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Kumari R, Sharma SD, Kumar A, Ende Z, Mishina M, Wang Y, Falls Z, Samudrala R, Pohl J, Knight PR, Sambhara S. Antiviral Approaches against Influenza Virus. Clin Microbiol Rev 2023; 36:e0004022. [PMID: 36645300 PMCID: PMC10035319 DOI: 10.1128/cmr.00040-22] [Citation(s) in RCA: 20] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Preventing and controlling influenza virus infection remains a global public health challenge, as it causes seasonal epidemics to unexpected pandemics. These infections are responsible for high morbidity, mortality, and substantial economic impact. Vaccines are the prophylaxis mainstay in the fight against influenza. However, vaccination fails to confer complete protection due to inadequate vaccination coverages, vaccine shortages, and mismatches with circulating strains. Antivirals represent an important prophylactic and therapeutic measure to reduce influenza-associated morbidity and mortality, particularly in high-risk populations. Here, we review current FDA-approved influenza antivirals with their mechanisms of action, and different viral- and host-directed influenza antiviral approaches, including immunomodulatory interventions in clinical development. Furthermore, we also illustrate the potential utility of machine learning in developing next-generation antivirals against influenza.
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Affiliation(s)
- Rashmi Kumari
- Immunology and Pathogenesis Branch, Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
- Department of Anesthesiology, Jacobs School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, New York, USA
| | - Suresh D. Sharma
- Immunology and Pathogenesis Branch, Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Amrita Kumar
- Immunology and Pathogenesis Branch, Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Zachary Ende
- Immunology and Pathogenesis Branch, Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
- Oak Ridge Institute for Science and Education (ORISE), CDC Fellowship Program, Oak Ridge, Tennessee, USA
| | - Margarita Mishina
- Immunology and Pathogenesis Branch, Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Yuanyuan Wang
- Biotechnology Core Facility Branch, Division of Scientific Resources, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
- Association of Public Health Laboratories, Silver Spring, Maryland, USA
| | - Zackary Falls
- Department of Biomedical Informatics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, New York, USA
| | - Ram Samudrala
- Department of Biomedical Informatics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, New York, USA
| | - Jan Pohl
- Biotechnology Core Facility Branch, Division of Scientific Resources, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Paul R. Knight
- Department of Anesthesiology, Jacobs School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, New York, USA
| | - Suryaprakash Sambhara
- Immunology and Pathogenesis Branch, Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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Mtambo SE, Amoako DG, Somboro AM, Agoni C, Lawal MM, Gumede NS, Khan RB, Kumalo HM. Influenza Viruses: Harnessing the Crucial Role of the M2 Ion-Channel and Neuraminidase toward Inhibitor Design. Molecules 2021; 26:880. [PMID: 33562349 PMCID: PMC7916051 DOI: 10.3390/molecules26040880] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2021] [Revised: 02/01/2021] [Accepted: 02/01/2021] [Indexed: 12/18/2022] Open
Abstract
As a member of the Orthomyxoviridae family of viruses, influenza viruses (IVs) are known causative agents of respiratory infection in vertebrates. They remain a major global threat responsible for the most virulent diseases and global pandemics in humans. The virulence of IVs and the consequential high morbidity and mortality of IV infections are primarily attributed to the high mutation rates in the IVs' genome coupled with the numerous genomic segments, which give rise to antiviral resistant and vaccine evading strains. Current therapeutic options include vaccines and small molecule inhibitors, which therapeutically target various catalytic processes in IVs. However, the periodic emergence of new IV strains necessitates the continuous development of novel anti-influenza therapeutic options. The crux of this review highlights the recent studies on the biology of influenza viruses, focusing on the structure, function, and mechanism of action of the M2 channel and neuraminidase as therapeutic targets. We further provide an update on the development of new M2 channel and neuraminidase inhibitors as an alternative to existing anti-influenza therapy. We conclude by highlighting therapeutic strategies that could be explored further towards the design of novel anti-influenza inhibitors with the ability to inhibit resistant strains.
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Affiliation(s)
- Sphamadla E. Mtambo
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Daniel G. Amoako
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
- Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, Johannesburg 2131, South Africa
| | - Anou M. Somboro
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
- Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, Johannesburg 2131, South Africa
| | - Clement Agoni
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Monsurat M. Lawal
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Nelisiwe S. Gumede
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Rene B. Khan
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Hezekiel M. Kumalo
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
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A Novel Mechanism Underlying Antiviral Activity of an Influenza Virus M2-Specific Antibody. J Virol 2020; 95:JVI.01277-20. [PMID: 33055251 DOI: 10.1128/jvi.01277-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Accepted: 10/08/2020] [Indexed: 11/20/2022] Open
Abstract
Protective immunity against influenza A viruses (IAVs) generally depends on antibodies to the major envelope glycoprotein, hemagglutinin (HA), whose antigenicity is distinctive among IAV subtypes. On the other hand, the matrix 2 (M2) protein is antigenically highly conserved and has been studied as an attractive vaccine antigen to confer cross-protective immunity against multiple subtypes of IAVs. However, antiviral mechanisms of M2-specific antibodies are not fully understood. Here, we report the molecular basis of antiviral activity of an M2-specific monoclonal antibody (MAb), rM2ss23. We first found that rM2ss23 inhibited A/Aichi/2/1968 (H3N2) (Aichi) but not A/PR/8/1934 (H1N1) (PR8) replication. rM2ss23 altered the cell surface distribution of M2, likely by cross-linking the molecules, and interfered with the colocalization of HA and M2, resulting in reduced budding of progeny viruses. However, these effects were not observed for another strain, PR8, despite the binding capacity of rM2ss23 to PR8 M2. Interestingly, HA was also involved in the resistance of PR8 to rM2ss23. We also found that two amino acid residues at positions 54 and 57 in the M2 cytoplasmic tail were critical for the insensitivity of PR8 to rM2ss2. These findings suggest that the disruption of the M2-HA colocalization on infected cells and subsequent reduction of virus budding is one of the principal mechanisms of antiviral activity of M2-specific antibodies and that anti-M2 antibody-sensitive and -resistant IAVs have different properties in the interaction between M2 and HA.IMPORTANCE Although the IAV HA is the major target of neutralizing antibodies, most of the antibodies are HA subtype specific, restricting the potential of HA-based vaccines. On the contrary, the IAV M2 protein has been studied as a vaccine antigen to confer cross-protective immunity against IAVs with multiple HA subtypes, since M2 is antigenically conserved. Although a number of studies highlight the protective role of anti-HA neutralizing and nonneutralizing antibodies, precise information on the molecular mechanism of action of M2-specific antibodies is still obscure. In this study, we found that an anti-M2 antibody interfered with the HA-M2 association, which is important for efficient budding of progeny virus particles from infected cells. The antiviral activity was IAV strain dependent despite the similar binding capacity of the antibody to M2, and, interestingly, HA was involved in susceptibility to the antibody. Our data provide a novel mechanism underlying antiviral activity of M2-specific antibodies.
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Thomaston JL, Konstantinidi A, Liu L, Lambrinidis G, Tan J, Caffrey M, Wang J, DeGrado WF, Kolocouris A. X-ray Crystal Structures of the Influenza M2 Proton Channel Drug-Resistant V27A Mutant Bound to a Spiro-Adamantyl Amine Inhibitor Reveal the Mechanism of Adamantane Resistance. Biochemistry 2020; 59:627-634. [PMID: 31894969 PMCID: PMC7224692 DOI: 10.1021/acs.biochem.9b00971] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The V27A mutation confers adamantane resistance on the influenza A matrix 2 (M2) proton channel and is becoming more prevalent in circulating populations of influenza A virus. We have used X-ray crystallography to determine structures of a spiro-adamantyl amine inhibitor bound to M2(22-46) V27A and also to M2(21-61) V27A in the Inwardclosed conformation. The spiro-adamantyl amine binding site is nearly identical for the two crystal structures. Compared to the M2 "wild type" (WT) with valine at position 27, we observe that the channel pore is wider at its N-terminus as a result of the V27A mutation and that this removes V27 side chain hydrophobic interactions that are important for binding of amantadine and rimantadine. The spiro-adamantyl amine inhibitor blocks proton conductance in the WT and V27A mutant channels by shifting its binding site in the pore depending on which residue is present at position 27. Additionally, in the structure of the M2(21-61) V27A construct, the C-terminus of the channel is tightly packed relative to that of the M2(22-46) construct. We observe that residues Asp44, Arg45, and Phe48 face the center of the channel pore and would be well-positioned to interact with protons exiting the M2 channel after passing through the His37 gate. A 300 ns molecular dynamics simulation of the M2(22-46) V27A-spiro-adamantyl amine complex predicts with accuracy the position of the ligands and waters inside the pore in the X-ray crystal structure of the M2(22-46) V27A complex.
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Affiliation(s)
- Jessica L. Thomaston
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158, USA
- Membrane Structural and Functional Biology (MS&FB) Group, School of Medicine and School of Biochemistry and Immunology, Trinity College Dublin, Dublin D02 R590, Ireland
| | - Athina Konstantinidi
- Department of Pharmaceutical Chemistry, National and Kapodistrian University of Athens, 15771 Athens, Greece
| | - Lijun Liu
- State Key Laboratory of Chemical Oncogenomics, School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, Shenzhen 518055, China
- DLX Scientific, Lawrence, KS 66049, USA
| | - George Lambrinidis
- Department of Pharmaceutical Chemistry, National and Kapodistrian University of Athens, 15771 Athens, Greece
| | - Jingquan Tan
- Membrane Structural and Functional Biology (MS&FB) Group, School of Medicine and School of Biochemistry and Immunology, Trinity College Dublin, Dublin D02 R590, Ireland
| | - Martin Caffrey
- Membrane Structural and Functional Biology (MS&FB) Group, School of Medicine and School of Biochemistry and Immunology, Trinity College Dublin, Dublin D02 R590, Ireland
| | - Jun Wang
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson, Arizona 85721, USA
| | - William F. DeGrado
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158, USA
| | - Antonios Kolocouris
- Department of Pharmaceutical Chemistry, National and Kapodistrian University of Athens, 15771 Athens, Greece
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Hom N, Gentles L, Bloom JD, Lee KK. Deep Mutational Scan of the Highly Conserved Influenza A Virus M1 Matrix Protein Reveals Substantial Intrinsic Mutational Tolerance. J Virol 2019; 93:e00161-19. [PMID: 31019050 PMCID: PMC6580950 DOI: 10.1128/jvi.00161-19] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Accepted: 04/09/2019] [Indexed: 12/30/2022] Open
Abstract
Influenza A virus matrix protein M1 is involved in multiple stages of the viral infectious cycle. Despite its functional importance, our present understanding of this essential viral protein is limited. The roles of a small subset of specific amino acids have been reported, but a more comprehensive understanding of the relationship between M1 sequence, structure, and virus fitness remains elusive. In this study, we used deep mutational scanning to measure the effect of every amino acid substitution in M1 on viral replication in cell culture. The map of amino acid mutational tolerance we have generated allows us to identify sites that are functionally constrained in cell culture as well as sites that are less constrained. Several sites that exhibit low tolerance to mutation have been found to be critical for M1 function and production of viable virions. Surprisingly, significant portions of the M1 sequence, especially in the C-terminal domain, whose structure is undetermined, were found to be highly tolerant of amino acid variation, despite having extremely low levels of sequence diversity among natural influenza virus strains. This unexpected discrepancy indicates that not all sites in M1 that exhibit high sequence conservation in nature are under strong constraint during selection for viral replication in cell culture.IMPORTANCE The M1 matrix protein is critical for many stages of the influenza virus infection cycle. Currently, we have an incomplete understanding of this highly conserved protein's function and structure. Key regions of M1, particularly in the C terminus of the protein, remain poorly characterized. In this study, we used deep mutational scanning to determine the extent of M1's tolerance to mutation. Surprisingly, nearly two-thirds of the M1 sequence exhibits a high tolerance for substitutions, contrary to the extremely low sequence diversity observed across naturally occurring M1 isolates. Sites with low mutational tolerance were also identified, suggesting that they likely play critical functional roles and are under selective pressure. These results reveal the intrinsic mutational tolerance throughout M1 and shape future inquiries probing the functions of this essential influenza A virus protein.
