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Yue Z, Wu J, Teng D, Wang Z, Voth GA. Activation of the influenza B M2 proton channel (BM2). BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.26.605324. [PMID: 39091734 PMCID: PMC11291123 DOI: 10.1101/2024.07.26.605324] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 08/04/2024]
Abstract
Influenza B viruses have co-circulated during most seasonal flu epidemics and can cause significant human morbidity and mortality due to their rapid mutation, emerging drug resistance, and severe impact on vulnerable populations. The influenza B M2 proton channel (BM2) plays an essential role in viral replication, but the mechanisms behind its symmetric proton conductance and the involvement of a second histidine (His27) cluster remain unclear. Here we perform the membrane-enabled continuous constant-pH molecular dynamics simulations on wildtype BM2 and a key H27A mutant to explore its pH-dependent conformational switch. Simulations capture the activation as the first histidine (His19) protonates and reveal the transition at lower pH values compared to AM2 is a result of electrostatic repulsions between His19 and pre-protonated His27. Crucially, we provide an atomic-level understanding of the symmetric proton conduction by identifying pre-activating channel hydration in the C-terminal portion. This research advances our understanding of the function of BM2 function and lays the groundwork for further chemically reactive modeling of the explicit proton transport process as well as possible anti-flu drug design efforts.
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Affiliation(s)
- Zhi Yue
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Jiangbo Wu
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Da Teng
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | | | - Gregory A. Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
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2
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Fusaro A, Zecchin B, Giussani E, Palumbo E, Agüero-García M, Bachofen C, Bálint Á, Banihashem F, Banyard AC, Beerens N, Bourg M, Briand FX, Bröjer C, Brown IH, Brugger B, Byrne AMP, Cana A, Christodoulou V, Dirbakova Z, Fagulha T, Fouchier RAM, Garza-Cuartero L, Georgiades G, Gjerset B, Grasland B, Groza O, Harder T, Henriques AM, Hjulsager CK, Ivanova E, Janeliunas Z, Krivko L, Lemon K, Liang Y, Lika A, Malik P, McMenamy MJ, Nagy A, Nurmoja I, Onita I, Pohlmann A, Revilla-Fernández S, Sánchez-Sánchez A, Savic V, Slavec B, Smietanka K, Snoeck CJ, Steensels M, Svansson V, Swieton E, Tammiranta N, Tinak M, Van Borm S, Zohari S, Adlhoch C, Baldinelli F, Terregino C, Monne I. High pathogenic avian influenza A(H5) viruses of clade 2.3.4.4b in Europe-Why trends of virus evolution are more difficult to predict. Virus Evol 2024; 10:veae027. [PMID: 38699215 PMCID: PMC11065109 DOI: 10.1093/ve/veae027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 03/01/2024] [Accepted: 03/26/2024] [Indexed: 05/05/2024] Open
Abstract
Since 2016, A(H5Nx) high pathogenic avian influenza (HPAI) virus of clade 2.3.4.4b has become one of the most serious global threats not only to wild and domestic birds, but also to public health. In recent years, important changes in the ecology, epidemiology, and evolution of this virus have been reported, with an unprecedented global diffusion and variety of affected birds and mammalian species. After the two consecutive and devastating epidemic waves in Europe in 2020-2021 and 2021-2022, with the second one recognized as one of the largest epidemics recorded so far, this clade has begun to circulate endemically in European wild bird populations. This study used the complete genomes of 1,956 European HPAI A(H5Nx) viruses to investigate the virus evolution during this varying epidemiological outline. We investigated the spatiotemporal patterns of A(H5Nx) virus diffusion to/from and within Europe during the 2020-2021 and 2021-2022 epidemic waves, providing evidence of ongoing changes in transmission dynamics and disease epidemiology. We demonstrated the high genetic diversity of the circulating viruses, which have undergone frequent reassortment events, providing for the first time a complete overview and a proposed nomenclature of the multiple genotypes circulating in Europe in 2020-2022. We described the emergence of a new genotype with gull adapted genes, which offered the virus the opportunity to occupy new ecological niches, driving the disease endemicity in the European wild bird population. The high propensity of the virus for reassortment, its jumps to a progressively wider number of host species, including mammals, and the rapid acquisition of adaptive mutations make the trend of virus evolution and spread difficult to predict in this unfailing evolving scenario.
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Affiliation(s)
- Alice Fusaro
- European Reference Laboratory (EURL) for Avian Influenza and Newcastle Disease, Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'universita 10, Legnaro, Padua 35020, Italy
| | - Bianca Zecchin
- European Reference Laboratory (EURL) for Avian Influenza and Newcastle Disease, Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'universita 10, Legnaro, Padua 35020, Italy
| | - Edoardo Giussani
- European Reference Laboratory (EURL) for Avian Influenza and Newcastle Disease, Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'universita 10, Legnaro, Padua 35020, Italy
| | - Elisa Palumbo
- European Reference Laboratory (EURL) for Avian Influenza and Newcastle Disease, Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'universita 10, Legnaro, Padua 35020, Italy
| | - Montserrat Agüero-García
- Ministry of Agriculture, Fisheries and Food, Laboratorio Central de Veterinaria (LCV), Ctra. M-106, Km 1,4 Algete, Madrid 28110, Spain
| | - Claudia Bachofen
- Federal Department of Home Affairs FDHA Institute of Virology and Immunology IVI, Sensemattstrasse 293, Mittelhäusern 3147, Switzerland
| | - Ádám Bálint
- Veterinary Diagnostic Directorate (NEBIH), Laboratory of Virology, National Food Chain Safety Office, Tábornok utca 2, Budapest 1143, Hungary
| | - Fereshteh Banihashem
- Department of Microbiology, National Veterinary Institute (SVA), Travvägen 20, Uppsala 75189, Sweden
| | - Ashley C Banyard
- WOAH/FAO international reference laboratory for Avian Influenza and Newcastle Disease, Virology Department, Animal and Plant Health Agency-Weybridge, Woodham Lane, New Haw, Addlestone KT15 3NB, United Kingdom
| | - Nancy Beerens
- Department of Virology Wageningen Bioveterinary Research, Houtribweg 39, Lelystad 8221 RA, The Netherlands
| | - Manon Bourg
- Luxembourgish Veterinary and Food Administration (ALVA), State Veterinary Laboratory, 1 Rue Louis Rech, Dudelange 3555, Luxembourg
| | - Francois-Xavier Briand
- Agence Nationale de Sécurité Sanitaire, de l’Alimentation, de l’Environnement et du Travail, Laboratoire de Ploufragan-Plouzané-Niort, Unité de Virologie, Immunologie, Parasitologie Avaires et Cunicoles, 41 Rue de Beaucemaine – BP 53, Ploufragan 22440, France
| | - Caroline Bröjer
- Department of Pathology and Wildlife Disease, National Veterinary Institute (SVA), Travvägen 20, Uppsala 75189, Sweden
| | - Ian H Brown
- WOAH/FAO international reference laboratory for Avian Influenza and Newcastle Disease, Virology Department, Animal and Plant Health Agency-Weybridge, Woodham Lane, New Haw, Addlestone KT15 3NB, United Kingdom
| | - Brigitte Brugger
- Icelandic Food and Veterinary Authority, Austurvegur 64, Selfoss 800, Iceland
| | - Alexander M P Byrne
- WOAH/FAO international reference laboratory for Avian Influenza and Newcastle Disease, Virology Department, Animal and Plant Health Agency-Weybridge, Woodham Lane, New Haw, Addlestone KT15 3NB, United Kingdom
| | - Armend Cana
- Kosovo Food and Veterinary Agency, Sector of Serology and Molecular Diagnostics, Kosovo Food and Veterinary Laboratory, Str Lidhja e Pejes, Prishtina 10000, Kosovo
| | - Vasiliki Christodoulou
- Laboratory for Animal Health Virology Section Veterinary Services (1417), 79, Athalassa Avenue Aglantzia, Nicosia 2109, Cyprus
| | - Zuzana Dirbakova
- Department of Animal Health, State Veterinary Institute, Pod Dráhami 918, Zvolen 96086, Slovakia
| | - Teresa Fagulha
- I.P. (INIAV, I.P.), Avenida da República, Instituto Nacional de Investigação Agrária e Veterinária, Quinta do Marquês, Oeiras 2780 – 157, Portugal
| | - Ron A M Fouchier
- Department of Viroscience, Erasmus MC, Dr. Molewaterplein 40, Rotterdam 3015 GD, The Netherlands
| | - Laura Garza-Cuartero
- Department of Agriculture, Food and the Marine, Central Veterinary Research Laboratory (CVRL), Backweston Campus, Stacumny Lane, Celbridge, Co. Kildare W23 X3PH, Ireland
| | - George Georgiades
- Thessaloniki Veterinary Centre (TVC), Department of Avian Diseases, 26th October Street 80, Thessaloniki 54627, Greece
| | - Britt Gjerset
- Immunology & Virology department, Norwegian Veterinary Institute, Arboretveien 57, Oslo Pb 64, N-1431 Ås, Norway
| | - Beatrice Grasland
- Agence Nationale de Sécurité Sanitaire, de l’Alimentation, de l’Environnement et du Travail, Laboratoire de Ploufragan-Plouzané-Niort, Unité de Virologie, Immunologie, Parasitologie Avaires et Cunicoles, 41 Rue de Beaucemaine – BP 53, Ploufragan 22440, France
