Chang J, Zitzmann N, Biggin PC. Determination of pore-lining residues in the hepatitis C virus p7 protein. Biophys J 2009; 96:L10-2. [PMID: 19167280 DOI: 10.1016/j.bpj.2008.10.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2008] [Accepted: 10/16/2008] [Indexed: 01/16/2023] Open
Abstract
The p7 protein from hepatitis C virus is critical for the assembly and secretion of infectious virus, making it an attractive drug target. It is thought to be a viroporin with a demonstrated ion channel activity when reconstituted into planar lipid bilayers. Electron microscopy experiments suggest that p7 oligomers coexist as hexamers and heptamers. Proposed models of p7 oligomers assume the N-terminal helix to be the pore lining helix. Here, we demonstrate, via electrophysiology, that Cu(2+) has an inhibitory effect on the p7 ion channel and that the amino acid responsible for this inhibition is one histidine in each monomer. This information coupled with the p7 sequence data suggests that the N-terminal helix of p7 does indeed form the transmembrane pore and that this histidine is pore-lining. The information will aid in the construction of oligomeric pore-models and the interpretation of electron microscopy data.
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92
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Andreeva-Kovalevskaya ZI, Solonin AS, Sineva EV, Ternovsky VI. Pore-forming proteins and adaptation of living organisms to environmental conditions. BIOCHEMISTRY (MOSCOW) 2009; 73:1473-92. [DOI: 10.1134/s0006297908130087] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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93
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Abstract
Channel-forming proteins are found in a number of viral genomes. In some cases, their role in the viral life cycle is well understood, in some cases it needs still to be elucidated. A common theme is that their mode of action involves a change of electrochemical or proton gradient across the lipid membrane which modulates the viral or cellular activity. Blocking these proteins can be a suitable therapeutic strategy as for some viruses this may be "lethal." Besides the many biological relevant questions still to be answered, there are also many open questions concerning the biophysical side as well as structural information and the mechanism of function on a molecular level. The immanent biophysical issues are addressed and the work in the field is summarized.
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94
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Griffin S, StGelais C, Owsianka AM, Patel AH, Rowlands D, Harris M. Genotype-dependent sensitivity of hepatitis C virus to inhibitors of the p7 ion channel. Hepatology 2008; 48:1779-90. [PMID: 18828153 PMCID: PMC7615706 DOI: 10.1002/hep.22555] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
UNLABELLED The hepatitis C virus (HCV) p7 protein plays a critical role during particle formation in cell culture and is required for virus replication in chimpanzees. The discovery that it displayed cation channel activity in vitro led to its classification within the "viroporin" family of virus-coded ion channel proteins, which includes the influenza A virus (IAV) M2 protein. Like M2, p7 was proposed as a potential target for much needed new HCV therapies, and this was supported by our finding that the M2 inhibitor, amantadine, blocked its activity in vitro. Since then, further compounds have been shown to inhibit p7 function but the relationship between inhibitory effects in vitro and efficacy against infectious virus is controversial. Here, we have sought to validate multiple p7 inhibitor compounds using a parallel approach combining the HCV infectious culture system and a rapid throughput in vitro assay for p7 function. We identify a genotype-dependent and subtype-dependent sensitivity of HCV to p7 inhibitors, in which results in cell culture largely mirror the sensitivity of recombinant protein in vitro; thus building separate sensitivity profiles for different p7 sequences. Inhibition of virus entry also occurred, suggesting that p7 may be a virion component. Second site effects on both cellular and viral processes were identified for several compounds in addition to their efficacy against p7 in vitro. Nevertheless, for some compounds antiviral effects were specific to a block of ion channel function. CONCLUSION These data validate p7 inhibitors as prototype therapies for chronic HCV disease. (HEPATOLOGY 2008;48:1779-1790.).
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Affiliation(s)
- Stephen Griffin
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Corine StGelais
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Ania M. Owsianka
- Medical Research Council Virology Unit, Church Street, Glasgow, UK
| | - Arvind H. Patel
- Medical Research Council Virology Unit, Church Street, Glasgow, UK
| | - David Rowlands
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Mark Harris
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
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95
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Griffin S, Trowbridge R, Thommes P, Parry N, Rowlands D, Harris M, Bright H. Chimeric GB virus B genomes containing hepatitis C virus p7 are infectious in vivo. J Hepatol 2008; 49:908-15. [PMID: 18845353 PMCID: PMC3098382 DOI: 10.1016/j.jhep.2008.07.020] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 06/20/2008] [Accepted: 07/07/2008] [Indexed: 01/02/2023]
Abstract
BACKGROUND/AIMS The development of new therapies for hepatitis C virus (HCV) infection has been hampered by the lack of a small animal model. GB virus B (GBV-B), which infects new world monkeys, has been proposed as a surrogate system for HCV replication. Despite their short genetic distance, however, difficulties exist when extrapolating results from GBV-B to the HCV system. One way of addressing this is the creation of chimeric GBV-B containing HCV elements. METHODS Construction and analysis of GBV-B chimeras in which the p13 ion channel was replaced by its HCV counterpart, p7. RESULTS Replacing all, or part of, the GBV-B p13 protein with HCV p7 resulted in viable chimeras which replicated at wild-type levels in marmosets following intra-hepatic RNA injection. Serum from one animal injected with chimeric RNA was infectious in three naïve recipients, indicating that chimeras formed fully infectious virions. Amantadine, which blocks the ion channel activity of both HCV and GBV-B proteins in vitro, also inhibited GBV-B replication in primary hepatocytes. CONCLUSIONS These viruses highlight the potential for chimeric GBV-B in the development of HCV-specific therapies and will provide a means of developing HCV p7 as a therapeutic target.