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Affiliation(s)
- Nancy Hom
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington, USA
| | - Lauren Gentles
- Department of Microbiology, University of Washington, Seattle, Washington, USA
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
| | - Jesse D Bloom
- Department of Microbiology, University of Washington, Seattle, Washington, USA
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
- Howard Hughes Medical Institute, Chevy Chase, Maryland, USA
| | - Kelly K Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington, USA
- Department of Microbiology, University of Washington, Seattle, Washington, USA
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To J, Torres J. Viroporins in the Influenza Virus. Cells 2019; 8:cells8070654. [PMID: 31261944 PMCID: PMC6679168 DOI: 10.3390/cells8070654] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2019] [Revised: 06/21/2019] [Accepted: 06/27/2019] [Indexed: 12/28/2022] Open
Abstract
Influenza is a highly contagious virus that causes seasonal epidemics and unpredictable pandemics. Four influenza virus types have been identified to date: A, B, C and D, with only A–C known to infect humans. Influenza A and B viruses are responsible for seasonal influenza epidemics in humans and are responsible for up to a billion flu infections annually. The M2 protein is present in all influenza types and belongs to the class of viroporins, i.e., small proteins that form ion channels that increase membrane permeability in virus-infected cells. In influenza A and B, AM2 and BM2 are predominantly proton channels, although they also show some permeability to monovalent cations. By contrast, M2 proteins in influenza C and D, CM2 and DM2, appear to be especially selective for chloride ions, with possibly some permeability to protons. These differences point to different biological roles for M2 in types A and B versus C and D, which is also reflected in their sequences. AM2 is by far the best characterized viroporin, where mechanistic details and rationale of its acid activation, proton selectivity, unidirectionality, and relative low conductance are beginning to be understood. The present review summarizes the biochemical and structural aspects of influenza viroporins and discusses the most relevant aspects of function, inhibition, and interaction with the host.
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Affiliation(s)
- Janet To
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore
| | - Jaume Torres
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore.
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Musharrafieh R, Lagarias PI, Ma C, Tan GS, Kolocouris A, Wang J. The L46P mutant confers a novel allosteric mechanism of resistance toward the influenza A virus M2 S31N proton channel blockers. Mol Pharmacol 2019; 96:148-157. [PMID: 31175183 DOI: 10.1124/mol.119.116640] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 05/30/2019] [Indexed: 12/14/2022] Open
Abstract
The Food and Drug Administration-approved influenza A antiviral amantadine inhibits the wild-type (WT) AM2 channel but not the S31N mutant predominantly found in circulating strains. In this study, serial viral passages were applied to select resistance against a newly developed isoxazole-conjugated adamantane inhibitor that targets the AM2 S31N channel. This led to the identification of the novel drug-resistant mutation L46P located outside the drug-binding site, which suggests an allosteric resistance mechanism. Intriguingly, when the L46P mutant was introduced to AM2 WT, the channel remained sensitive toward amantadine inhibition. To elucidate the molecular mechanism, molecular dynamics simulations and binding free energy molecular mechanics-generalized born surface area (MM-GBSA) calculations were performed on WT and mutant channels. It was found that the L46P mutation caused a conformational change in the N terminus of transmembrane residues 22-31 that ultimately broadened the drug-binding site of AM2 S31N inhibitor 4, which spans residues 26-34, but not of AM2 WT inhibitor amantadine, which spans residues 31-34. The MM-GBSA calculations showed stronger binding stability for 4 in complex with AM2 S31N compared with 4 in complex with AM2 S31N/L46P, and equal binding free energies of amantadine in complex with AM2 WT and AM2 L46P. Overall, these results demonstrate a unique allosteric resistance mechanism toward AM2 S31N channel blockers, and the L46P mutant represents the first experimentally confirmed drug-resistant AM2 mutant that is located outside of the pore where drug binds. SIGNIFICANCE STATEMENT: AM2 S31N is a high-profile antiviral drug target, as more than 95% of currently circulating influenza A viruses carry this mutation. Understanding the mechanism of drug resistance is critical in designing the next generation of AM2 S31N channel blockers. Using a previously developed AM2 S31N channel blocker as a chemical probe, this study was the first to identify a novel resistant mutant, L46P. The L46P mutant is located outside of the drug-binding site. Molecular dynamics simulations showed that L46P causes a dilation of drug-binding site between residues 22 and 31, which affects the binding of AM2 S31N channel blockers, but not the AM2 WT inhibitor amantadine.
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Affiliation(s)
- Rami Musharrafieh
- Department of Pharmacology and Toxicology, College of Pharmacy (R.M., C.M., J.W.) and Department of Chemistry and Biochemistry (R.M.), University of Arizona, Tucson, Arizona; Department of Pharmaceutical Chemistry, Faculty of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Greece (P.I.L., A.K.); J. Craig Venter Institute, La Jolla, California (G.S.T.); and Department of Medicine, University of California, San Diego, La Jolla, California (G.S.T.)
| | - Panagiotis I Lagarias
- Department of Pharmacology and Toxicology, College of Pharmacy (R.M., C.M., J.W.) and Department of Chemistry and Biochemistry (R.M.), University of Arizona, Tucson, Arizona; Department of Pharmaceutical Chemistry, Faculty of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Greece (P.I.L., A.K.); J. Craig Venter Institute, La Jolla, California (G.S.T.); and Department of Medicine, University of California, San Diego, La Jolla, California (G.S.T.)
| | - Chunlong Ma
- Department of Pharmacology and Toxicology, College of Pharmacy (R.M., C.M., J.W.) and Department of Chemistry and Biochemistry (R.M.), University of Arizona, Tucson, Arizona; Department of Pharmaceutical Chemistry, Faculty of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Greece (P.I.L., A.K.); J. Craig Venter Institute, La Jolla, California (G.S.T.); and Department of Medicine, University of California, San Diego, La Jolla, California (G.S.T.)
| | - Gene S Tan
- Department of Pharmacology and Toxicology, College of Pharmacy (R.M., C.M., J.W.) and Department of Chemistry and Biochemistry (R.M.), University of Arizona, Tucson, Arizona; Department of Pharmaceutical Chemistry, Faculty of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Greece (P.I.L., A.K.); J. Craig Venter Institute, La Jolla, California (G.S.T.); and Department of Medicine, University of California, San Diego, La Jolla, California (G.S.T.)
| | - Antonios Kolocouris
- Department of Pharmacology and Toxicology, College of Pharmacy (R.M., C.M., J.W.) and Department of Chemistry and Biochemistry (R.M.), University of Arizona, Tucson, Arizona; Department of Pharmaceutical Chemistry, Faculty of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Greece (P.I.L., A.K.); J. Craig Venter Institute, La Jolla, California (G.S.T.); and Department of Medicine, University of California, San Diego, La Jolla, California (G.S.T.)
| | - Jun Wang
- Department of Pharmacology and Toxicology, College of Pharmacy (R.M., C.M., J.W.) and Department of Chemistry and Biochemistry (R.M.), University of Arizona, Tucson, Arizona; Department of Pharmaceutical Chemistry, Faculty of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis-Zografou, Greece (P.I.L., A.K.); J. Craig Venter Institute, La Jolla, California (G.S.T.); and Department of Medicine, University of California, San Diego, La Jolla, California (G.S.T.)
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8
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Thomaston JL, Polizzi NF, Konstantinidi A, Wang J, Kolocouris A, DeGrado WF. Inhibitors of the M2 Proton Channel Engage and Disrupt Transmembrane Networks of Hydrogen-Bonded Waters. J Am Chem Soc 2018; 140:15219-15226. [PMID: 30165017 DOI: 10.1021/jacs.8b06741] [Citation(s) in RCA: 70] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Water-mediated interactions play key roles in drug binding. In protein sites with sparse polar functionality, a small-molecule approach is often viewed as insufficient to achieve high affinity and specificity. Here we show that small molecules can enable potent inhibition by targeting key waters. The M2 proton channel of influenza A is the target of the antiviral drugs amantadine and rimantadine. Structural studies of drug binding to the channel using X-ray crystallography have been limited because of the challenging nature of the target, with the one previously solved crystal structure limited to 3.5 Å resolution. Here we describe crystal structures of amantadine bound to M2 in the Inwardclosed conformation (2.00 Å), rimantadine bound to M2 in both the Inwardclosed (2.00 Å) and Inwardopen (2.25 Å) conformations, and a spiro-adamantyl amine inhibitor bound to M2 in the Inwardclosed conformation (2.63 Å). These X-ray crystal structures of the M2 proton channel with bound inhibitors reveal that ammonium groups bind to water-lined sites that are hypothesized to stabilize transient hydronium ions formed in the proton-conduction mechanism. Furthermore, the ammonium and adamantyl groups of the adamantyl-amine class of drugs are free to rotate in the channel, minimizing the entropic cost of binding. These drug-bound complexes provide the first high-resolution structures of drugs that interact with and disrupt networks of hydrogen-bonded waters that are widely utilized throughout nature to facilitate proton diffusion within proteins.
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Affiliation(s)
- Jessica L Thomaston
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Nicholas F Polizzi
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Athina Konstantinidi
- Department of Pharmaceutical Chemistry , National and Kapodistrian University of Athens , 15771 Athens , Greece
| | - Jun Wang
- Department of Pharmacology and Toxicology, College of Pharmacy , University of Arizona , Tucson , Arizona 85721 , United States
| | - Antonios Kolocouris
- Department of Pharmaceutical Chemistry , National and Kapodistrian University of Athens , 15771 Athens , Greece
| | - William F DeGrado
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
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9
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Abstract
Solid-state nuclear magnetic resonance (SSNMR) spectroscopy elucidates membrane protein structures and dynamics in atomic detail to yield mechanistic insights. By interrogating membrane proteins in phospholipid bilayers that closely resemble biological membranes, SSNMR spectroscopists have revealed ion conduction mechanisms, substrate transport dynamics, and oligomeric interfaces of seven-transmembrane helix proteins. Research has also identified conformational plasticity underlying virus-cell membrane fusions by complex protein machineries, and β-sheet folding and assembly by amyloidogenic proteins bound to lipid membranes. These studies collectively show that membrane proteins exhibit extensive structural plasticity to carry out their functions. Because of the inherent dependence of NMR frequencies on molecular orientations and the sensitivity of NMR frequencies to dynamical processes on timescales from nanoseconds to seconds, SSNMR spectroscopy is ideally suited to elucidate such structural plasticity, local and global conformational dynamics, protein-lipid and protein-ligand interactions, and protonation states of polar residues. New sensitivity-enhancement techniques, resolution enhancement by ultrahigh magnetic fields, and the advent of 3D and 4D correlation NMR techniques are increasingly aiding these mechanistically important structural studies.