| | - Oxana Groza
- Republican Center for Veterinary Diagnostics (NRL), 3 street Murelor, Chisinau 2051, Republic of Moldova
| | - Timm Harder
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Südufer 10, Greifswald-Insel Riems 17493, Germany
| | - Ana Margarida Henriques
- I.P. (INIAV, I.P.), Avenida da República, Instituto Nacional de Investigação Agrária e Veterinária, Quinta do Marquês, Oeiras 2780 – 157, Portugal
| | - Charlotte Kristiane Hjulsager
- Department for Virus and Microbiological Special Diagnostics, Statens Serum Institut, 5 Artillerivej, Copenhagen DK-2300, Denmark
| | - Emiliya Ivanova
- National Reference Laboratory for Avian Influenza and Newcastle Disease, National Diagnostic and Research Veterinary Medical Institute (NDRVMI), 190 Lomsko Shose Blvd., Sofia 1231, Bulgaria
| | - Zygimantas Janeliunas
- National Food and Veterinary Risk Assessment Institute (NFVRAI), Kairiukscio str. 10, Vilnius 08409, Lithuania
| | - Laura Krivko
- Institute of Food Safety, Animal Health and Environment (BIOR), Laboratory of Microbilogy and Pathology, 3 Lejupes Street, Riga 1076, Latvia
| | - Ken Lemon
- Virological Molecular Diagnostic Laboratory, Veterinary Sciences Division, Department of Virology, Agri-Food and Bioscience Institute (AFBI), Stoney Road, Belfast BT4 3SD, Northern Ireland
| | - Yuan Liang
- Department of Veterinary and Animal Sciences, University of Copenhagen, Grønnegårdsvej 15, Frederiksberg 1870, Denmark
| | - Aldin Lika
- Animal Health Department, Food Safety and Veterinary Institute, Rruga Aleksandër Moisiu 10, Tirana 1001, Albania
| | - Péter Malik
- Veterinary Diagnostic Directorate (NEBIH), Laboratory of Virology, National Food Chain Safety Office, Tábornok utca 2, Budapest 1143, Hungary
| | - Michael J McMenamy
- Virological Molecular Diagnostic Laboratory, Veterinary Sciences Division, Department of Virology, Agri-Food and Bioscience Institute (AFBI), Stoney Road, Belfast BT4 3SD, Northern Ireland
| | - Alexander Nagy
- Department of Molecular Biology, State Veterinary Institute Prague, Sídlištní 136/24, Praha 6-Lysolaje 16503, Czech Republic
| | - Imbi Nurmoja
- National Centre for Laboratory Research and Risk Assessment (LABRIS), Kreutzwaldi 30, Tartu 51006, Estonia
| | - Iuliana Onita
- Institute for Diagnosis and Animal Health (IDAH), Str. Dr. Staicovici 63, Bucharest 050557, Romania
| | - Anne Pohlmann
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Südufer 10, Greifswald-Insel Riems 17493, Germany
| | - Sandra Revilla-Fernández
- Austrian Agency for Health and Food Safety (AGES), Institute for Veterinary Disease Control, Robert Koch Gasse 17, Mödling 2340, Austria
| | - Azucena Sánchez-Sánchez
- Ministry of Agriculture, Fisheries and Food, Laboratorio Central de Veterinaria (LCV), Ctra. M-106, Km 1,4 Algete, Madrid 28110, Spain
| | - Vladimir Savic
- Croatian Veterinary Institute, Poultry Centre, Heinzelova 55, Zagreb 10000, Croatia
| | - Brigita Slavec
- University of Ljubljana – Veterinary Faculty/National Veterinary Institute, Gerbičeva 60, Ljubljana 1000, Slovenia
| | - Krzysztof Smietanka
- Department of Poultry Diseases, National Veterinary Research Institute, Al. Partyzantow 57, Puławy 24-100, Poland
| | - Chantal J Snoeck
- Luxembourg Institute of Health (LIH), Department of Infection and Immunity, 29 Rue Henri Koch, Esch-sur-Alzette 4354, Luxembourg
| | - Mieke Steensels
- Avian Virology and Immunology, Sciensano, Rue Groeselenberg 99, Ukkel 1180, Ukkel, Belgium
| | - Vilhjálmur Svansson
- Biomedical Center, Institute for Experimental Pathology, University of Iceland, Keldnavegi 3 112 Reykjavík Ssn. 650269 4549, Keldur 851, Iceland
| | - Edyta Swieton
- Department of Poultry Diseases, National Veterinary Research Institute, Al. Partyzantow 57, Puławy 24-100, Poland
| | - Niina Tammiranta
- Finnish Food Authority, Animal Health Diagnostic Unit, Veterinary Virology, Mustialankatu 3, Helsinki FI-00790, Finland
| | - Martin Tinak
- Department of Animal Health, State Veterinary Institute, Pod Dráhami 918, Zvolen 96086, Slovakia
| | - Steven Van Borm
- Avian Virology and Immunology, Sciensano, Rue Groeselenberg 99, Ukkel 1180, Ukkel, Belgium
| | - Siamak Zohari
- Department of Microbiology, National Veterinary Institute (SVA), Travvägen 20, Uppsala 75189, Sweden
| | - Cornelia Adlhoch
- European Centre for Disease Prevention and Control, Gustav III:s boulevard 40, Solna 169 73, Sweden
| | | | - Calogero Terregino
- European Reference Laboratory (EURL) for Avian Influenza and Newcastle Disease, Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'universita 10, Legnaro, Padua 35020, Italy
| | - Isabella Monne
- European Reference Laboratory (EURL) for Avian Influenza and Newcastle Disease, Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'universita 10, Legnaro, Padua 35020, Italy
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3
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Aganovic A. pH-dependent endocytosis mechanisms for influenza A and SARS-coronavirus. Front Microbiol 2023; 14:1190463. [PMID: 37234537 PMCID: PMC10206014 DOI: 10.3389/fmicb.2023.1190463] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Accepted: 04/24/2023] [Indexed: 05/28/2023] Open
Abstract
The ongoing SARS-CoV-2 pandemic and the influenza epidemics have revived the interest in understanding how these highly contagious enveloped viruses respond to alterations in the physicochemical properties of their microenvironment. By understanding the mechanisms and conditions by which viruses exploit the pH environment of the host cell during endocytosis, we can gain a better understanding of how they respond to pH-regulated anti-viral therapies but also pH-induced changes in extracellular environments. This review provides a detailed explanation of the pH-dependent viral structural changes preceding and initiating viral disassembly during endocytosis for influenza A (IAV) and SARS coronaviruses. Drawing upon extensive literature from the last few decades and latest research, I analyze and compare the circumstances in which IAV and SARS-coronavirus can undertake endocytotic pathways that are pH-dependent. While there are similarities in the pH-regulated patterns leading to fusion, the mechanisms and pH activation differ. In terms of fusion activity, the measured activation pH values for IAV, across all subtypes and species, vary between approximately 5.0 to 6.0, while SARS-coronavirus necessitates a lower pH of 6.0 or less. The main difference between the pH-dependent endocytic pathways is that the SARS-coronavirus, unlike IAV, require the presence of specific pH-sensitive enzymes (cathepsin L) during endosomal transport. Conversely, the conformational changes in the IAV virus under acidic conditions in endosomes occur due to the specific envelope glycoprotein residues and envelope protein ion channels (viroporins) getting protonated by H+ ions. Despite extensive research over several decades, comprehending the pH-triggered conformational alterations of viruses still poses a significant challenge. The precise mechanisms of protonation mechanisms of certain during endosomal transport for both viruses remain incompletely understood. In absence of evidence, further research is needed.
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4
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Lazaridis T. Molecular origins of asymmetric proton conduction in the influenza M2 channel. Biophys J 2023; 122:90-98. [PMID: 36403086 PMCID: PMC9822799 DOI: 10.1016/j.bpj.2022.11.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Revised: 11/13/2022] [Accepted: 11/17/2022] [Indexed: 11/20/2022] Open
Abstract
The M2 proton channel of influenza A is embedded into the viral envelope and allows acidification of the virion when the external pH is lowered. In contrast, no outward proton conductance is observed when the internal pH is lowered, although outward current is observed at positive voltage. Residues Trp41 and Asp44 are known to play a role in preventing pH-driven outward conductance, but the mechanism for this is unclear. We investigate this issue using classical molecular dynamics simulations with periodic proton hops. When all key His37 residues are neutral, inward proton movement is much more facile than outward movement if the His are allowed to shuttle the proton. The preference for inward movement increases further as the charge on the His37 increases. Analysis of the trajectories reveals three factors accounting for this asymmetry. First, in the outward direction, Asp44 traps the hydronium by strong electrostatic interactions. Secondly, Asp44 and Trp41 orient the hydronium with the protons pointing inward, hampering outward Grotthus hopping. As a result, the effective barrier is lower in the inward direction. Trp41 adds to the barrier by weakly H-bonding to potential H+ acceptors. Finally, for charged His, the H3O+ in the inner vestibule tends to get trapped at lipid-lined fenestrations of the cone-shaped channel. Simulations qualitatively reproduce the experimentally observed higher outward conductance of mutants. The ability of positive voltage, unlike proton gradient, to induce an outward current appears to arise from its ability to bias H3O+ and the waters around it toward more H-outward orientations.