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Affiliation(s)
- Stephen Griffin
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.
| | - Rachel Trowbridge
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Pia Thommes
- Department of Virology, GSK Medicines Research Centre, Stevenage, UK
| | - Nigel Parry
- Department of Virology, GSK Medicines Research Centre, Stevenage, UK
| | - David Rowlands
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Mark Harris
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Helen Bright
- Department of Virology, GSK Medicines Research Centre, Stevenage, UK
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96
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Gottwein JM, Bukh J. Cutting the gordian knot-development and biological relevance of hepatitis C virus cell culture systems. Adv Virus Res 2008; 71:51-133. [PMID: 18585527 DOI: 10.1016/s0065-3527(08)00002-x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Worldwide approximately 180 million people are chronically infected with hepatitis C virus (HCV). HCV isolates exhibit extensive genetic heterogeneity and have been grouped in six genotypes and various subtypes. Additionally, several naturally occurring intergenotypic recombinants have been described. Research on the viral life cycle, efficient therapeutics, and a vaccine has been hampered by the absence of suitable cell culture systems. The first system permitting studies of the full viral life cycle was intrahepatic transfection of RNA transcripts of HCV consensus complementary DNA (cDNA) clones into chimpanzees. However, such full-length clones were not infectious in vitro. The development of the replicon system and HCV pseudo-particles allowed in vitro studies of certain aspects of the viral life cycle, RNA replication, and viral entry, respectively. Identification of the genotype 2 isolate JFH1, which for unknown reasons showed an exceptional replication capability and resulted in formation of infectious viral particles in the human hepatoma cell line Huh7, led in 2005 to the development of the first full viral life cycle in vitro systems. JFH1-based systems now enable in vitro studies of the function of viral proteins, their interaction with each other and host proteins, new antivirals, and neutralizing antibodies in the context of the full viral life cycle. However, several challenges remain, including development of cell culture systems for all major HCV genotypes and identification of other susceptible cell lines.
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Affiliation(s)
- Judith M Gottwein
- Copenhagen Hepatitis C Program (CO-HEP), Department of Infectious Diseases and Clinical Research Centre, Copenhagen University Hospital, Hvidovre, Denmark
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97
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Kronenberger B, Welsch C, Forestier N, Zeuzem S. Novel hepatitis C drugs in current trials. Clin Liver Dis 2008; 12:529-55, viii. [PMID: 18625427 DOI: 10.1016/j.cld.2008.03.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Almost half of the patients who have chronic hepatitis C cannot be cured with the current standard treatment. Recent progress in structure determination of HCV proteins and development of a subgenomic replicon system and a cell culture infectious HCV clone enabled the development of a specifically targeted antiviral therapy for hepatitis C (STAT-C). Many HCV-specific compounds are under investigation in preclinical and clinical trials. The development of agents in different classes may allow construction of antiviral combinations that enhance the effectiveness of antiviral treatment, reduce the duration of treatment, and, eventually, may even avoid the use of interferon-alfa.
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Affiliation(s)
- Bernd Kronenberger
- Zentrum der Inneren Medizin, Medizinische Klinik 1, Klinikum der Johann Wolfgang Goethe-Universität, Frankfurt, Germany
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98
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Hepatitis C virus p7 protein is crucial for assembly and release of infectious virions. PLoS Pathog 2008. [PMID: 17658949 DOI: 10.1371/journal.ppat.0030103.] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Hepatitis C virus (HCV) infection is associated with chronic liver disease and currently affects about 3% of the world population. Although much has been learned about the function of individual viral proteins, the role of the HCV p7 protein in virus replication is not known. Recent data, however, suggest that it forms ion channels that may be targeted by antiviral compounds. Moreover, this protein was shown to be essential for infectivity in chimpanzee. Employing the novel HCV infection system and using a genetic approach to investigate the function of p7 in the viral replication cycle, we find that this protein is essential for efficient assembly and release of infectious virions across divergent virus strains. We show that p7 promotes virus particle production in a genotype-specific manner most likely due to interactions with other viral factors. Virus entry, on the other hand, is largely independent of p7, as the specific infectivity of released virions with a defect in p7 was not affected. Together, these observations indicate that p7 is primarily involved in the late phase of the HCV replication cycle. Finally, we note that p7 variants from different isolates deviate substantially in their capacity to promote virus production, suggesting that p7 is an important virulence factor that may modulate fitness and in turn virus persistence and pathogenesis.