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Affiliation(s)
- Venkata S Mandala
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
| | - Jonathan K Williams
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
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10
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Ma C, Wang J. Functional studies reveal the similarities and differences between AM2 and BM2 proton channels from influenza viruses. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:272-280. [PMID: 29106970 DOI: 10.1016/j.bbamem.2017.10.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 10/24/2017] [Accepted: 10/25/2017] [Indexed: 11/30/2022]
Abstract
AM2 and BM2 proton channels are attractive antiviral drug targets due to their essential roles during influenza virus replication. Although both AM2 and BM2 are proton-selective ion channels, they share little sequence similarity except for the HXXXW sequence, which suggests that their proton conductance properties might differ. To test this hypothesis, we applied two-electrode voltage clamp electrophysiological assays to study the specific conductance, leakage current, channel activation, and inhibition of AM2 and BM2 proton channels. It was found that BM2 channel has a higher specific conductance than AM2 channel at pH5.5. Unlike AM2 channel, whose proton conductance is asymmetric (from viral exterior to interior), BM2 channel is capable of conducting proton in both directions. Moreover, BM2 requires a more acidic pH for channel activation than AM2, as revealed by its lower pKa values. Finally, both AM2 and BM2 can be inhibited by Cu(II) and Cu(I). Overall, the results from this side-by-side comparison of AM2 and BM2 channels reveal the structure-function relationships of these two viroporins, and such information might be important for the designing of novel ion channels.
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Affiliation(s)
- Chunlong Ma
- BIO5 Institute, The University of Arizona, Tucson, AZ 85721, United States
| | - Jun Wang
- BIO5 Institute, The University of Arizona, Tucson, AZ 85721, United States; Department of Pharmacology and Toxicology, College of Pharmacy, The University of Arizona, Tucson, AZ 85721, United States.
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11
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XFEL structures of the influenza M2 proton channel: Room temperature water networks and insights into proton conduction. Proc Natl Acad Sci U S A 2017; 114:13357-13362. [PMID: 28835537 DOI: 10.1073/pnas.1705624114] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The M2 proton channel of influenza A is a drug target that is essential for the reproduction of the flu virus. It is also a model system for the study of selective, unidirectional proton transport across a membrane. Ordered water molecules arranged in "wires" inside the channel pore have been proposed to play a role in both the conduction of protons to the four gating His37 residues and the stabilization of multiple positive charges within the channel. To visualize the solvent in the pore of the channel at room temperature while minimizing the effects of radiation damage, data were collected to a resolution of 1.4 Å using an X-ray free-electron laser (XFEL) at three different pH conditions: pH 5.5, pH 6.5, and pH 8.0. Data were collected on the Inwardopen state, which is an intermediate that accumulates at high protonation of the His37 tetrad. At pH 5.5, a continuous hydrogen-bonded network of water molecules spans the vertical length of the channel, consistent with a Grotthuss mechanism model for proton transport to the His37 tetrad. This ordered solvent at pH 5.5 could act to stabilize the positive charges that build up on the gating His37 tetrad during the proton conduction cycle. The number of ordered pore waters decreases at pH 6.5 and 8.0, where the Inwardopen state is less stable. These studies provide a graphical view of the response of water to a change in charge within a restricted channel environment.
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12
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Structural Basis for Asymmetric Conductance of the Influenza M2 Proton Channel Investigated by Solid-State NMR Spectroscopy. J Mol Biol 2017; 429:2192-2210. [PMID: 28535993 DOI: 10.1016/j.jmb.2017.05.015] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Revised: 04/21/2017] [Accepted: 05/16/2017] [Indexed: 12/25/2022]
Abstract
The influenza M2 protein forms an acid-activated proton channel that is essential for virus replication. The transmembrane H37 selects for protons under low external pH while W41 ensures proton conduction only from the N terminus to the C terminus and prevents reverse current under low internal pH. Here, we address the molecular basis for this asymmetric conduction by investigating the structure and dynamics of a mutant channel, W41F, which permits reverse current under low internal pH. Solid-state NMR experiments show that W41F M2 retains the pH-dependent α-helical conformations and tetrameric structure of the wild-type (WT) channel but has significantly altered protonation and tautomeric equilibria at H37. At high pH, the H37 structure is shifted toward the π tautomer and less cationic tetrads, consistent with faster forward deprotonation to the C terminus. At low pH, the mutant channel contains more cationic tetrads than the WT channel, consistent with faster reverse protonation from the C terminus. 15N NMR spectra allow the extraction of four H37 pKas and show that the pKas are more clustered in the mutant channel compared to WT M2. Moreover, binding of the antiviral drug, amantadine, at the N-terminal pore at low pH did not convert all histidines to the neutral state, as seen in WT M2, but left half of all histidines cationic, unambiguously demonstrating C-terminal protonation of H37 in the mutant. These results indicate that asymmetric conduction in WT M2 is due to W41 inhibition of C-terminal acid activation by H37. When Trp is replaced by Phe, protons can be transferred to H37 bidirectionally with distinct rate constants.
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13
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Hu S, Yin L, Mei S, Li J, Xu F, Sun H, Liu X, Cen S, Liang C, Li A, Guo F. BST-2 restricts IAV release and is countered by the viral M2 protein. Biochem J 2017; 474:715-730. [PMID: 28087685 DOI: 10.1042/bcj20160861] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2016] [Revised: 11/09/2016] [Accepted: 01/13/2017] [Indexed: 12/15/2022]
Abstract
BST-2 (tetherin, CD317, and HM1.24) is induced by interferon and restricts virus release by tethering the enveloped viruses to the cell surface. The effect of BST-2 on influenza A virus (IAV) infection has been inconclusive. In the present study, we report that BST-2 diminishes the production of IAV virus-like particles (VLPs) that are generated by viral neuraminidase and hemagglutinin proteins to a much greater degree than it inhibits the production of wild-type IAV particles. This relatively weaker inhibition of IAV is associated with reduction in BST-2 levels, which is caused by the M2 protein that interacts with BST-2 and leads to down-regulation of cell surface BST-2 via the proteasomal pathway. Similarly to the viral antagonist Vpu, M2 also rescues the production of human immunodeficiency virus-1 VLPs and IAV VLPs in the presence of BST-2. Replication of wild-type and the M2-deleted viruses were both inhibited by BST-2, with the M2-deleted IAV being more restricted. These data reveal one mechanism that IAV employs to counter restriction by BST-2.
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Affiliation(s)
- Siqi Hu
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, and Center for AIDS Research, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, PR China
| | - Lijuan Yin
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, and Center for AIDS Research, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, PR China
| | - Shan Mei
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, and Center for AIDS Research, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, PR China
| | - Jian Li
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, and Center for AIDS Research, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, PR China
| | - Fengwen Xu
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, and Center for AIDS Research, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, PR China
| | - Hong Sun
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, and Center for AIDS Research, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, PR China
| | - Xiaoman Liu
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, and Center for AIDS Research, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, PR China
| | - Shan Cen
- Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100005, PR China
| | - Chen Liang
- McGill University AIDS Centre, Lady Davis Institute, Jewish General Hospital, Montreal H3T 1E2, Canada
| | - Ailing Li
- Institute of Microcirculation, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100005, PR China
| | - Fei Guo
- MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, and Center for AIDS Research, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, PR China
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14
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Host Cellular Protein TRAPPC6AΔ Interacts with Influenza A Virus M2 Protein and Regulates Viral Propagation by Modulating M2 Trafficking. J Virol 2016; 91:JVI.01757-16. [PMID: 27795429 PMCID: PMC5165196 DOI: 10.1128/jvi.01757-16] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Accepted: 09/30/2016] [Indexed: 12/30/2022] Open
Abstract
Influenza A virus (IAV) matrix protein 2 (M2) plays multiple roles in the early and late phases of viral infection. Once synthesized, M2 is translocated to the endoplasmic reticulum (ER), travels to the Golgi apparatus, and is sorted at the trans-Golgi network (TGN) for transport to the apical plasma membrane, where it functions in virus budding. We hypothesized that M2 trafficking along with its secretory pathway must be finely regulated, and host factors could be involved in this process. However, no studies examining the role of host factors in M2 posttranslational transport have been reported. Here, we used a yeast two-hybrid (Y2H) system to screen for host proteins that interact with the M2 protein and identified transport protein particle complex 6A (TRAPPC6A) as a potential binding partner. We found that both TRAPPC6A and its N-terminal internal-deletion isoform, TRAPPC6A delta (TRAPPC6AΔ), interact with M2. Truncation and mutation analyses showed that the highly conserved leucine residue at position 96 of M2 is critical for mediating this interaction. The role of TRAPPC6AΔ in the viral life cycle was investigated by the knockdown of endogenous TRAPPC6AΔ with small interfering RNA (siRNA) and by generating a recombinant virus that was unable to interact with TRAPPC6A/TRAPPC6AΔ. The results indicated that TRAPPC6AΔ, through its interaction with M2, slows M2 trafficking to the apical plasma membrane, favors viral replication in vitro, and positively modulates virus virulence in mice. IMPORTANCE The influenza A virus M2 protein regulates the trafficking of not only other proteins but also itself along the secretory pathway. However, the host factors involved in the regulation of the posttranslational transport of M2 are largely unknown. In this study, we identified TRAPPC6A and its N-terminal internal-deletion isoform, TRAPPC6AΔ, as interacting partners of M2. We found that the leucine (L) residue at position 96 of M2 is critical for mediating this interaction, which leads us to propose that the high level of conservation of 96L is a consequence of M2 adaptation to its interacting host factor TRAPPC6A/TRAPPC6AΔ. Importantly, we discovered that TRAPPC6AΔ can positively regulate viral replication in vitro by modulating M2 trafficking to the plasma membrane.
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15
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Kwon B, Hong M. The Influenza M2 Ectodomain Regulates the Conformational Equilibria of the Transmembrane Proton Channel: Insights from Solid-State Nuclear Magnetic Resonance. Biochemistry 2016; 55:5387-97. [PMID: 27571210 PMCID: PMC5257201 DOI: 10.1021/acs.biochem.6b00727] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The influenza M2 protein is the target of the amantadine family of antiviral drugs, and its transmembrane (TM) domain structure and dynamics have been extensively studied. However, little is known about the structure of the highly conserved N-terminal ectodomain, which contains epitopes targeted by influenza vaccines. In this study, we synthesized an M2 construct containing the N-terminal ectodomain and the TM domain, to understand the site-specific conformation and dynamics of the ectodomain and to investigate the effect of the ectodomain on the TM structure. We incorporated (13)C- and (15)N-labeled residues into both domains and measured their chemical shifts and line widths using solid-state nuclear magnetic resonance. The data indicate that the entire ectodomain is unstructured and dynamic, but the motion is slower for residues closer to the TM domain. (13)C line shapes indicate that this ecto-TM construct undergoes fast uniaxial rotational diffusion, like the isolated TM peptide, but drug binding increases the motional rates of the TM helix while slowing the local motion of the ectodomain residues that are close to the TM domain. Moreover, (13)C and (15)N chemical shifts indicate that the ectodomain shifts the conformational equilibria of the TM residues toward the drug-bound state even in the absence of amantadine, thus providing a molecular structural basis for the lower inhibitory concentration of full-length M2 compared to that of the ectodomain-truncated M2. We propose that this conformational selection may result from electrostatic repulsion between negatively charged ectodomain residues in the tetrameric protein. Together with the recent study of the M2 cytoplasmic domain, these results show that intrinsically disordered extramembrane domains in membrane proteins can regulate the functionally relevant conformation and dynamics of the structurally ordered TM domains.