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Affiliation(s)
- Themis Lazaridis
- Department of Chemistry, City College of New York/CUNY, New York, New York; Graduate Programs in Chemistry, Biochemistry, and Physics, The Graduate Center, City University of New York, New York, New York.
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5
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Breitinger U, Farag NS, Sticht H, Breitinger HG. Viroporins: Structure, function, and their role in the life cycle of SARS-CoV-2. Int J Biochem Cell Biol 2022; 145:106185. [PMID: 35219876 PMCID: PMC8868010 DOI: 10.1016/j.biocel.2022.106185] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 02/15/2022] [Accepted: 02/21/2022] [Indexed: 12/12/2022]
Abstract
Viroporins are indispensable for viral replication. As intracellular ion channels they disturb pH gradients of organelles and allow Ca2+ flux across ER membranes. Viroporins interact with numerous intracellular proteins and pathways and can trigger inflammatory responses. Thus, they are relevant targets in the search for antiviral drugs. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) underlies the world-wide pandemic of COVID-19, where an effective therapy is still lacking despite impressive progress in the development of vaccines and vaccination campaigns. Among the 29 proteins of SARS-CoV-2, the E- and ORF3a proteins have been identified as viroporins that contribute to the massive release of inflammatory cytokines observed in COVID-19. Here, we describe structure and function of viroporins and their role in inflammasome activation and cellular processes during the virus replication cycle. Techniques to study viroporin function are presented, with a focus on cellular and electrophysiological assays. Contributions of SARS-CoV-2 viroporins to the viral life cycle are discussed with respect to their structure, channel function, binding partners, and their role in viral infection and virus replication. Viroporin sequences of new variants of concern (α–ο) of SARS-CoV-2 are briefly reviewed as they harbour changes in E and 3a proteins that may affect their function.
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Affiliation(s)
- Ulrike Breitinger
- Department of Biochemistry, German University in Cairo, New Cairo, Egypt
| | - Noha S Farag
- Department of Microbiology and Immunology, German University in Cairo, New Cairo, Egypt
| | - Heinrich Sticht
- Division of Bioinformatics, Institute for Biochemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
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6
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Watkins LC, DeGrado WF, Voth GA. Multiscale Simulation of an Influenza A M2 Channel Mutant Reveals Key Features of Its Markedly Different Proton Transport Behavior. J Am Chem Soc 2022; 144:769-776. [PMID: 34985907 PMCID: PMC8834648 DOI: 10.1021/jacs.1c09281] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The influenza A M2 channel, a prototype for viroporins, is an acid-activated viroporin that conducts protons across the viral membrane, a critical step in the viral life cycle. Four central His37 residues control channel activation by binding subsequent protons from the viral exterior, which opens the Trp41 gate and allows proton flux to the interior. Asp44 is essential for maintaining the Trp41 gate in a closed state at high pH, resulting in asymmetric conduction. The prevalent D44N mutant disrupts this gate and opens the C-terminal end of the channel, resulting in increased conduction and a loss of this asymmetric conduction. Here, we use extensive Multiscale Reactive Molecular Dynamics (MS-RMD) and quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations with an explicit, reactive excess proton to calculate the free energy of proton transport in this M2 mutant and to study the dynamic molecular-level behavior of D44N M2. We find that this mutation significantly lowers the barrier of His37 deprotonation in the activated state and shifts the barrier for entry to the Val27 tetrad. These free energy changes are reflected in structural shifts. Additionally, we show that the increased hydration around the His37 tetrad diminishes the effect of the His37 charge on the channel's water structure, facilitating proton transport and enabling activation from the viral interior. Altogether, this work provides key insight into the fundamental characteristics of PT in WT M2 and how the D44N mutation alters this PT mechanism, and it expands understanding of the role of emergent mutations in viroporins.
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Affiliation(s)
- Laura C. Watkins
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - William F. DeGrado
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, 94158, United States
| | - Gregory A. Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States,Corresponding Author
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7
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Aledavood E, Selmi B, Estarellas C, Masetti M, Luque FJ. From Acid Activation Mechanisms of Proton Conduction to Design of Inhibitors of the M2 Proton Channel of Influenza A Virus. Front Mol Biosci 2022; 8:796229. [PMID: 35096969 PMCID: PMC8795881 DOI: 10.3389/fmolb.2021.796229] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2021] [Accepted: 12/24/2021] [Indexed: 11/26/2022] Open
Abstract
With an estimated 1 billion people affected across the globe, influenza is one of the most serious health concerns worldwide. Therapeutic treatments have encompassed a number of key functional viral proteins, mainly focused on the M2 proton channel and neuraminidase. This review highlights the efforts spent in targeting the M2 proton channel, which mediates the proton transport toward the interior of the viral particle as a preliminary step leading to the release of the fusion peptide in hemagglutinin and the fusion of the viral and endosomal membranes. Besides the structural and mechanistic aspects of the M2 proton channel, attention is paid to the challenges posed by the development of efficient small molecule inhibitors and the evolution toward novel ligands and scaffolds motivated by the emergence of resistant strains.
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Affiliation(s)
- Elnaz Aledavood
- Departament de Nutrició, Ciències de l'Alimentació i Gastronomia, Institut de Biomedicina and Institut de Química Teòrica i Computacional, University of Barcelona, Barcelona, Spain
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum – Università di Bologna, Bologna, Italy
| | - Beatrice Selmi
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum – Università di Bologna, Bologna, Italy
| | - Carolina Estarellas
- Departament de Nutrició, Ciències de l'Alimentació i Gastronomia, Institut de Biomedicina and Institut de Química Teòrica i Computacional, University of Barcelona, Barcelona, Spain
- *Correspondence: Carolina Estarellas, ; Matteo Masetti, ; F. Javier Luque,
| | - Matteo Masetti
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum – Università di Bologna, Bologna, Italy
- *Correspondence: Carolina Estarellas, ; Matteo Masetti, ; F. Javier Luque,
| | - F. Javier Luque
- Departament de Nutrició, Ciències de l'Alimentació i Gastronomia, Institut de Biomedicina and Institut de Química Teòrica i Computacional, University of Barcelona, Barcelona, Spain
- *Correspondence: Carolina Estarellas, ; Matteo Masetti, ; F. Javier Luque,
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8
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Breitinger U, Ali NKM, Sticht H, Breitinger HG. Inhibition of SARS CoV Envelope Protein by Flavonoids and Classical Viroporin Inhibitors. Front Microbiol 2021; 12:692423. [PMID: 34305855 PMCID: PMC8297954 DOI: 10.3389/fmicb.2021.692423] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Accepted: 06/14/2021] [Indexed: 11/13/2022] Open
Abstract
Severe acute respiratory syndrome coronavirus (SARS-CoV), an enveloped single-stranded positive-sense RNA virus, is a member of the genus Betacoronavirus, family Coronaviridae. The SARS-CoV envelope protein E is a small (∼8.4 kDa) channel-forming membrane protein whose sequence is highly conserved between SARS-CoV and SARS-CoV-2. As a viroporin, it is involved in various aspects of the virus life cycle including assembly, budding, envelope formation, virus release, and inflammasome activation. Here, SARS-CoV E protein was recombinantly expressed in HEK293 cells and channel activity and the effects of viroporin inhibitors studied using patch-clamp electrophysiology and a cell viability assay. We introduced a membrane-directing signal peptide to ensure transfer of recombinant E protein to the plasma membrane. E protein expression induced transmembrane currents that were blocked by various inhibitors. In an ion-reduced buffer system, currents were proton-dependent and blocked by viroporin inhibitors rimantadine and amantadine. I-V relationships of recombinant E protein were not pH-dependent in a classical buffer system with high extracellular Na+ and high intracellular K+. E-protein mediated currents were inhibited by amantadine and rimantadine, as well as 5-(N,N-hexamethylene)amiloride (HMA). We tested a total of 10 flavonoids, finding inhibitory activity of varying potency. Epigallocatechin and quercetin were most effective, with IC50 values of 1.5 ± 0.1 and 3.7 ± 0.2 nM, respectively, similar to the potency of rimantadine (IC50 = 1.7 ± 0.6 nM). Patch-clamp results were independently verified using a modified cell viability assay for viroporin inhibitors. These results contribute to the development of novel antiviral drugs that suppress virus activity and proliferation.