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99
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Steinmann E, Penin F, Kallis S, Patel AH, Bartenschlager R, Pietschmann T. Hepatitis C virus p7 protein is crucial for assembly and release of infectious virions. PLoS Pathog 2008; 3:e103. [PMID: 17658949 PMCID: PMC1924870 DOI: 10.1371/journal.ppat.0030103] [Citation(s) in RCA: 268] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2007] [Accepted: 06/07/2007] [Indexed: 12/11/2022] Open
Abstract
Hepatitis C virus (HCV) infection is associated with chronic liver disease and currently affects about 3% of the world population. Although much has been learned about the function of individual viral proteins, the role of the HCV p7 protein in virus replication is not known. Recent data, however, suggest that it forms ion channels that may be targeted by antiviral compounds. Moreover, this protein was shown to be essential for infectivity in chimpanzee. Employing the novel HCV infection system and using a genetic approach to investigate the function of p7 in the viral replication cycle, we find that this protein is essential for efficient assembly and release of infectious virions across divergent virus strains. We show that p7 promotes virus particle production in a genotype-specific manner most likely due to interactions with other viral factors. Virus entry, on the other hand, is largely independent of p7, as the specific infectivity of released virions with a defect in p7 was not affected. Together, these observations indicate that p7 is primarily involved in the late phase of the HCV replication cycle. Finally, we note that p7 variants from different isolates deviate substantially in their capacity to promote virus production, suggesting that p7 is an important virulence factor that may modulate fitness and in turn virus persistence and pathogenesis. The hepatitis C virus (HCV), a major human pathogen associated with severe liver disease, encodes a small membrane protein designated p7. Although recent reports indicated that p7 forms channels conducting ions across membranes and is essential for HCV infection, its exact role in the viral life cycle remained elusive. In this study, we illustrate that HCV relies on p7 function for efficient assembly and release of infectious progeny virions from liver cells. Conversely, entry of HCV particles into new host cells is independent of p7. This new evidence supports the recent proposal to include p7 into the family of viroporins that comprises proteins from diverse viruses, for instance, HIV-1 and influenza A virus. Members of this group of functionally related proteins form membrane pores that promote virus release and in some cases also virus entry. Moreover, we identify several conserved p7 residues crucial for functioning of this protein. These amino acids possibly stabilize the structure of p7 or directly participate in channelling of ions. Interestingly, p7 variants from divergent patient isolates differ with regard to their ability to promote virus production, suggesting that p7 modulates viral fitness. Together these observations shed new light on fundamental aspects of the HCV replication strategy.
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Affiliation(s)
- Eike Steinmann
- Department of Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Francois Penin
- Institut de Biologie et Chimie des Protéines, UMR 5086 CNRS, Université Lyon 1, IFR 128 BioSciences Lyon-Gerland, Lyon, France
| | - Stephanie Kallis
- Department of Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Arvind H Patel
- Medical Research Council Virology Unit, Institute of Virology, University of Glasgow, Glasgow, United Kingdom
| | - Ralf Bartenschlager
- Department of Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Thomas Pietschmann
- Department of Molecular Virology, University of Heidelberg, Heidelberg, Germany
- * To whom correspondence should be addressed. E-mail:
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Shelton H, Harris M. Hepatitis C virus NS5A protein binds the SH3 domain of the Fyn tyrosine kinase with high affinity: mutagenic analysis of residues within the SH3 domain that contribute to the interaction. Virol J 2008; 5:24. [PMID: 18267011 PMCID: PMC2259325 DOI: 10.1186/1743-422x-5-24] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2008] [Accepted: 02/11/2008] [Indexed: 01/24/2023] Open
Abstract
BACKGROUND The hepatitis C virus (HCV) non-structural 5A protein (NS5A) contains a highly conserved C-terminal polyproline motif with the consensus sequence Pro-X-X-Pro-X-Arg that is able to interact with the Src-homology 3 (SH3) domains of a variety of cellular proteins. RESULTS To understand this interaction in more detail we have expressed two N-terminally truncated forms of NS5A in E. coli and examined their interactions with the SH3 domain of the Src-family tyrosine kinase, Fyn. Surface plasmon resonance analysis revealed that NS5A binds to the Fyn SH3 domain with what can be considered a high affinity SH3 domain-ligand interaction (629 nM), and this binding did not require the presence of domain I of NS5A (amino acid residues 32-250). Mutagenic analysis of the Fyn SH3 domain demonstrated the requirement for an acidic cluster at the C-terminus of the RT-Src loop of the SH3 domain, as well as several highly conserved residues previously shown to participate in SH3 domain peptide binding. CONCLUSION We conclude that the NS5A:Fyn SH3 domain interaction occurs via a canonical SH3 domain binding site and the high affinity of the interaction suggests that NS5A would be able to compete with cognate Fyn ligands within the infected cell.
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Affiliation(s)
- Holly Shelton
- Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.
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