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Affiliation(s)
- Byungsu Kwon
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 United States
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 United States
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16
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Epitope Mapping of Avian Influenza M2e Protein: Different Species Recognise Various Epitopes. PLoS One 2016; 11:e0156418. [PMID: 27362795 PMCID: PMC4928777 DOI: 10.1371/journal.pone.0156418] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Accepted: 05/14/2016] [Indexed: 12/12/2022] Open
Abstract
A common approach for developing diagnostic tests for influenza virus detection is the use of mouse or rabbit monoclonal and/or polyclonal antibodies against a target antigen of the virus. However, comparative mapping of the target antigen using antibodies from different animal sources has not been evaluated before. This is important because identification of antigenic determinants of the target antigen in different species plays a central role to ensure the efficiency of a diagnostic test, such as competitive ELISA or immunohistochemistry-based tests. Interest in the matrix 2 ectodomain (M2e) protein of avian influenza virus (AIV) as a candidate for a universal vaccine and also as a marker for detection of virus infection in vaccinated animals (DIVA) is the rationale for the selection of this protein for comparative mapping evaluation. This study aimed to map the epitopes of the M2e protein of avian influenza virus H5N1 using chicken, mouse and rabbit monoclonal or monospecific antibodies. Our findings revealed that rabbit antibodies (rAbs) recognized epitope 6EVETPTRN13 of the M2e, located at the N-terminal of the protein, while mouse (mAb) and chicken antibodies (cAbs) recognized epitope 10PTRNEWECK18, located at the centre region of the protein. The findings highlighted the difference between the M2e antigenic determinants recognized by different species that emphasized the importance of comparative mapping of antibody reactivity from different animals to the same antigen, especially in the case of multi-host infectious agents such as influenza. The findings are of importance for antigenic mapping, as well as diagnostic test and vaccine development.
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17
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Mbewana S, Mortimer E, Pêra FFPG, Hitzeroth II, Rybicki EP. Production of H5N1 Influenza Virus Matrix Protein 2 Ectodomain Protein Bodies in Tobacco Plants and in Insect Cells as a Candidate Universal Influenza Vaccine. Front Bioeng Biotechnol 2015; 3:197. [PMID: 26697423 PMCID: PMC4672040 DOI: 10.3389/fbioe.2015.00197] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 11/23/2015] [Indexed: 11/13/2022] Open
Abstract
The spread of influenza A viruses is partially controlled and prevented by vaccination. The matrix protein 2 ectodomain (M2e) is the most conserved sequence in influenza A viruses, and is therefore a good potential target for a vaccine to protect against multiple virus subtypes. We explored the feasibility of an M2e-based universal influenza A vaccine candidate based on the highly pathogenic avian influenza A virus, H5N1. A synthetic M2e gene was human- and plant-codon optimized and fused in-frame with a sequence encoding the N-terminal proline-rich domain (Zera(®)) of the γ-zein protein of maize. Zera(®)M2e was expressed transiently in Nicotiana benthamiana and Sf21 baculovirus/insect cell expression systems, and Zera(®)M2e protein bodies (PBs) were successfully produced in both expression systems. The plant-produced Zera(®)M2e PBs were purified and injected into Balb/c mice. Western blot analysis using insect cell-produced Zera(®)M2e PBs and multiple tandem M2e sequences (5xM2e) fused with the avian influenza H5N1 transmembrane and cytosolic tail (5xM2e_tHA) confirmed the presence of M2e-specific antibodies in immunized mice sera. The immunogenicity of the Zera(®)M2e indicates that our plant-produced protein has potential as an inexpensive universal influenza A vaccine.
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Affiliation(s)
- Sandiswa Mbewana
- Biopharming Research Unit, Department of Molecular and Cell Biology, University of Cape Town , Rondebosch , South Africa
| | - Elizabeth Mortimer
- Biopharming Research Unit, Department of Molecular and Cell Biology, University of Cape Town , Rondebosch , South Africa
| | - Francisco F P G Pêra
- Biopharming Research Unit, Department of Molecular and Cell Biology, University of Cape Town , Rondebosch , South Africa
| | - Inga Isabel Hitzeroth
- Biopharming Research Unit, Department of Molecular and Cell Biology, University of Cape Town , Rondebosch , South Africa
| | - Edward P Rybicki
- Biopharming Research Unit, Department of Molecular and Cell Biology, University of Cape Town , Rondebosch , South Africa ; Institute of Infectious Disease and Molecular Medicine, Faculty of Heath Science, University of Cape Town , Cape Town , South Africa
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18
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Largo E, Verdiá-Báguena C, Aguilella VM, Nieva JL, Alcaraz A. Ion channel activity of the CSFV p7 viroporin in surrogates of the ER lipid bilayer. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1858:30-7. [PMID: 26464198 PMCID: PMC7094309 DOI: 10.1016/j.bbamem.2015.10.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Revised: 10/08/2015] [Accepted: 10/09/2015] [Indexed: 12/22/2022]
Affiliation(s)
- Eneko Largo
- Biophysics Unit (CSIC, UPV/EHU), Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain
| | - Carmina Verdiá-Báguena
- Laboratory of Molecular Biophysics, Department of Physics, University Jaume I, 12071 Castellón, Spain
| | - Vicente M Aguilella
- Laboratory of Molecular Biophysics, Department of Physics, University Jaume I, 12071 Castellón, Spain
| | - José L Nieva
- Biophysics Unit (CSIC, UPV/EHU), Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain
| | - Antonio Alcaraz
- Laboratory of Molecular Biophysics, Department of Physics, University Jaume I, 12071 Castellón, Spain.
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19
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Martinez-Gil L, Mingarro I. Viroporins, Examples of the Two-Stage Membrane Protein Folding Model. Viruses 2015; 7:3462-82. [PMID: 26131957 PMCID: PMC4517110 DOI: 10.3390/v7072781] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2015] [Revised: 06/15/2015] [Accepted: 06/17/2015] [Indexed: 12/21/2022] Open
Abstract
Viroporins are small, α-helical, hydrophobic virus encoded proteins, engineered to form homo-oligomeric hydrophilic pores in the host membrane. Viroporins participate in multiple steps of the viral life cycle, from entry to budding. As any other membrane protein, viroporins have to find the way to bury their hydrophobic regions into the lipid bilayer. Once within the membrane, the hydrophobic helices of viroporins interact with each other to form higher ordered structures required to correctly perform their porating activities. This two-step process resembles the two-stage model proposed for membrane protein folding by Engelman and Poppot. In this review we use the membrane protein folding model as a leading thread to analyze the mechanism and forces behind the membrane insertion and folding of viroporins. We start by describing the transmembrane segment architecture of viroporins, including the number and sequence characteristics of their membrane-spanning domains. Next, we connect the differences found among viroporin families to their viral genome organization, and finalize focusing on the pathways used by viroporins in their way to the membrane and on the transmembrane helix-helix interactions required to achieve proper folding and assembly.
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Affiliation(s)
- Luis Martinez-Gil
- Department of Biochemistry and Molecular Biology, ERI BioTecMed, University of Valencia, Dr. Moliner 50, 46100 Burjassot, Spain.
| | - Ismael Mingarro
- Department of Biochemistry and Molecular Biology, ERI BioTecMed, University of Valencia, Dr. Moliner 50, 46100 Burjassot, Spain.
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20
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Vasin AV, Temkina OA, Egorov VV, Klotchenko SA, Plotnikova MA, Kiselev OI. Molecular mechanisms enhancing the proteome of influenza A viruses: an overview of recently discovered proteins. Virus Res 2014; 185:53-63. [PMID: 24675275 DOI: 10.1016/j.virusres.2014.03.015] [Citation(s) in RCA: 118] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Revised: 02/19/2014] [Accepted: 03/11/2014] [Indexed: 12/11/2022]
Abstract
Influenza A virus is one of the major human pathogens. Despite numerous efforts to produce absolutely effective anti-influenza drugs or vaccines, no such agent has been developed yet. One of the main reasons for this complication is the high mutation rate and the specific structure of influenza A viruses genome. For more than 25 years since the first mapping of the viral genome, it was believed that its 8 genome segments encode 10 proteins. However, the proteome of influenza A viruses has turned out to be much more complex than previously thought. In 2001, the first accessory protein, PB1-F2, translated from the alternative open reading frame, was discovered. Subsequently, six more proteins, PB1-N40, PA-X, PA-N155, PA-N182, M42, and NS3, have been found. It is important to pay close attention to these novel proteins in order to evaluate their role in the pathogenesis of influenza, especially in the case of outbreaks of human infections with new avian viruses, such as H5N1 or H7N9. In this review we summarize the data on the molecular mechanisms used by influenza A viruses to expand their proteome and on the possible functions of the recently discovered viral proteins.
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Affiliation(s)
- A V Vasin
- Laboratory of Structural and Functional Proteomics, Research Institute of Influenza, St-Petersburg 197376, Russia.
| | - O A Temkina
- Laboratory of Structural and Functional Proteomics, Research Institute of Influenza, St-Petersburg 197376, Russia
| | - V V Egorov
- Laboratory of Structural and Functional Proteomics, Research Institute of Influenza, St-Petersburg 197376, Russia
| | - S A Klotchenko
- Laboratory of Structural and Functional Proteomics, Research Institute of Influenza, St-Petersburg 197376, Russia
| | - M A Plotnikova
- Laboratory of Structural and Functional Proteomics, Research Institute of Influenza, St-Petersburg 197376, Russia
| | - O I Kiselev
- Laboratory of Structural and Functional Proteomics, Research Institute of Influenza, St-Petersburg 197376, Russia
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21
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Liao SY, Fritzsching KJ, Hong M. Conformational analysis of the full-length M2 protein of the influenza A virus using solid-state NMR. Protein Sci 2013; 22:1623-38. [PMID: 24023039 DOI: 10.1002/pro.2368] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Revised: 09/04/2013] [Accepted: 09/04/2013] [Indexed: 12/24/2022]
Abstract
The influenza A M2 protein forms a proton channel for virus infection and mediates virus assembly and budding. While extensive structural information is known about the transmembrane helix and an adjacent amphipathic helix, the conformation of the N-terminal ectodomain and the C-terminal cytoplasmic tail remains largely unknown. Using two-dimensional (2D) magic-angle-spinning solid-state NMR, we have investigated the secondary structure and dynamics of full-length M2 (M2FL) and found them to depend on the membrane composition. In 2D (13)C DARR correlation spectra, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)-bound M2FL exhibits several peaks at β-sheet chemical shifts, which result from water-exposed extramembrane residues. In contrast, M2FL bound to cholesterol-containing membranes gives predominantly α-helical chemical shifts. Two-dimensional J-INADEQUATE spectra and variable-temperature (13)C spectra indicate that DMPC-bound M2FL is highly dynamic while the cholesterol-containing membranes significantly immobilize the protein at physiological temperature. Chemical-shift prediction for various secondary-structure models suggests that the β-strand is located at the N-terminus of the DMPC-bound protein, while the cytoplasmic domain is unstructured. This prediction is confirmed by the 2D DARR spectrum of the ectodomain-truncated M2(21-97), which no longer exhibits β-sheet chemical shifts in the DMPC-bound state. We propose that the M2 conformational change results from the influence of cholesterol, and the increased helicity of M2FL in cholesterol-rich membranes may be relevant for M2 interaction with the matrix protein M1 during virus assembly and budding. The successful determination of the β-strand location suggests that chemical-shift prediction is a promising approach for obtaining structural information of disordered proteins before resonance assignment.