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Affiliation(s)
- Ulrike Breitinger
- Department of Biochemistry, German University in Cairo, New Cairo, Egypt
| | - Nourhan K M Ali
- Department of Biochemistry, German University in Cairo, New Cairo, Egypt
| | - Heinrich Sticht
- Division of Bioinformatics, Institute of Biochemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
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9
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Zhang Q, Mei X, Zhang C, Li J, Chang N, Aji D, Shi W, Bi Y, Ma Z. Novel reassortant 2.3.4.4B H5N6 highly pathogenic avian influenza viruses circulating among wild, domestic birds in Xinjiang, Northwest China. J Vet Sci 2021; 22:e43. [PMID: 34170087 PMCID: PMC8318794 DOI: 10.4142/jvs.2021.22.e43] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Revised: 04/18/2021] [Accepted: 04/28/2021] [Indexed: 12/27/2022] Open
Abstract
Background The H5 avian influenza viruses (AIVs) of clade 2.3.4.4 circulate in wild and domestic birds worldwide. In 2017, nine strains of H5N6 AIVs were isolated from aquatic poultry in Xinjiang, Northwest China. Objectives This study aimed to analyze the origin, reassortment, and mutations of the AIV isolates. Methods AIVs were isolated from oropharyngeal and cloacal swabs of poultry. Identification was accomplished by inoculating isolates into embryonated chicken eggs and performing hemagglutination tests and reverse transcription polymerase chain reaction (RT-PCR). The viral genomes were amplified with RT-PCR and then sequenced. The sequence alignment, phylogenetic, and molecular characteristic analyses were performed by using bioinformatic software. Results Nine isolates originated from the same ancestor. The viral HA gene belonged to clade 2.3.4.4B, while the NA gene had a close phylogenetic relationship with the 2.3.4.4C H5N6 highly pathogenic avian influenza viruses (HPAIVs) isolated from shoveler ducks in Ningxia in 2015. The NP gene was grouped into an independent subcluster within the 2.3.4.4B H5N8 AIVs, and the remaining six genes all had close phylogenetic relationships with the 2.3.4.4B H5N8 HPAIVs isolated from the wild birds in China, Egypt, Uganda, Cameroon, and India in 2016–2017, Multiple basic amino acid residues associated with HPAIVs were located adjacent to the cleavage site of the HA protein. The nine isolates comprised reassortant 2.3.4.4B HPAIVs originating from 2.3.4.4B H5N8 and 2.3.4.4C H5N6 viruses in wild birds. Conclusions These results suggest that the Northern Tianshan Mountain wetlands in Xinjiang may have a key role in AIVs disseminating from Central China to the Eurasian continent and East African.
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Affiliation(s)
- Qian Zhang
- Xinjiang Key Laboratory of Biological Resources and Genetic Engineering, College of Life Science and Technology, Xinjiang University, Urumqi 830046, China
| | - Xindi Mei
- Xinjiang Key Laboratory of Biological Resources and Genetic Engineering, College of Life Science and Technology, Xinjiang University, Urumqi 830046, China
| | - Cheng Zhang
- Xinjiang Key Laboratory of Biological Resources and Genetic Engineering, College of Life Science and Technology, Xinjiang University, Urumqi 830046, China.,CAS Key Laboratory of Pathogenic Microbiology and Immunology, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Disease, Institute of Microbiology, Center for Influenza Research and Early-Warning (CASCIRE), Chinese Academy of Science, Beijing 100101, China
| | - Juan Li
- Key Laboratory of Etiology and Emerging infections Disease in Shandong First Medical University, Taian 271016, China
| | - Nana Chang
- Xinjiang Key Laboratory of Biological Resources and Genetic Engineering, College of Life Science and Technology, Xinjiang University, Urumqi 830046, China
| | - Dilihuma Aji
- Xinjiang Key Laboratory of Biological Resources and Genetic Engineering, College of Life Science and Technology, Xinjiang University, Urumqi 830046, China
| | - Weifeng Shi
- Key Laboratory of Etiology and Emerging infections Disease in Shandong First Medical University, Taian 271016, China
| | - Yuhai Bi
- Xinjiang Key Laboratory of Biological Resources and Genetic Engineering, College of Life Science and Technology, Xinjiang University, Urumqi 830046, China.,CAS Key Laboratory of Pathogenic Microbiology and Immunology, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Disease, Institute of Microbiology, Center for Influenza Research and Early-Warning (CASCIRE), Chinese Academy of Science, Beijing 100101, China.
| | - Zhenghai Ma
- Xinjiang Key Laboratory of Biological Resources and Genetic Engineering, College of Life Science and Technology, Xinjiang University, Urumqi 830046, China.
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10
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Breitinger U, Farag NS, Ali NKM, Ahmed M, El-Azizi MA, Breitinger HG. Cell viability assay as a tool to study activity and inhibition of hepatitis C p7 channels. J Gen Virol 2021; 102. [PMID: 33709903 DOI: 10.1099/jgv.0.001571] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The p7 viroporin of the hepatitis C virus (HCV) forms an intracellular proton-conducting transmembrane channel in virus-infected cells, shunting the pH of intracellular compartments and thus helping virus assembly and release. This activity is essential for virus infectivity, making viroporins an attractive target for drug development. The protein sequence and drug sensitivity of p7 vary between the seven major genotypes of the hepatitis C virus, but the essential channel activity is preserved. Here, we investigated the effect of several inhibitors on recombinant HCV p7 channels corresponding to genotypes 1a-b, 2a-b, 3a and 4a using patch-clamp electrophysiology and cell-based assays. We established a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-based cell viability assay for recombinant p7 expressed in HEK293 cells to assess channel activity and its sensitivity to inhibitors. The results from the cell viability assay were consistent with control measurements using established assays of haemadsorption and intracellular pH, and agreed with data from patch-clamp electrophysiology. Hexamethylene amiloride (HMA) was the most potent inhibitor of p7 activity, but possessed cytotoxic activity at higher concentrations. Rimantadine was active against p7 of all genotypes, while amantadine activity was genotype-dependent. The alkyl-chain iminosugars NB-DNJ, NN-DNJ and NN-DGJ were tested and their activity was found to be genotype-specific. In the current study, we introduce cell viability assays as a rapid and cost-efficient technique to assess viroporin activity and identify channel inhibitors as potential novel antiviral drugs.
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Affiliation(s)
- Ulrike Breitinger
- Department of Biochemistry, German University in Cairo, New Cairo, Egypt
| | - Noha S Farag
- Department of Microbiology and Immunology, German University in Cairo, New Cairo, Egypt
| | - Nourhan K M Ali
- Department of Biochemistry, German University in Cairo, New Cairo, Egypt
| | - Marwa Ahmed
- Present address: Institute of Biochemistry and Biophysics Friedrich-Schiller-University Jena, Hans-Knöll-Str. 2, D-07745, Jena, Germany.,Department of Biochemistry, German University in Cairo, New Cairo, Egypt
| | - Mohamed A El-Azizi
- Department of Microbiology and Immunology, German University in Cairo, New Cairo, Egypt
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11
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Farag NS, Breitinger U, Breitinger HG, El Azizi MA. Viroporins and inflammasomes: A key to understand virus-induced inflammation. Int J Biochem Cell Biol 2020; 122:105738. [PMID: 32156572 PMCID: PMC7102644 DOI: 10.1016/j.biocel.2020.105738] [Citation(s) in RCA: 84] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 03/05/2020] [Accepted: 03/06/2020] [Indexed: 02/07/2023]
Abstract
The article provides a summary on cellular receptors involved in virus immunity. It summarizes key findings on viroporins, a novel class of viral proteins and their role in the virus life cycle and host cell interactions. It presents an overview of the current understanding of inflammasomes complex activation, with special focus on NLRP3. It discusses the correlation between viroporins and inflammasomes activation and aggravated inflammatory cytokines production.
Viroporins are virus encoded proteins that alter membrane permeability and can trigger subsequent cellular signals. Oligomerization of viroporin subunits results in formation of a hydrophilic pore which facilitates ion transport across host cell membranes. These viral channel proteins may be involved in different stages of the virus infection cycle. Inflammasomes are large multimolecular complexes best recognized for their ability to control activation of caspase-1, which in turn regulates the maturation of interleukin-1 β (IL-1β) and interleukin 18 (IL-18). IL-1β was originally identified as a pro-inflammatory cytokine able to induce both local and systemic inflammation and a febrile reaction in response to infection or injury. Excessive production of IL-1β is associated with autoimmune and inflammatory diseases. Microbial derivatives, bacterial pore-forming toxins, extracellular ATP and other pathogen-associated molecular patterns trigger activation of NLRP3 inflammasomes. Recent studies have reported that viroporin activity is capable of inducing inflammasome activity and production of IL-1β, where NLRP3 is shown to be regulated by fluxes of K+, H+ and Ca2+ in addition to reactive oxygen species, autophagy and endoplasmic reticulum stress. The aim of this review is to present an overview of the key findings on viroporin activity with special emphasis on their role in virus immunity and as possible activators of inflammasomes.