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Affiliation(s)
- Shu Yu Liao
- Department of Chemistry, Iowa State University, Ames, Iowa, 50011
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22
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Wise HM, Hutchinson EC, Jagger BW, Stuart AD, Kang ZH, Robb N, Schwartzman LM, Kash JC, Fodor E, Firth AE, Gog JR, Taubenberger JK, Digard P. Identification of a novel splice variant form of the influenza A virus M2 ion channel with an antigenically distinct ectodomain. PLoS Pathog 2012; 8:e1002998. [PMID: 23133386 PMCID: PMC3486900 DOI: 10.1371/journal.ppat.1002998] [Citation(s) in RCA: 165] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Accepted: 09/13/2012] [Indexed: 01/25/2023] Open
Abstract
Segment 7 of influenza A virus produces up to four mRNAs. Unspliced transcripts encode M1, spliced mRNA2 encodes the M2 ion channel, while protein products from spliced mRNAs 3 and 4 have not previously been identified. The M2 protein plays important roles in virus entry and assembly, and is a target for antiviral drugs and vaccination. Surprisingly, M2 is not essential for virus replication in a laboratory setting, although its loss attenuates the virus. To better understand how IAV might replicate without M2, we studied the reversion mechanism of an M2-null virus. Serial passage of a virus lacking the mRNA2 splice donor site identified a single nucleotide pseudoreverting mutation, which restored growth in cell culture and virulence in mice by upregulating mRNA4 synthesis rather than by reinstating mRNA2 production. We show that mRNA4 encodes a novel M2-related protein (designated M42) with an antigenically distinct ectodomain that can functionally replace M2 despite showing clear differences in intracellular localisation, being largely retained in the Golgi compartment. We also show that the expression of two distinct ion channel proteins is not unique to laboratory-adapted viruses but, most notably, was also a feature of the 1983 North American outbreak of H5N2 highly pathogenic avian influenza virus. In identifying a 14th influenza A polypeptide, our data reinforce the unexpectedly high coding capacity of the viral genome and have implications for virus evolution, as well as for understanding the role of M2 in the virus life cycle. Influenza A virus is a pathogen capable of infecting a wide range of avian and mammalian hosts, causing seasonal epidemics and pandemics in humans. In recent years, the unexpected coding capacity of the virus has begun to be unravelled, with the identification of three more protein products (PB1-F2, PB1-N40 and PA-X) on top of the 10 viral proteins originally identified 30 years ago. Here, we identify a 14th primary translation product, made from segment 7. Previously established protein products from segment 7 include the matrix (M1) and ion channel (M2) proteins. M2, made from a spliced transcript, has multiple roles in the virus lifecycle including in entry and budding. In a laboratory setting, it is possible to generate M2 deficient viruses, but these are highly attenuated. However, upon serial passage a virus lacking the M2 splice donor site quickly recovered wild type growth properties, without reverting the original mutation. Instead we found a compensatory single nucleotide mutation had upregulated another segment 7 mRNA. This mRNA encoded a novel M2-like protein with a variant extracellular domain, which we called M42. M42 compensated for loss of M2 in tissue culture cells and animals, although it displayed some differences in subcellular localisation. Our study therefore identifies a further novel influenza protein and gives insights into the evolution of the virus.
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MESH Headings
- Alternative Splicing
- Animals
- Birds
- Cell Line, Tumor
- Disease Outbreaks
- Dogs
- Humans
- Influenza A Virus, H5N2 Subtype/genetics
- Influenza A Virus, H5N2 Subtype/metabolism
- Influenza in Birds/epidemiology
- Influenza in Birds/genetics
- Influenza in Birds/metabolism
- Influenza, Human/epidemiology
- Influenza, Human/genetics
- Influenza, Human/metabolism
- Mice
- Mice, Inbred BALB C
- North America/epidemiology
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- RNA, Viral/biosynthesis
- RNA, Viral/genetics
- Viral Matrix Proteins/biosynthesis
- Viral Matrix Proteins/genetics
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Affiliation(s)
- Helen M. Wise
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom
- The Roslin Institute, University of Edinburgh, Easter Bush, Midlothian, United Kingdom
| | - Edward C. Hutchinson
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Brett W. Jagger
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom
- Viral Pathogenesis and Evolution Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Amanda D. Stuart
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Zi H. Kang
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Nicole Robb
- Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Louis M. Schwartzman
- Viral Pathogenesis and Evolution Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - John C. Kash
- Viral Pathogenesis and Evolution Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Ervin Fodor
- Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Andrew E. Firth
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Julia R. Gog
- DAMTP, Centre for Mathematical Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Jeffery K. Taubenberger
- Viral Pathogenesis and Evolution Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Paul Digard
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom
- The Roslin Institute, University of Edinburgh, Easter Bush, Midlothian, United Kingdom
- * E-mail:
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23
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Hong M, DeGrado WF. Structural basis for proton conduction and inhibition by the influenza M2 protein. Protein Sci 2012; 21:1620-33. [PMID: 23001990 DOI: 10.1002/pro.2158] [Citation(s) in RCA: 111] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Revised: 09/10/2012] [Accepted: 09/11/2012] [Indexed: 12/20/2022]
Abstract
The influenza M2 protein forms an acid-activated and drug-sensitive proton channel in the virus envelope that is important for the virus lifecycle. The functional properties and high-resolution structures of this proton channel have been extensively studied to understand the mechanisms of proton conduction and drug inhibition. We review biochemical and electrophysiological studies of M2 and discuss how high-resolution structures have transformed our understanding of this proton channel. Comparison of structures obtained in different membrane-mimetic solvents and under different pH using X-ray crystallography, solution NMR, and solid-state NMR spectroscopy revealed how the M2 structure depends on the environment and showed that the pharmacologically relevant drug-binding site lies in the transmembrane (TM) pore. Competing models of proton conduction have been evaluated using biochemical experiments, high-resolution structural methods, and computational modeling. These results are converging to a model in which a histidine residue in the TM domain mediates proton relay with water, aided by microsecond conformational dynamics of the imidazole ring. These mechanistic insights are guiding the design of new inhibitors that target drug-resistant M2 variants and may be relevant for other proton channels.
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Affiliation(s)
- Mei Hong
- Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
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24
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Hashemi H, Pouyanfard S, Bandehpour M, Noroozbabaei Z, Kazemi B, Saelens X, Mokhtari-Azad T. Immunization with M2e-displaying T7 bacteriophage nanoparticles protects against influenza A virus challenge. PLoS One 2012; 7:e45765. [PMID: 23029232 PMCID: PMC3454340 DOI: 10.1371/journal.pone.0045765] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Accepted: 08/23/2012] [Indexed: 12/17/2022] Open
Abstract
Considering the emergence of highly pathogenic influenza viruses and threat of worldwide pandemics, there is an urgent need to develop broadly-protective influenza vaccines. In this study, we demonstrate the potential of T7 bacteriophage-based nanoparticles with genetically fused ectodomain of influenza A virus M2 protein (T7-M2e) as a candidate universal flu vaccine. Immunization of mice with non-adjuvanted T7-M2e elicited M2e-specific serum antibody responses that were similar in magnitude to those elicited by M2e peptide administered in Freund’s adjuvant. Comparable IgG responses directed against T7 phage capsomers were induced following vaccination with wild type T7 or T7-M2e. T7-M2e immunization induced balanced amounts of IgG1 and IgG2a antibodies and these antibodies specifically recognized native M2 on the surface of influenza A virus-infected mammalian cells. The frequency of IFN-γ-secreting T cells induced by T7-M2e nanoparticles was comparable to those elicited by M2e peptide emulsified in Freund’s adjuvant. Emulsification of T7-M2e nanoparticles in Freund’s adjuvant, however, induced a significantly stronger T cell response. Furthermore, T7-M2e-immunized mice were protected against lethal challenge with an H1N1 or an H3N2 virus, implying the induction of hetero-subtypic immunity in our mouse model. T7-M2e-immunized mice displayed considerable weight loss and had significantly reduced viral load in their lungs compared to controls. We conclude that display of M2e on the surface of T7 phage nanoparticles offers an efficient and economical opportunity to induce cross-protective M2e-based immunity against influenza A.
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Affiliation(s)
- Hamidreza Hashemi
- Department of Virology, Tehran University of Medical Sciences, Tehran, Iran
| | | | - Mojgan Bandehpour
- Cellular and Molecular Biology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
- Biotechnology Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Zahra Noroozbabaei
- Department of Virology, Tehran University of Medical Sciences, Tehran, Iran
| | - Bahram Kazemi
- Cellular and Molecular Biology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
- Biotechnology Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
- * E-mail: (BK); (TM)
| | - Xavier Saelens
- Department for Molecular Biomedical Research, VIB, Ghent, Belgium
- Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium
| | - Talat Mokhtari-Azad
- Department of Virology, Tehran University of Medical Sciences, Tehran, Iran
- * E-mail: (BK); (TM)
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25
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Grigoryan G, Moore DT, DeGrado WF. Transmembrane communication: general principles and lessons from the structure and function of the M2 proton channel, K⁺ channels, and integrin receptors. Annu Rev Biochem 2011; 80:211-37. [PMID: 21548783 DOI: 10.1146/annurev-biochem-091008-152423] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Signal transduction across biological membranes is central to life. This process generally happens through communication between different domains and hierarchical coupling of information. Here, we review structural and thermodynamic principles behind transmembrane (TM) signal transduction and discuss common themes. Communication between signaling domains can be understood in terms of thermodynamic and kinetic principles, and complex signaling patterns can arise from simple wiring of thermodynamically coupled domains. We relate this to functions of several signal transduction systems: the M2 proton channel from influenza A virus, potassium channels, integrin receptors, and bacterial kinases. We also discuss key features in the structural rearrangements responsible for signal transduction in these systems.
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Affiliation(s)
- Gevorg Grigoryan
- Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
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26
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Cady SD, Wang J, Wu Y, DeGrado WF, Hong M. Specific binding of adamantane drugs and direction of their polar amines in the pore of the influenza M2 transmembrane domain in lipid bilayers and dodecylphosphocholine micelles determined by NMR spectroscopy. J Am Chem Soc 2011; 133:4274-84. [PMID: 21381693 PMCID: PMC3078525 DOI: 10.1021/ja102581n] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The transmembrane domain of the influenza M2 protein (M2TM) forms a tetrameric proton channel important for the virus lifecycle. The proton-channel activity is inhibited by amine-containing adamantyl drugs amantadine and rimantadine, which have been shown to bind specifically to the pore of M2TM near Ser31. However, whether the polar amine points to the N- or C-terminus of the channel has not yet been determined. Elucidating the polar group direction will shed light on the mechanism by which drug binding inhibits this proton channel and will facilitate rational design of new inhibitors. In this study, we determine the polar amine direction using M2TM reconstituted in lipid bilayers as well as dodecylphosphocholine (DPC) micelles. (13)C-(2)H rotational-echo double-resonance NMR experiments of (13)C-labeled M2TM and methyl-deuterated rimantadine in lipid bilayers showed that the polar amine pointed to the C-terminus of the channel, with the methyl group close to Gly34. Solution NMR experiments of M2TM in DPC micelles indicate that drug binding causes significant chemical shift perturbations of the protein that are very similar to those seen for M2TM and M2(18-60) bound to lipid bilayers. Specific (2)H-labeling of the drugs permitted the assignment of drug-protein cross peaks, which indicate that amantadine and rimantadine bind to the pore in the same fashion as for bilayer-bound M2TM. These results strongly suggest that adamantyl inhibition of M2TM is achieved not only by direct physical occlusion of the channel, but also by perturbing the equilibrium constant of the proton-sensing residue His37. The reproduction of the pharmacologically relevant specific pore-binding site in DPC micelles, which was not observed with a different detergent, DHPC, underscores the significant influence of the detergent environment on the functional structure of this membrane protein.
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Affiliation(s)
- Sarah D. Cady
- Department of Chemistry, Iowa State University, Ames, IA 50011
| | - Jun Wang
- Department of Biochemistry & Biophysics, School of Medicine, and Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104–6059
| | - Yibing Wu
- Department of Biochemistry & Biophysics, School of Medicine, and Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104–6059
| | - William F. DeGrado
- Department of Biochemistry & Biophysics, School of Medicine, and Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104–6059
| | - Mei Hong
- Department of Chemistry, Iowa State University, Ames, IA 50011
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27
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Wang J, Qiu JX, Soto C, DeGrado WF. Structural and dynamic mechanisms for the function and inhibition of the M2 proton channel from influenza A virus. Curr Opin Struct Biol 2011; 21:68-80. [PMID: 21247754 PMCID: PMC3039100 DOI: 10.1016/j.sbi.2010.12.002] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Accepted: 12/09/2010] [Indexed: 12/11/2022]
Abstract
The M2 proton channel from influenza A virus, a prototype for a class of viral ion channels known as viroporins, conducts protons along a chain of water molecules and ionizable sidechains, including His37. Recent studies highlight a delicate interplay between protein folding, proton binding, and proton conduction through the channel. Drugs inhibit proton conduction by binding to an aqueous cavity adjacent to M2's proton-selective filter, thereby blocking access of proton to the filter, and altering the energetic landscape of the channel and the energetics of proton-binding to His37.
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Affiliation(s)
- Jun Wang
- Department of Chemistry, School of Medicine, University of Pennsylvania, 422 Curvie Blvd, Philadelphia, PA, 19104, USA
| | - Jade Xiaoyan Qiu
- Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, 422 Curvie Blvd, Philadelphia, PA, 19104, USA
| | - Cinque Soto
- Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, 422 Curvie Blvd, Philadelphia, PA, 19104, USA
| | - William F. DeGrado
- Department of Chemistry, School of Medicine, University of Pennsylvania, 422 Curvie Blvd, Philadelphia, PA, 19104, USA
- Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, 422 Curvie Blvd, Philadelphia, PA, 19104, USA
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28
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Mi S, Li Y, Yan J, Gao GF. Na(+)/K (+)-ATPase β1 subunit interacts with M2 proteins of influenza A and B viruses and affects the virus replication. SCIENCE CHINA-LIFE SCIENCES 2010; 53:1098-105. [PMID: 21104370 DOI: 10.1007/s11427-010-4048-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2010] [Accepted: 07/04/2010] [Indexed: 01/23/2023]
Abstract
Interplay between the host and influenza virus has a pivotal role for the outcome of infection. The matrix proteins M2/BM2 from influenza (A and B) viruses are small type III integral membrane proteins with a single transmembrane domain, a short amino-terminal ectodomain and a long carboxy-terminal cytoplasmic domain. They function as proton channels, mainly forming a membrane-spanning pore through the transmembrane domain tetramer, and are essential for virus assembly and release of the viral genetic materials in the endosomal fusion process. However, little is known about the host factors which interact with M2/BM2 proteins and the functions of the long cytoplasmic domain are currently unknown. Starting with yeast two-hybrid screening and applying a series of experiments we identified that the β1 subunit of the host Na(+)/K(+)-ATPase β1 subunit (ATP1B1) interacts with the cytoplasmic domain of both the M2 and BM2 proteins. A stable ATP1B1 knockdown MDCK cell line was established and we showed that the ATP1B1 knockdown suppressed influenza virus A/WSN/33 replication, implying that the interaction is crucial for influenza virus replication in the host cell. We propose that influenza virus M2/BM2 cytoplasmic domain has an important role in the virus-host interplay and facilitates virus replication.
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Affiliation(s)
- ShuoFu Mi
- CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China
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29
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Stewart SM, Wu WH, Lalime EN, Pekosz A. The cholesterol recognition/interaction amino acid consensus motif of the influenza A virus M2 protein is not required for virus replication but contributes to virulence. Virology 2010; 405:530-8. [PMID: 20655564 PMCID: PMC2923277 DOI: 10.1016/j.virol.2010.06.035] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Revised: 08/27/2009] [Accepted: 06/18/2010] [Indexed: 12/21/2022]
Abstract
Influenza A virus particles assemble and bud from plasma membrane domains enriched with the viral glycoproteins but only a small fraction of the total M2 protein is incorporated into virus particles when compared to the other viral glycoproteins. A membrane proximal cholesterol recognition/interaction amino acid consensus (CRAC) motif was previously identified in M2 and suggested to play a role in protein function. We investigated the importance of the CRAC motif on virus replication by generating recombinant proteins and viruses containing amino acid substitutions in this motif. Alteration or completion of the M2 CRAC motif in two different virus strains caused no changes in virus replication in vitro. Viruses lacking an M2 CRAC motif had decreased morbidity and mortality in the mouse model of infection, suggesting that this motif is a virulence determinant which may facilitate virus replication in vivo but is not required for basic virus replication in tissue culture.
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Affiliation(s)
- Shaun M Stewart
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University, Bloomberg School of Public Health, 615 North Wolfe St Suite 5132, Baltimore MD 21205
- Division of Biology and Biomedical Sciences, Washington University in St. Louis, Campus Box 8226, 660 South Euclid St, St. Louis, MO 63110
| | - Wai-Hong Wu
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University, Bloomberg School of Public Health, 615 North Wolfe St Suite 5132, Baltimore MD 21205
| | - Erin N Lalime
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University, Bloomberg School of Public Health, 615 North Wolfe St Suite 5132, Baltimore MD 21205
| | - Andrew Pekosz
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University, Bloomberg School of Public Health, 615 North Wolfe St Suite 5132, Baltimore MD 21205
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30
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Cross TA, Sharma M, Yi M, Zhou HX. Influence of solubilizing environments on membrane protein structures. Trends Biochem Sci 2010; 36:117-25. [PMID: 20724162 DOI: 10.1016/j.tibs.2010.07.005] [Citation(s) in RCA: 159] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Revised: 07/02/2010] [Accepted: 07/13/2010] [Indexed: 12/21/2022]
Abstract
Membrane protein structures are stabilized by weak interactions and are influenced by additional interactions with the solubilizing environment. Structures of influenza virus A M2 protein, a proven drug target, have been determined in three different environments, thus providing a unique opportunity to assess environmental influences. Structures determined in detergents and detergent micelles can have notable differences from those determined in lipid bilayers. These differences make it imperative to validate membrane protein structures.
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Affiliation(s)
- Timothy A Cross
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA.
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31
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Pejoski D, Zeng W, Rockman S, Brown LE, Jackson DC. A lipopeptide based on the M2 and HA proteins of influenza A viruses induces protective antibody. Immunol Cell Biol 2010; 88:605-11. [PMID: 20177411 DOI: 10.1038/icb.2010.15] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A conserved 15 amino-acid residue sequence of the ectodomain of the M2 protein of influenza A virus (M2e) induces a strong antibody (Ab) response when incorporated into a synthetic lipopeptide vaccine candidate containing a T-helper epitope from influenza A hemagglutinin and the dendritic cell-targeting lipid moiety S-[2,3-bis(palmitoyloxy)propyl]cysteine (Pam2Cys). Abs elicited by the truncated M2e sequence were specific for the M2 protein of influenza A virus and were also capable of binding to cells that were infected with influenza A viruses of different subtypes. The Ab titres against the lipopeptide were similar in magnitude to those elicited by the full-length (23 residue) M2e peptide when administered in Freund's adjuvant. Abs to the truncated M2e sequence were also able to significantly reduce the viral load in airways of BALB/c mice after challenge with live influenza virus.
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Affiliation(s)
- David Pejoski
- Department of Microbiology and Immunology, The University of Melbourne, Parkville, Victoria, Australia
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32
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Abstract
Up to now less than a handful of viral cholesterol-binding proteins have been characterized, in HIV, influenza virus and Semliki Forest virus. These are proteins with roles in virus entry or morphogenesis. In the case of the HIV fusion protein gp41 cholesterol binding is attributed to a cholesterol recognition consensus (CRAC) motif in a flexible domain of the ectodomain preceding the trans-membrane segment. This specific CRAC sequence mediates gp41 binding to a cholesterol affinity column. Mutations in this motif arrest virus fusion at the hemifusion stage and modify the ability of the isolated CRAC peptide to induce segregation of cholesterol in artificial membranes.Influenza A virus M2 protein co-purifies with cholesterol. Its proton translocation activity, responsible for virus uncoating, is not cholesterol-dependent, and the transmembrane channel appears too short for integral raft insertion. Cholesterol binding may be mediated by CRAC motifs in the flexible post-TM domain, which harbours three determinants of binding to membrane rafts. Mutation of the CRAC motif of the WSN strain attenuates virulence for mice. Its affinity to the raft-non-raft interface is predicted to target M2 protein to the periphery of lipid raft microdomains, the sites of virus assembly. Its influence on the morphology of budding virus implicates M2 as factor in virus fission at the raft boundary. Moreover, M2 is an essential factor in sorting the segmented genome into virus particles, indicating that M2 also has a role in priming the outgrowth of virus buds.SFV E1 protein is the first viral type-II fusion protein demonstrated to directly bind cholesterol when the fusion peptide loop locks into the target membrane. Cholesterol binding is modulated by another, proximal loop, which is also important during virus budding and as a host range determinant, as shown by mutational studies.
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Affiliation(s)
- Cornelia Schroeder
- Max Planck Institute for Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, D-01307, Dresden, Germany.