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Affiliation(s)
- N S Farag
- Department of Microbiology and Immunology, German University inCairo, New Cairo, Egypt.
| | - U Breitinger
- Department of Biochemistry, German University in Cairo, New Cairo, Egypt
| | - H G Breitinger
- Department of Biochemistry, German University in Cairo, New Cairo, Egypt
| | - M A El Azizi
- Department of Microbiology and Immunology, German University inCairo, New Cairo, Egypt
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12
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Mandala VS, Loftis AR, Shcherbakov AA, Pentelute BL, Hong M. Atomic structures of closed and open influenza B M2 proton channel reveal the conduction mechanism. Nat Struct Mol Biol 2020; 27:160-167. [PMID: 32015551 PMCID: PMC7641042 DOI: 10.1038/s41594-019-0371-2] [Citation(s) in RCA: 49] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2019] [Accepted: 12/30/2019] [Indexed: 12/13/2022]
Abstract
The influenza B M2 (BM2) proton channel is activated by acidic pH to mediate virus uncoating. Unlike influenza A M2 (AM2), which conducts protons with strong inward rectification, BM2 conducts protons both inward and outward. Here we report 1.4- and 1.5-Å solid-state NMR structures of the transmembrane domain of the closed and open BM2 channels in a phospholipid environment. Upon activation, the transmembrane helices increase the tilt angle by 6° and the average pore diameter enlarges by 2.1 Å. BM2 thus undergoes a scissor motion for activation, which differs from the alternating-access motion of AM2. These results indicate that asymmetric proton conduction requires a backbone hinge motion, whereas bidirectional conduction is achieved by a symmetric scissor motion. The proton-selective histidine and gating tryptophan in the open BM2 reorient on the microsecond timescale, similar to AM2, indicating that side chain dynamics are the essential driver of proton shuttling.
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Affiliation(s)
- Venkata S Mandala
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Alexander R Loftis
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | | - Bradley L Pentelute
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA.
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13
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Watkins LC, Liang R, Swanson JMJ, DeGrado WF, Voth GA. Proton-Induced Conformational and Hydration Dynamics in the Influenza A M2 Channel. J Am Chem Soc 2019; 141:11667-11676. [PMID: 31264413 DOI: 10.1021/jacs.9b05136] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The influenza A M2 protein is an acid-activated proton channel responsible for acidification of the inside of the virus, a critical step in the viral life cycle. This channel has four central histidine residues that form an acid-activated gate, binding protons from the outside until an activated state allows proton transport to the inside. While previous work has focused on proton transport through the channel, the structural and dynamic changes that accompany proton flux and enable activation have yet to be resolved. In this study, extensive Multiscale Reactive Molecular Dynamics simulations with explicit Grotthuss-shuttling hydrated excess protons are used to explore detailed molecular-level interactions that accompany proton transport in the +0, + 1, and +2 histidine charge states. The results demonstrate how the hydrated excess proton strongly influences both the protein and water hydrogen-bonding network throughout the channel, providing further insight into the channel's acid-activation mechanism and rectification behavior. We find that the excess proton dynamically, as a function of location, shifts the protein structure away from its equilibrium distributions uniquely for different pH conditions consistent with acid-activation. The proton distribution in the xy-plane is also shown to be asymmetric about the channel's main axis, which has potentially important implications for the mechanism of proton conduction and future drug design efforts.
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Affiliation(s)
- Laura C Watkins
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Ruibin Liang
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Jessica M J Swanson
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
| | - William F DeGrado
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Gregory A Voth
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
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14
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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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15
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A Dual Motif in the Hemagglutinin of H5N1 Goose/Guangdong-Like Highly Pathogenic Avian Influenza Virus Strains Is Conserved from Their Early Evolution and Increases both Membrane Fusion pH and Virulence. J Virol 2018; 92:JVI.00778-18. [PMID: 29899102 DOI: 10.1128/jvi.00778-18] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Accepted: 06/02/2018] [Indexed: 12/27/2022] Open
Abstract
Zoonotic highly pathogenic avian influenza viruses (HPAIV) have raised serious public health concerns of a novel pandemic. These strains emerge from low-pathogenic precursors by the acquisition of a polybasic hemagglutinin (HA) cleavage site, the prime virulence determinant. However, required coadaptations of the HA early in HPAIV evolution remained uncertain. To address this question, we generated several HA1/HA2 chimeras and point mutants of an H5N1 clade 2.2.2 HPAIV and an H5N1 low-pathogenic strain. Initial surveys of 3,385 HPAIV H5 HA sequences revealed frequencies of 0.5% for the single amino acids 123R and 124I but a frequency of 97.5% for the dual combination. This highly conserved dual motif is still retained in contemporary H5 HPAIV, including the novel H5NX reassortants carrying neuraminidases of different subtypes, like the H5N8 and the zoonotic H5N6 strains. Remarkably, the earliest Asian H5N1 HPAIV, the Goose/Guangdong strains from 1996/1997, carried 123R only, whereas 124I appeared later in 1997. Experimental reversion in the HPAIV HA to the two residues 123S and124T, characteristic of low-pathogenic strains, prevented virus rescue, while the single substitutions attenuated the virus in both chicken and mice considerably, accompanied by a decreased HA fusion pH. This increased pH sensitivity of H5 HPAIV enables HA-mediated membrane fusion at a higher endosomal pH. Therefore, this HA adaptation may permit infection of cells with less-acidic endosomes, e.g., within the respiratory tract, resulting in an extended organ tropism. Taken together, HA coadaptation to increased acid sensitivity promoted the early evolution of H5 Goose/Guangdong-like HPAIV strains and is still required for their zoonotic potential.IMPORTANCE Zoonotic highly pathogenic avian influenza viruses (HPAIV) have raised serious public health concerns of a novel pandemic. Their prime virulence determinant is the polybasic hemagglutinin (HA) cleavage site. However, required coadaptations in the HA (and other genes) remained uncertain. Here, we identified the dual motif 123R/124I in the HA head that increases the activation pH of HA-mediated membrane fusion, essential for virus genome release into the cytoplasm. This motif is extremely predominant in H5 HPAIV and emerged already in the earliest 1997 H5N1 HPAIV. Reversion to 123S or 124T, characteristic of low-pathogenic strains, attenuated the virus in chicken and mice, accompanied by a decreased HA activation pH. This increased pH sensitivity of H5 HPAIV extends the viral tropism to cells with less-acidic endosomes, e.g., within the respiratory tract. Therefore, early HA adaptation to increased acid sensitivity promoted the emergence of H5 Goose/Guangdong-like HPAIV strains and is required for their zoonotic potential.
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16
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Patch-Clamp Study of Hepatitis C p7 Channels Reveals Genotype-Specific Sensitivity to Inhibitors. Biophys J 2017; 110:2419-2429. [PMID: 27276260 DOI: 10.1016/j.bpj.2016.04.018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Accepted: 04/14/2016] [Indexed: 02/07/2023] Open
Abstract
Hepatitis C is a major worldwide disease and health hazard, affecting ∼3% of the world population. The p7 protein of hepatitis C virus (HCV) is an intracellular ion channel and pH regulator that is involved in the viral replication cycle. It is targeted by various classical ion channel blockers. Here, we generated p7 constructs corresponding to HCV genotypes 1a, 2a, 3a, and 4a for recombinant expression in HEK293 cells, and studied p7 channels using patch-clamp recording techniques. The pH50 values for recombinant p7 channels were between 6.0 and 6.5, as expected for proton-activated channels, and current-voltage dependence did not show any differences between genotypes. Inhibition of p7-mediated currents by amantadine, however, exhibited significant, genotype-specific variation. The IC50 values of p7-1a and p7-4a were 0.7 ± 0.1 nM and 3.2 ± 1.2 nM, whereas p7-2a and p7-3a had 50- to 1000-fold lower sensitivity, with IC50 values of 2402 ± 334 nM and 344 ± 64 nM, respectively. The IC50 values for rimantadine were low across all genotypes, ranging from 0.7 ± 0.1 nM, 1.6 ± 0.6 nM, and 3.0 ± 0.8 nM for p7-1a, p7-3a, and p7-4a, respectively, to 24 ± 4 nM for p7-2a. Results from patch-clamp recordings agreed well with cellular assays of p7 activity, namely, measurements of intracellular pH and hemadsorption assays, which confirmed the much reduced amantadine sensitivity of genotypes 2a and 3a. Thus, our results establish patch-clamp studies of recombinant viroporins as a valid analytical tool that can provide quantitative information about viroporin channel properties, complementing established techniques.