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33
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34
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Identification of the functional core of the influenza A virus A/M2 proton-selective ion channel. Proc Natl Acad Sci U S A 2009; 106:12283-8. [PMID: 19590009 DOI: 10.1073/pnas.0905726106] [Citation(s) in RCA: 138] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The influenza A virus M2 protein (A/M2) is a homotetrameric pH-activated proton transporter/channel that mediates acidification of the interior of endosomally encapsulated virus. This 97-residue protein has a single transmembrane (TM) helix, which associates to form homotetramers that bind the anti-influenza drug amantadine. However, the minimal fragment required for assembly and proton transport in cellular membranes has not been defined. Therefore, the conductance properties of truncation mutants expressed in Xenopus oocytes were examined. A short fragment spanning residues 21-61, M2(21-61), was inserted into the cytoplasmic membrane and had specific, amantadine-sensitive proton transport activity indistinguishable from that of full-length A/M2; an epitope-tagged version of an even shorter fragment, M2(21-51)-FLAG, had specific activity within a factor of 2 of the full-length protein. Furthermore, synthetic fragments including a peptide spanning residues 22-46 were found to transport protons into liposomes in an amantadine-sensitive manner. In addition, the functionally important His-37 residue pK(a) values are highly perturbed in the tetrameric form of the protein, a property conserved in the TM peptide and full-length A/M2 in both micelles and bilayers. These data demonstrate that the determinants for folding, drug binding, and proton translocation are packaged in a remarkably small peptide that can now be studied with confidence.
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35
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Stability and function of the influenza A virus M2 ion channel protein is determined by both extracellular and cytoplasmic domains. Arch Virol 2008; 154:147-51. [PMID: 19082683 DOI: 10.1007/s00705-008-0283-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2008] [Accepted: 11/14/2008] [Indexed: 10/21/2022]
Abstract
A series of M2/NB chimeras were used to investigate the ion channel activity of the IAV M2 protein. Replacing the M2 cytoplasmic domain with the equivalent NB domain (AAB chimera) did not influence ion channel activity, while replacement of N-terminal domains (BAA and BAB chimeras) resulted in loss of activity. Extension of the M2 protein N-terminal domain resulted in full restoration of ion channel activity in BAA chimeras but only partial restoration in BAB. While not directly involved in ion channel activity, the N- and C-terminals of M2 are important for stabilization of the transmembrane domain structure.
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36
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The influenza virus M2 protein cytoplasmic tail interacts with the M1 protein and influences virus assembly at the site of virus budding. J Virol 2008; 82:10059-70. [PMID: 18701586 DOI: 10.1128/jvi.01184-08] [Citation(s) in RCA: 188] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The cytoplasmic tail of the influenza A virus M2 proton-selective ion channel has been shown to be important for virus replication. Previous analysis of M2 cytoplasmic tail truncation mutants demonstrated a defect in incorporation of viral RNA (vRNA) into virions, suggesting a role for M2 in the recruitment of M1-vRNA complexes. To further characterize the effect of the M2 cytoplasmic tail mutations on virus assembly and budding, we constructed a series of alanine substitution mutants of M2 with mutations in the cytoplasmic tail, from residues 71 to 97. Mutant proteins M2-Mut1 and M2-Mut2, with mutations of residues 71 to 73 and 74 to 76, respectively, appeared to have the greatest effect on virus-like particle and virus budding, showing a defect in M1 incorporation. Mutant viruses containing M2-Mut1 and M2-Mut2 failed to replicate in multistep growth analyses on wild-type (wt) MDCK cells and were able to form plaques only on MDCK cells stably expressing wt M2 protein. Compared to wt M2 protein, M2-Mut1 and M2-Mut2 were unable to efficiently coimmunoprecipitate with M1. Furthermore, statistical analysis of planar sheets of membrane from cells infected by virus containing M2-Mut1 revealed a reduction in M1-hemagglutinin (HA) and M2-HA clustering as well as a severe loss of clustering between M1 and M2. These results suggest an essential, direct interaction between the cytoplasmic tail of M2 and M1 that promotes the recruitment of the internal viral proteins and vRNA to the plasma membrane for efficient virus assembly to occur.
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37
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Structural basis for the function and inhibition of an influenza virus proton channel. Nature 2008; 451:596-9. [PMID: 18235504 DOI: 10.1038/nature06528] [Citation(s) in RCA: 481] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2007] [Accepted: 12/06/2007] [Indexed: 12/15/2022]
Abstract
The M2 protein from influenza A virus is a pH-activated proton channel that mediates acidification of the interior of viral particles entrapped in endosomes. M2 is the target of the anti-influenza drugs amantadine and rimantadine; recently, resistance to these drugs in humans, birds and pigs has reached more than 90% (ref. 1). Here we describe the crystal structure of the transmembrane-spanning region of the homotetrameric protein in the presence and absence of the channel-blocking drug amantadine. pH-dependent structural changes occur near a set of conserved His and Trp residues that are involved in proton gating. The drug-binding site is lined by residues that are mutated in amantadine-resistant viruses. Binding of amantadine physically occludes the pore, and might also perturb the pK(a) of the critical His residue. The structure provides a starting point for solving the problem of resistance to M2-channel blockers.
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38
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Abstract
Matrix protein (M)2 is an Influenza A, type III membrane protein with an extracellular domain (ectodomain of M2 [M2e]) of 23 amino acid residues, which is strongly conserved across virus strains. M2 fulfills an important biological function in the life cycle of the Influenza A virus and has been a target of antiviral drugs. M2e has generated much interest as a potential vaccine target, and a clinical M2e vaccine trial was initiated in 2007. The advantage of M2e compared with hemagglutinin, the prime antigen target in conventional influenza vaccines, is that its sequence is conserved. This means that a stable, efficacious and easily produced M2e-based vaccine would provide protection not only against drifting seasonal influenza epidemic strains, but would also make it possible to vaccinate in anticipation of an emerging pandemic. Furthermore, most reported M2e-based vaccines are produced by economical and safe technologies. IgG subtype antibodies directed against M2e can prevent death from influenza and reduce morbidity in animal models for influenza disease. The immunological mechanism that mediates protection by anti-M2e antibodies is not completely understood, but it probably involves antibody-mediated cellular cytotoxicity. This review summarizes the findings on M2e vaccine candidates and addresses some of the key unanswered questions about this promising Influenza A vaccine target: what is its likely mechanism of action? Which measurable parameters correlate with protection? And what can be expected from clinical use of an M2e-based vaccine?
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Affiliation(s)
- Xavier Saelens
- Department for Molecular Biomedical Research, VIB, Ghent, Belgium, and, Department for Molecular Biology, Ghent University, Ghent Technologiepark 927, B-9052 Ghent, Belgium
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39
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Abstract
The outbreaks of avian influenza A virus in poultry and humans over the last decade posed a pandemic threat to human. Here, we discuss the basic classification and the structure of influenza A virus. The viral genome contains eight RNA viral segments and the functions of viral proteins encoded by this genome are described. In addition, the RNA transcription and replication of this virus are reviewed.
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Affiliation(s)
- Timothy K W Cheung
- Department of Microbiology, University of Hong Kong, Queen Mary Hospital, Pokfulam, Hong Kong, China
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40
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McCown MF, Pekosz A. Distinct domains of the influenza a virus M2 protein cytoplasmic tail mediate binding to the M1 protein and facilitate infectious virus production. J Virol 2006; 80:8178-89. [PMID: 16873274 PMCID: PMC1563831 DOI: 10.1128/jvi.00627-06] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The cytoplasmic tail of the influenza A virus M2 protein is highly conserved among influenza A virus isolates. The cytoplasmic tail appears to be dispensable with respect to the ion channel activity associated with the protein but important for virus morphology and the production of infectious virus particles. Using reverse genetics and transcomplementation assays, we demonstrate that the M2 protein cytoplasmic tail is a crucial mediator of infectious virus production. Truncations of the M2 cytoplasmic tail result in a drastic decrease in infectious virus titers, a reduction in the amount of packaged viral RNA, a decrease in budding events, and a reduction in budding efficiency. The M1 protein binds to the M2 cytoplasmic tail, but the M1 binding site is distinct from the sequences that affect infectious virus particle formation. Influenza A virus strains A/Udorn/72 and A/WSN/33 differ in their requirements for M2 cytoplasmic tail sequences, and this requirement maps to the M1 protein. We conclude that the M2 protein is required for the formation of infectious virus particles, implicating the protein as important for influenza A virus assembly in addition to its well-documented role during virus entry and uncoating.
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Affiliation(s)
- Matthew F McCown
- Department of Molecular Microbiology, Washington University School of Medicine, Campus Box 8230, 660 S. Euclid Ave., St. Louis, MO 63110-1093, USA
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41
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Leser GP, Lamb RA. Influenza virus assembly and budding in raft-derived microdomains: a quantitative analysis of the surface distribution of HA, NA and M2 proteins. Virology 2005; 342:215-27. [PMID: 16249012 DOI: 10.1016/j.virol.2005.09.049] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2005] [Revised: 08/02/2005] [Accepted: 09/20/2005] [Indexed: 11/24/2022]
Abstract
Influenza virus hemagglutinin (HA) and neuraminidase (NA) are known to associate with lipid rafts, membrane microdomains comprised of densely packed cholesterol and sphingolipids. These specialized membrane regions are believed to be involved in the budding of many enveloped viruses including influenza virus. Quantitative analysis of HA distribution on the surface of virus-infected cells by immunogold staining shows an organization into clusters that grow in size as the expression level of HA increases with time post-infection (p.i.) ( approximately 325-500 nm at 4 h p.i. and approximately 425-600 nm at 6 h p.i.). These HA-containing clusters are likely derived from lipid rafts as they contain a high density of the raft marker ganglioside GM1 and are dependent upon the presence of cholesterol. The clustering of HA is an intrinsic property of the HA protein and occurs in the absence of expression of other viral proteins. NA is also found sequestered within the same microdomains as HA, whereas the M2 ion channel protein does not concentrate within the raft-like microdomains. Quantification of the distribution of surface expressed HA by examining serial sections of virus-infected cells suggests that the HA-containing microdomains give rise to regions of influenza assembly and budding.
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Affiliation(s)
- George P Leser
- Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, 2205 Tech Drive, Evanston, IL 60208-3500, USA
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42
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Bourmakina SV, García-Sastre A. The morphology and composition of influenza A virus particles are not affected by low levels of M1 and M2 proteins in infected cells. J Virol 2005; 79:7926-32. [PMID: 15919950 PMCID: PMC1143655 DOI: 10.1128/jvi.79.12.7926-7932.2005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We generated a recombinant influenza A virus (Mmut) that produced low levels of matrix (M1) and M2 proteins in infected cells. Mmut virus propagated to significantly lower titers than did wild-type virus in cells infected at low multiplicity. By contrast, virion morphology and incorporation of viral proteins and vRNAs into virus particles were similar to those of wild-type virus. We propose that a threshold amount of M1 protein is needed for the assembly of viral components into an infectious particle and that budding is delayed in Mmut virus-infected cells until sufficient levels of M1 protein accumulate at the plasma membrane.
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Affiliation(s)
- Svetlana V Bourmakina
- Department of Microbiology, Mount Sinai School of Medicine, 1 Gustave L. Levy Place, Box 1124, New York, NY 10029, USA
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43
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Carrasco M, Amorim MJ, Digard P. Lipid raft-dependent targeting of the influenza A virus nucleoprotein to the apical plasma membrane. Traffic 2005; 5:979-92. [PMID: 15522099 DOI: 10.1111/j.1600-0854.2004.00237.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Influenza virus acquires a lipid raft-containing envelope by budding from the apical surface of epithelial cells. Polarised budding involves specific sorting of the viral membrane proteins, but little is known about trafficking of the internal virion components. We show that during the later stages of virus infection, influenza nucleoprotein (NP) and polymerase (the protein components of genomic ribonucleoproteins) localised to apical but not lateral or basolateral membranes, even in cell types where haemagglutinin was found on all external membranes. Other cytosolic components of the virion either distributed throughout the cytoplasm (NEP/NS2) or did not localise solely to the apical plasma membrane in all cell types (M1). NP localised specifically to the apical surface even when expressed alone, indicating intrinsic targeting. A similar proportion of NP associated with membrane fractions in flotation assays from virus-infected and plasmid-transfected cells. Detergent-resistant flotation at 4 degrees C suggested that these membranes were lipid raft microdomains. Confirming this, cholesterol depletion rendered NP detergent-soluble and furthermore, resulted in its partial redistribution throughout the cell. We conclude that NP is independently targeted to the apical plasma membrane through a mechanism involving lipid rafts and propose that this helps determine the polarity of influenza virus budding.
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Affiliation(s)
- Marlene Carrasco
- Division of Virology, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
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44
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Abstract
Rhabdoviruses are a diverse, widely-distributed group of enveloped viruses that assemble and bud from the plasma membrane of host cells. Recent advances in the identification of domains on both the envelope glycoprotein and the matrix protein of rhabdoviruses that contribute to virus assembly and release have allowed us to refine current models of rhabdovirus budding and to describe in better detail the interplay between both viral and cellular components involved in the budding process. In this review we discuss the steps involved in rhabdovirus assembly beginning with genome encapsidation and the association of nucleocapsid-matrix protein pre-assembly complexes with the inner leaflet of the plasma membrane, how condensation of these complexes may occur, how microdomains containing the envelope glycoprotein facilitate bud site formation, and how multiple forms of the matrix protein may participate in virion extrusion and release.
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Affiliation(s)
- Himangi R Jayakar
- GTx Inc., 3 N. Dunlap, Van Vleet Research Building, Memphis, TN 38163, USA
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45
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Jackson D, Zürcher T, Barclay W. Reduced incorporation of the influenza B virus BM2 protein in virus particles decreases infectivity. Virology 2004; 322:276-85. [PMID: 15110525 DOI: 10.1016/j.virol.2004.02.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2003] [Revised: 12/10/2003] [Accepted: 02/05/2004] [Indexed: 11/22/2022]
Abstract
BM2 is the fourth integral membrane protein encoded by the influenza B virus genome. It is synthesized late in infection and transported to the plasma membrane from where it is subsequently incorporated into progeny virus particles. It has recently been reported that BM2 has ion channel activity and may be the functional homologue of the influenza A virus M2 protein acting as an ion channel involved in viral entry. Using a reverse genetic approach it was not possible to recover virus which lacked BM2. A recombinant influenza B virus was generated in which the BM2 AUG initiation codon was mutated to GUG. This decreased the efficiency of translation of BM2 protein such that progeny virions contained only 1/8 the amount of BM2 seen in wild-type virus. The reduction in BM2 incorporation resulted in a reduction in infectivity although there was no concomitant decrease in the numbers of virions released from the infected cells. These data imply that the incorporation of sufficient BM2 protein into influenza B virions is required for infectivity of the virus particles.
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Affiliation(s)
- David Jackson
- School of Animal and Microbial Sciences, University of Reading, Reading, RG6 6AJ, UK
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46
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Oliveira BCEPD, Liberto MIM, Barth OM, Cabral MC. Construction of yellow fever-influenza A chimeric virus particles. J Virol Methods 2002; 106:185-96. [PMID: 12393149 DOI: 10.1016/s0166-0934(02)00164-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In order to obtain a better understanding of the functional mechanisms involved in the fusogenesis of enveloped viruses, the influenza A (X31) and the yellow fever (17DD) virus particles were used to construct a chimeric structure based on their distinct pH requirements for fusion, and the distinct malleability of their nucleocapsids. The malleable nucleocapsid of the influenza A virus particle is characterized by a pleomorphic configuration when observed by electron microscopy. A heat inactivated preparation of X31 virus was used as a lectin to interact with the sialic acid domains present in the 17DD virus envelope. The E spikes of 17DD virus were induced to promote fusion of both envelopes, creating a double genome enveloped structure, the chimeric yellow fever-influenza A virus particle. These chimeric viral particles, originally denominated 'partículas virais quiméricas' (PVQ), were characterized by their infectious capacity for different biological systems. Cell inoculation with PVQ resulted in viral products that showed similar characteristics to those obtained after 17DD virus infections. Our findings open new opportunities towards the understanding of both virus particles and aspects of cellular physiologic quality control. The yellow fever-influenza A chimeric particles, by means of their hybrid composition, should be a valuable tool in the study of cell biology and the function of viral components.
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Affiliation(s)
- B C E P D Oliveira
- Laboratório de Estruturas de Superfície de Vírus Envelopados e Interferons, Departamento de Virologia, Instituto de Microbiologia Professor Paulo de Góes, UFRJ, Caixa Postal, 68040 Rio de Janeiro, RJ, Brazil
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47
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Watanabe T, Watanabe S, Ito H, Kida H, Kawaoka Y. Influenza A virus can undergo multiple cycles of replication without M2 ion channel activity. J Virol 2001; 75:5656-62. [PMID: 11356973 PMCID: PMC114278 DOI: 10.1128/jvi.75.12.5656-5662.2001] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ion channel proteins are common constituents of cells and have even been identified in some viruses. For example, the M2 protein of influenza A virus has proton ion channel activity that is thought to play an important role in viral replication. Because direct support for this function is lacking, we attempted to generate viruses with defective M2 ion channel activity. Unexpectedly, mutants with apparent loss of M2 ion channel activity by an in vitro assay replicated as efficiently as the wild-type virus in cell culture. We also generated a chimeric mutant containing an M2 protein whose transmembrane domain was replaced with that from the hemagglutinin glycoprotein. This virus replicated reasonably well in cell culture but showed no growth in mice. Finally, a mutant lacking both the transmembrane and cytoplasmic domains of M2 protein grew poorly in cell culture and showed no growth in mice. Thus, influenza A virus can undergo multiple cycles of replication without the M2 transmembrane domain responsible for ion channel activity, although this activity promotes efficient viral replication.
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Affiliation(s)
- T Watanabe
- Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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48
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Watanabe S, Takada A, Watanabe T, Ito H, Kida H, Kawaoka Y. Functional importance of the coiled-coil of the Ebola virus glycoprotein. J Virol 2000; 74:10194-201. [PMID: 11024148 PMCID: PMC102058 DOI: 10.1128/jvi.74.21.10194-10201.2000] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ebola virus contains a single glycoprotein (GP) that is responsible for receptor binding and membrane fusion and is proteolytically cleaved into disulfide-linked GP1 and GP2 subunits. The GP2 subunit possesses a coiled-coil motif, which plays an important role in the oligomerization and fusion activity of other viral GPs. To determine the functional significance of the coiled-coil motif of GP2, we examined the effects of peptides corresponding to the coiled-coil motif of GP2 on the infectivity of a mutant vesicular stomatitis virus (lacking the receptor-binding/fusion protein) pseudotyped with the Ebola virus GP. A peptide corresponding to the C-terminal helix reduced the infectivity of the pseudotyped virus. We next introduced alanine substitutions into hydrophobic residues in the coiled-coil motif to identify residues important for GP function. None of the substitutions affected GP oligomerization, but some mutations, two in the N-terminal helix and all in the C-terminal helix, reduced the ability of GP to confer infectivity to the mutant vesicular stomatitis virus without affecting the transport of GP to the cell surface, its incorporation into virions, and the production of virus particles. These results indicate that the coiled-coil motif of GP2 plays an important role in facilitating the entry of Ebola virus into host cells and that peptides corresponding to this region could act as efficient antiviral agents.
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Affiliation(s)
- S Watanabe
- Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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49
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Robison CS, Whitt MA. The membrane-proximal stem region of vesicular stomatitis virus G protein confers efficient virus assembly. J Virol 2000; 74:2239-46. [PMID: 10666254 PMCID: PMC111705 DOI: 10.1128/jvi.74.5.2239-2246.2000] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In this report, we show that the glycoprotein of vesicular stomatitis virus (VSV G) contains within its extracellular membrane-proximal stem (GS) a domain that is required for efficient VSV budding. To determine a minimal sequence in GS that provides for high-level virus assembly, we have generated a series of recombinant DeltaG-VSVs which express chimeric glycoproteins having truncated stem sequences. The recombinant viruses having chimeras with 12 or more membrane-proximal residues of the G stem, and including the G protein transmembrane-cytoplasmic tail domains, produced near-wild-type levels of particles. In contrast, viruses encoding chimeras with shorter or no G-stem sequences produced approximately 10- to 20-fold less. This budding domain when present in chimeric glycoproteins also promoted their incorporation into the VSV envelope. We suggest that the G-stem budding domain promotes virus release by inducing membrane curvature at sites where virus budding occurs or by recruiting condensed nucleocapsids to sites on the plasma membrane which are competent for efficient virus budding.
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Affiliation(s)
- C S Robison
- Department of Microbiology and Immunology, University of Tennessee-Memphis, Memphis, Tennessee 38163, USA
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50
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Tobler K, Kelly ML, Pinto LH, Lamb RA. Effect of cytoplasmic tail truncations on the activity of the M(2) ion channel of influenza A virus. J Virol 1999; 73:9695-701. [PMID: 10559278 PMCID: PMC113015 DOI: 10.1128/jvi.73.12.9695-9701.1999] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The M(2) protein of influenza A virus forms a proton channel that is required for viral replication. The M(2) ion channel is a homotetramer and has a 24-residue N-terminal extracellular domain, a 19-residue transmembrane domain, and a 54-residue cytoplasmic tail. We show here that the N-terminal methionine residue is cleaved from the mature protein. Translational stop codons were introduced into the M(2) cDNA at residues 46, 52, 62, 72, 77, 82, 87, and 92. The deletion mutants were designated truncx, according to the amino acid position that was changed to a stop codon. We studied the role of the cytoplasmic tail by measuring the ion channel activity (the current sensitive to the M(2)-specific inhibitor amantadine) of the cytoplasmic tail truncation mutants expressed in oocytes of Xenopus laevis. When their conductance was measured over time, mutants trunc72, trunc77, and trunc92 behaved comparably to wild-type M(2) protein (a decrease of only 4% over 30 min). In contrast, conductance decreased by 28% for trunc82, 27% for trunc62, and 81% for trunc52 channels. Complete closure of the channel could be observed in some cells for trunc62 and trunc52 within 30 min. These data suggest that a role of the cytoplasmic tail region of the M(2) ion channel is to stabilize the pore against premature closure while the ectodomain is exposed to low pH.
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Affiliation(s)
- K Tobler
- Department of Biochemistry, Northwestern University, Evanston, Illinois 60208-3500, USA
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