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17
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Lin CW, Mensa B, Barniol-Xicota M, DeGrado WF, Gai F. Activation pH and Gating Dynamics of Influenza A M2 Proton Channel Revealed by Single-Molecule Spectroscopy. Angew Chem Int Ed Engl 2017; 56:5283-5287. [PMID: 28374543 PMCID: PMC5543805 DOI: 10.1002/anie.201701874] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Indexed: 12/17/2022]
Abstract
Because of its importance in viral replication, the M2 proton channel of the influenza A virus has been the focus of many studies. Although we now know a great deal about the structural architecture underlying its proton conduction function, we know little about its conformational dynamics, especially those controlling the rate of this action. Herein, we employ a single-molecule fluorescence method to assess the dynamics of the inter-helical channel motion of both full-length M2 and the transmembrane domain of M2. The rate of this motion depends not only on the identity of the channel and membrane composition but also on the pH in a sigmoidal manner. For the full-length M2 channel, the rate is increased from approximately 190 μs-1 at high pH to approximately 80 μs-1 at low pH, with a transition midpoint at pH 6.1. Because the latter value is within the range reported for the conducting pKa value of the His37 tetrad, we believe that this inter-helical motion accompanies proton conduction.
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Affiliation(s)
- Chun-Wei Lin
- Ultrafast Optical Processes Laboratory, Department of Chemistry, University of Pennsylvania, Philadelphia, 231 S. 34th Street, Philadelphia, PA, 19104, USA
| | - Bruk Mensa
- Department of Pharmaceutical Chemistry, University of California San Francisco, 600 16th Street, San Francisco, CA, 94158-2517, USA
| | - Marta Barniol-Xicota
- Department of Pharmaceutical Chemistry, University of California San Francisco, 600 16th Street, San Francisco, CA, 94158-2517, USA
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of California San Francisco, 600 16th Street, San Francisco, CA, 94158-2517, USA
| | - Feng Gai
- Ultrafast Optical Processes Laboratory, Department of Chemistry, University of Pennsylvania, Philadelphia, 231 S. 34th Street, Philadelphia, PA, 19104, USA
- Department of Chemistry, University of Pennsylvania, Philadelphia, 231 S. 34th Street, Philadelphia, PA, 19104, USA
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18
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Lin CW, Mensa B, Barniol-Xicota M, DeGrado WF, Gai F. Activation pH and Gating Dynamics of Influenza A M2 Proton Channel Revealed by Single-Molecule Spectroscopy. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201701874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Chun-Wei Lin
- Ultrafast Optical Processes Laboratory; Department of Chemistry; University of Pennsylvania, Philadelphia; 231 S. 34th Street Philadelphia PA 19104 USA
| | - Bruk Mensa
- Department of Pharmaceutical Chemistry; University of California San Francisco; 600 16th Street San Francisco CA 94158-2517 USA
| | - Marta Barniol-Xicota
- Department of Pharmaceutical Chemistry; University of California San Francisco; 600 16th Street San Francisco CA 94158-2517 USA
| | - William F. DeGrado
- Department of Pharmaceutical Chemistry; University of California San Francisco; 600 16th Street San Francisco CA 94158-2517 USA
| | - Feng Gai
- Ultrafast Optical Processes Laboratory; Department of Chemistry; University of Pennsylvania, Philadelphia; 231 S. 34th Street Philadelphia PA 19104 USA
- Department of Chemistry; University of Pennsylvania, Philadelphia; 231 S. 34th Street Philadelphia PA 19104 USA
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19
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Liang R, Swanson JMJ, Madsen JJ, Hong M, DeGrado WF, Voth GA. Acid activation mechanism of the influenza A M2 proton channel. Proc Natl Acad Sci U S A 2016; 113:E6955-E6964. [PMID: 27791184 PMCID: PMC5111692 DOI: 10.1073/pnas.1615471113] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The homotetrameric influenza A M2 channel (AM2) is an acid-activated proton channel responsible for the acidification of the influenza virus interior, an important step in the viral lifecycle. Four histidine residues (His37) in the center of the channel act as a pH sensor and proton selectivity filter. Despite intense study, the pH-dependent activation mechanism of the AM2 channel has to date not been completely understood at a molecular level. Herein we have used multiscale computer simulations to characterize (with explicit proton transport free energy profiles and their associated calculated conductances) the activation mechanism of AM2. All proton transfer steps involved in proton diffusion through the channel, including the protonation/deprotonation of His37, are explicitly considered using classical, quantum, and reactive molecular dynamics methods. The asymmetry of the proton transport free energy profile under high-pH conditions qualitatively explains the rectification behavior of AM2 (i.e., why the inward proton flux is allowed when the pH is low in viral exterior and high in viral interior, but outward proton flux is prohibited when the pH gradient is reversed). Also, in agreement with electrophysiological results, our simulations indicate that the C-terminal amphipathic helix does not significantly change the proton conduction mechanism in the AM2 transmembrane domain; the four transmembrane helices flanking the channel lumen alone seem to determine the proton conduction mechanism.
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Affiliation(s)
- Ruibin Liang
- Department of Chemistry, The University of Chicago, Chicago, IL 60637
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- James Franck Institute, The University of Chicago, Chicago, IL 60637
| | - Jessica M J Swanson
- Department of Chemistry, The University of Chicago, Chicago, IL 60637
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- James Franck Institute, The University of Chicago, Chicago, IL 60637
| | - Jesper J Madsen
- Department of Chemistry, The University of Chicago, Chicago, IL 60637
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- James Franck Institute, The University of Chicago, Chicago, IL 60637
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of San Francisco, San Francisco, CA 94158
| | - Gregory A Voth
- Department of Chemistry, The University of Chicago, Chicago, IL 60637;
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- James Franck Institute, The University of Chicago, Chicago, IL 60637
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20
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Desuzinges Mandon E, Traversier A, Champagne A, Benier L, Audebert S, Balme S, Dejean E, Rosa Calatrava M, Jawhari A. Expression and purification of native and functional influenza A virus matrix 2 proton selective ion channel. Protein Expr Purif 2016; 131:42-50. [PMID: 27825980 DOI: 10.1016/j.pep.2016.11.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Revised: 10/25/2016] [Accepted: 11/02/2016] [Indexed: 12/11/2022]
Abstract
Influenza A virus displays one of the highest infection rates of all human viruses and therefore represents a severe human health threat associated with an important economical challenge. Influenza matrix protein 2 (M2) is a membrane protein of the viral envelope that forms a proton selective ion channel. Here we report the expression and native isolation of full length active M2 without mutations or fusions. The ability of the influenza virus to efficiently infect MDCK cells was used to express native M2 protein. Using a Calixarene detergents/surfactants based approach; we were able to solubilize most of M2 from the plasma membrane and purify it. The tetrameric form of native M2 was maintained during the protein preparation. Mass spectrometry shows that M2 was phosphorylated in its cytoplasmic tail (serine 64) and newly identifies an acetylation of the highly conserved Lysine 60. ELISA shows that solubilized and purified M2 was specifically recognized by M2 antibody MAB65 and was able to displace the antibody from M2 MDCK membranes. Using a bilayer voltage clamp measurement assay, we demonstrate a pH dependent proton selective ion channel activity. The addition of the M2 ion channel blocker amantadine allows a total inhibition of the channel activity, illustrating therefore the specificity of purified M2 activity. Taken together, this work shows the production and isolation of a tetrameric and functional native M2 ion channel that will pave the way to structural and functional characterization of native M2, conformational antibody development, small molecules compounds screening towards vaccine treatment.
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Affiliation(s)
| | - Aurélien Traversier
- Laboratoire de Virologie et Pathologie Humaine (VirPath), Centre International de Recherche en Infectiologie (CIRI), U1111 INSERM, UMR 5308 CNRS, ENS Lyon, Université Claude Bernard Lyon1 (UCBL1), Lyon, France
| | - Anne Champagne
- CALIXAR, 60 Avenue Rockefeller, 69008 Lyon, France; CNRS, Institut de Chimie et Biologie de Protéines, 69007 Lyon, France
| | | | - Stéphane Audebert
- Aix Marseille Univ, CNRS, INSERM, Institut Paoli-Calmettes, CRCM, Marseille Protéomique, Marseille, France
| | - Sébastien Balme
- Institut Européen des Membranes, UMR5635, Université de Montpellier CNRS ENSCM, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
| | | | - Manuel Rosa Calatrava
- Laboratoire de Virologie et Pathologie Humaine (VirPath), Centre International de Recherche en Infectiologie (CIRI), U1111 INSERM, UMR 5308 CNRS, ENS Lyon, Université Claude Bernard Lyon1 (UCBL1), Lyon, France; VirNext, Faculté de Médecine RTH Laennec, EZUS, Lyon, France
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21
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Markiewicz BN, Lemmin T, Zhang W, Ahmed IA, Jo H, Fiorin G, Troxler T, DeGrado WF, Gai F. Infrared and fluorescence assessment of the hydration status of the tryptophan gate in the influenza A M2 proton channel. Phys Chem Chem Phys 2016; 18:28939-28950. [PMID: 27725984 PMCID: PMC5157935 DOI: 10.1039/c6cp03426h] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The M2 proton channel of the influenza A virus has been the subject of extensive studies because of its critical role in viral replication. As such, we now know a great deal about its mechanism of action, especially how it selects and conducts protons in an asymmetric fashion. The conductance of this channel is tuned to conduct protons at a relatively low biologically useful rate, which allows acidification of the viral interior of a virus entrapped within an endosome, but not so great as to cause toxicity to the infected host cell prior to packaging of the virus. The dynamic, structural and chemical features that give rise to this tuning are not fully understood. Herein, we use a tryptophan (Trp) analog, 5-cyanotryptophan, and various methods, including linear and nonlinear infrared spectroscopies, static and time-resolved fluorescence techniques, and molecular dynamics simulations, to site-specifically interrogate the structure and hydration dynamics of the Trp41 gate in the transmembrane domain of the M2 proton channel. Our results suggest that the Trp41 sidechain adopts the t90 rotamer, the χ2 dihedral angle of which undergoes an increase of approximately 35° upon changing the pH from 7.4 to 5.0. Furthermore, we find that Trp41 is situated in an environment lacking bulk-like water, and somewhat surprisingly, the water density and dynamics do not show a measurable difference between the high (7.4) and low (5.0) pH states. Since previous studies have shown that upon channel opening water flows into the cavity above the histidine tetrad (His37), the present finding thus provides evidence indicating that the lack of sufficient water molecules near Trp41 needed to establish a continuous hydrogen bonding network poses an additional energetic bottleneck for proton conduction.
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Affiliation(s)
- Beatrice N Markiewicz
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
| | - Thomas Lemmin
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California 94143, USA.
| | - Wenkai Zhang
- Ultrafast Optical Processes Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Ismail A Ahmed
- Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Hyunil Jo
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California 94143, USA.
| | - Giacomo Fiorin
- Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania 19122, USA
| | - Thomas Troxler
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. and Ultrafast Optical Processes Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California 94143, USA.
| | - Feng Gai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. and Ultrafast Optical Processes Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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22
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Dudev T, Grauffel C, Lim C. Influence of the Selectivity Filter Properties on Proton Selectivity in the Influenza A M2 Channel. J Am Chem Soc 2016; 138:13038-13047. [DOI: 10.1021/jacs.6b08041] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Todor Dudev
- Faculty
of Chemistry and Pharmacy, Sofia University, Sofia 1164, Bulgaria
- Institute
of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
| | - Cédric Grauffel
- Institute
of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
| | - Carmay Lim
- Institute
of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
- Department
of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan
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23
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Wang J, Li F, Ma C. Recent progress in designing inhibitors that target the drug-resistant M2 proton channels from the influenza A viruses. Biopolymers 2016; 104:291-309. [PMID: 25663018 DOI: 10.1002/bip.22623] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Accepted: 01/24/2015] [Indexed: 12/15/2022]
Abstract
Influenza viruses are the causative agents for seasonal influenza, which results in thousands of deaths and millions of hospitalizations each year. Moreover, sporadic transmission of avian or swan influenza viruses to humans often leads to an influenza pandemic, as there is no preimmunity in the human body to fight against such novel strains. The metastable genome of the influenza viruses, coupled with the reassortment of different strains from a wide range of host origins, leads to the continuous evolution of the influenza virus diversity. Such characteristics of influenza viruses present a grand challenge in devising therapeutic strategies to combat influenza virus infection. This review summarizes recent progress in designing small molecule inhibitors that target the drug-resistant influenza A virus M2 proton channels and highlights the contribution of mechanistic studies of proton conductance to drug discovery. The lessons learned throughout the course of M2 drug discovery might provide insights for designing inhibitors that target other therapeutically important ion channels.
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Affiliation(s)
- Jun Wang
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson, AZ, 85721.,BIO5 Institute, University of Arizona, Tucson, AZ, 85721
| | - Fang Li
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson, AZ, 85721
| | - Chunlong Ma
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson, AZ, 85721
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24
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DiFrancesco ML, Hansen UP, Thiel G, Moroni A, Schroeder I. Effect of cytosolic pH on inward currents reveals structural characteristics of the proton transport cycle in the influenza A protein M2 in cell-free membrane patches of Xenopus oocytes. PLoS One 2014; 9:e107406. [PMID: 25211283 PMCID: PMC4174909 DOI: 10.1371/journal.pone.0107406] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Accepted: 08/17/2014] [Indexed: 01/01/2023] Open
Abstract
Transport activity through the mutant D44A of the M2 proton channel from influenza virus A was measured in excised inside-out macro-patches of Xenopus laevis oocytes at cytosolic pH values of 5.5, 7.5 and 8.2. The current-voltage relationships reveal some peculiarities: 1. "Transinhibition", i.e., instead of an increase of unidirectional outward current with increasing cytosolic H(+) concentration, a decrease of unidirectional inward current was found. 2. Strong inward rectification. 3. Exponential rise of current with negative potentials. In order to interpret these findings in molecular terms, different kinetic models have been tested. The transinhibition basically results from a strong binding of H(+) to a site in the pore, presumably His37. This assumption alone already provides inward rectification and exponential rise of the IV curves. However, it results in poor global fits of the IV curves, i.e., good fits were only obtained for cytosolic pH of 8.2, but not for 7.5. Assuming an additional transport step as e.g. caused by a constriction zone at Val27 resulted in a negligible improvement. In contrast, good global fits for cytosolic pH of 7.5 and 8.2 were immediately obtained with a cyclic model. A "recycling step" implies that the protein undergoes conformational changes (assigned to Trp41 and Val27) during transport which have to be reset before the next proton can be transported. The global fit failed at the low currents at pHcyt = 5.5, as expected from the interference of putative transport of other ions besides H(+). Alternatively, a regulatory effect of acidic cytosolic pH may be assumed which strongly modifies the rate constants of the transport cycle.
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Affiliation(s)
| | - Ulf-Peter Hansen
- Department of Structural Biology, University of Kiel, Kiel, Germany
| | - Gerhard Thiel
- Plant Membrane Biophysics, Technical University of Darmstadt, Darmstadt, Germany
| | - Anna Moroni
- Department of Biosciences and CNR-IBF, University of Milan, Milan, Italy
| | - Indra Schroeder
- Plant Membrane Biophysics, Technical University of Darmstadt, Darmstadt, Germany
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25
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Wei C, Pohorille A. Activation and proton transport mechanism in influenza A M2 channel. Biophys J 2014; 105:2036-45. [PMID: 24209848 DOI: 10.1016/j.bpj.2013.08.030] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Revised: 07/09/2013] [Accepted: 08/08/2013] [Indexed: 12/23/2022] Open
Abstract
Molecular dynamics trajectories 2 μs in length have been generated for the pH-activated, tetrameric M2 proton channel of the influenza A virus in all protonation states of the pH sensor located at the His(37) tetrad. All simulated structures are in very good agreement with high-resolution structures. Changes in the channel caused by progressive protonation of His(37) provide insight into the mechanism of proton transport. The channel is closed at both His(37) and Trp(41) sites in the singly and doubly protonated states, but it opens at Trp(41) upon further protonation. Anions access the charged His(37) and by doing so stabilize the protonated states of the channel. The narrow opening at the His(37) site, further blocked by anions, is inconsistent with the water-wire mechanism of proton transport. Instead, conformational interconversions of His(37) correlated with hydrogen bonding to water molecules indicate that these residues shuttle protons in high-protonation states. Hydrogen bonds between charged and uncharged histidines are rare. The valve at Val(27) remains on average quite narrow in all protonation states but fluctuates sufficiently to support water and proton transport. A proton transport mechanism in which the channel, depending on pH, opens at either the histidine or valine gate is only partially supported by the simulations.
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Affiliation(s)
- Chenyu Wei
- NASA Ames Research Center, Moffett Field, California; Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California.
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26
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Asp44 stabilizes the Trp41 gate of the M2 proton channel of influenza A virus. Structure 2013; 21:2033-41. [PMID: 24139991 DOI: 10.1016/j.str.2013.08.029] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2013] [Revised: 08/22/2013] [Accepted: 08/26/2013] [Indexed: 01/20/2023]
Abstract
Channel gating and proton conductance of the influenza A virus M2 channel result from complex pH-dependent interactions involving the pore-lining residues His37, Trp41, and Asp44. Protons diffusing from the outside of the virus protonate His37, which opens the Trp41 gate and allows one or more protons to move into the virus interior. The Trp41 gate gives rise to a strong asymmetry in the conductance, favoring rapid proton flux only when the outside is at acid pH. Here, we show that the proton currents recorded for mutants of Asp44, including D44N found in the A/FPV/Rostock/34 strain, lose this asymmetry. Moreover, NMR and MD simulations show that the mutations induce a conformational change similar to that induced by protonation of His37 at low pH, and decrease the structural stability of the hydrophobic seal associated with the Trp41 gate. Thus, Asp44 is able to determine two important properties of the M2 proton channel.
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27
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Nanda V, Cristian L, Toptygin D, Brand L, Degrado WF. Nanosecond Dynamics of InfluenzaA/M2TM and an Amantadine Resistant Mutant Probed by Time-Dependent Red Shifts of a Native Tryptophan. Chem Phys 2013; 422:10.1016/j.chemphys.2012.12.018. [PMID: 24273370 PMCID: PMC3833813 DOI: 10.1016/j.chemphys.2012.12.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Proteins involved in functions such as electron transfer or ion transport must be capable of stabilizing transient charged species on time scales ranging from picoseconds to microseconds. We study the influenza A M2 proton channel, containing a tryptophan residue that serves as an essential part of the proton conduction pathway. We induce a transition dipole in tryptophan by photoexcitation, and then probe the dielectric stabilization of its excited state. The magnitude of the stabilization over this time regime was larger than that generally found for tryptophan in membrane or protein environments. M2 achieves a water-like stabilization over a 25 nanosecond time scale, slower than that of bulk water, but sufficiently rapid to contribute to stabilization of charge as protons diffuse through the channel. These measurements should stimulate future MD studies to clarify the role of sidechain versus non-bulk water in defining the process of relaxation.
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Affiliation(s)
- Vikas Nanda
- Center for Advanced Biotechnology and Medicine, Robert Wood Johnson Medical School - UMDNJ, Piscataway, New Jersey 08854 ; Department of Biochemistry, Robert Wood Johnson Medical School - UMDNJ, Piscataway, New Jersey 08854
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28
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Dong H, Yi M, Cross TA, Zhou HX. Ab initio calculations and validation of the pH-dependent structures of the His37-Trp41 quartet, the heart of acid activation and proton conductance in the M2 protein of Influenza A virus. Chem Sci 2013; 4:2776-2787. [PMID: 23930201 PMCID: PMC3733280 DOI: 10.1039/c3sc50293g] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The M2 protein of Influenza A virus forms a homotetrameric proton channel activated by low pH. The His37-Trp41 quartet is the heart of acid activation and proton conductance, but the functional mechanism is still controversial. We carried out ab initio calculations to model the pH-dependent structures of the His37-Trp41 quartet. In our model at neutral pH, the four His37 residues are configured into a pair of dimers; in each dimer, a proton is shared between Nδ1 on one residue and Nε2 on the other, and, under the restraint of the backbone, the two imidazole rings are nearly parallel, in contrast to a perpendicular arrangement for a free imidazole-imidazolium dimer. Within each dimer the +1 charge is highly delocalized, contributing to its stabilization in a low dielectric environment. The Nδ1-H-Nε2 strong hydrogen bonds result in significantly downfield shifted Nδ1 and Nε2 chemical shifts (at 169.7 and 167.6 ppm, respectively), in good agreement with experiments. In our model at acidic pH (where the channel becomes activated), a third proton binds to an imidazole-imidazolium dimer; the imidazole rings rotate away (each by ~55°) from each other, destroying the dimer structure. The two imidazoliums are stabilized by hydrogen bonds with water molecules and a cation-π interaction with Trp41. The Raman spectra calculated for the His37-Trp41 quartet at neutral and acidic pH are in agreement with experiments. Our calculations support an activation and conductance mechanism in which a hydronium ion from the N-terminal side passes a proton to an imidazole-imidazolium dimer; when the Trp41 gate is open, relaying of a proton onto a water molecule from the C-terminal side then allows the imidazole-imidazolium dimer to reform and be ready for the next round of proton conductance.
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Affiliation(s)
- Hao Dong
- Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
| | - Myunggi Yi
- Department of Biomedical Engineering, Pukyong National University, Busan 608-737, Korea
| | - Timothy A. Cross
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, and National High Magnetic Field Laboratory, 1800 E. Paul Dirac Dr., Tallahassee, FL 32310, USA
| | - Huan-Xiang Zhou
- Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
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29
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Zhou HX, Cross TA. Modeling the membrane environment has implications for membrane protein structure and function: influenza A M2 protein. Protein Sci 2013; 22:381-94. [PMID: 23389890 DOI: 10.1002/pro.2232] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Revised: 01/29/2013] [Accepted: 01/30/2013] [Indexed: 12/13/2022]
Abstract
The M2 protein, a proton channel, from Influenza A has been structurally characterized by X-ray diffraction and by solution and solid-state NMR spectroscopy in a variety of membrane mimetic environments. These structures show substantial backbone differences even though they all present a left-handed tetrameric helical bundle for the transmembrane domain. Variations in the helix tilt influence drug binding and the chemistry of the histidine tetrad responsible for acid activation, proton selectivity and transport. Some of the major structural differences do not arise from the lack of precision, but instead can be traced to the influences of the membrane mimetic environments. The structure in lipid bilayers displays unique chemistry for the histidine tetrad, which binds two protons cooperatively to form a pair of imidazole-imidazolium dimers. The resulting interhistidine hydrogen bonds contribute to a three orders of magnitude enhancement in tetramer stability. Integration with computation has provided detailed understanding of the functional mechanism for proton selectivity, conductance and gating of this important drug target.
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Affiliation(s)
- Huan-Xiang Zhou
- Department of Physics, Florida State University, Tallahassee, Florida 32306, USA
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30
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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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31
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Avian influenza virus hemagglutinins H2, H4, H8, and H14 support a highly pathogenic phenotype. Proc Natl Acad Sci U S A 2012; 109:2579-84. [PMID: 22308331 DOI: 10.1073/pnas.1109397109] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
High-pathogenic avian influenza viruses (HPAIVs) evolve from low-pathogenic precursors specifying the HA serotypes H5 or H7 by acquisition of a polybasic HA cleavage site. As the reason for this serotype restriction has remained unclear, we aimed to distinguish between compatibility of a polybasic cleavage site with H5/H7 HA only and unique predisposition of these two serotypes for insertion mutations. To this end, we introduced a polybasic cleavage site into the HA of several low-pathogenic avian strains with serotypes H1, H2, H3, H4, H6, H8, H10, H11, H14, or H15, and rescued HA reassortants after cotransfection with the genes from either a low-pathogenic H9N2 or high-pathogenic H5N1 strain. Oculonasal inoculation with those reassortants resulted in varying pathogenicity in chicken. Recombinants containing the engineered H2, H4, H8, or H14 in the HPAIV background were lethal and exhibited i.v. pathogenicity indices of 2.79, 2.37, 2.85, and 2.61, respectively, equivalent to naturally occurring H5 or H7 HPAIV. Moreover, the H2, H4, and H8 reassortants were transmitted to some contact chickens. The H2 reassortant gained two mutations in the M2 proton channel gate region, which is affected in some HPAIVs of various origins. Taken together, in the presence of a polybasic HA cleavage site, non-H5/H7 HA can support a highly pathogenic phenotype in the appropriate viral background, indicating requirement for further adaptation. Therefore, the restriction of natural HPAIV to serotypes H5 and H7 is likely a result of their unique predisposition for acquisition of a polybasic HA cleavage site.
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32
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Zhou HX. Mechanistic insight into the h(2)o/d (2)o isotope effect in the proton transport of the influenza virus m2 protein. J Membr Biol 2011; 244:93-6. [PMID: 22041938 PMCID: PMC3237009 DOI: 10.1007/s00232-011-9402-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Accepted: 10/15/2011] [Indexed: 11/27/2022]
Abstract
The M2 proton channel is essential for the replication of the flu virus and is a known drug target. The functional mechanism of channel activation and conductance is key to both the basic biology of viral replication and the design of drugs that can withstand mutations. A quantitative model was previously developed for calculating the rate of proton transport through the M2 channel. The permeant proton was assumed to diffuse to the pore, obligatorily bind to the His37 tetrad, and then dissociate and be released to either side of the tetrad. Here the model is used to calculate the effect of a change in solvent from H(2)O to D(2)O on the rate of proton transport. The solvent substitution affects two parameters in the model: the proton diffusion constant and the pK (a) for proton binding to the His37 tetrad. When the known effects on these two parameters are included, the deuterium isotope effect calculated from the model is in quantitatively agreement with experimental results. This strict test of the theoretical model provides strong support for the hypothesis that the permeant proton obligatorily binds to and then unbinds from the His37 tetrad. This putatively essential role of the His37 tetrad in the functional mechanism of the M2 channel makes it a promising target for designing mutation-tolerant drugs.
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Affiliation(s)
- Huan-Xiang Zhou
- Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, USA.
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33
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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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34
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Mancini N, Solforosi L, Clementi N, De Marco D, Clementi M, Burioni R. A potential role for monoclonal antibodies in prophylactic and therapeutic treatment of influenza. Antiviral Res 2011; 92:15-26. [DOI: 10.1016/j.antiviral.2011.07.013] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 05/19/2011] [Accepted: 07/12/2011] [Indexed: 10/17/2022]
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35
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Zhou HX. A theory for the proton transport of the influenza virus M2 protein: extensive test against conductance data. Biophys J 2011; 100:912-21. [PMID: 21320435 DOI: 10.1016/j.bpj.2011.01.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 12/22/2010] [Accepted: 01/04/2011] [Indexed: 11/28/2022] Open
Abstract
A theory for calculating the proton flux through the influenza virus M2 channel is tested here against an extensive set of conductance data. The flux is determined by the rate constants for binding to the His(37) tetrad from the two sides of the membrane and the corresponding unbinding rate constants. The rate constants are calculated by explicitly treating the structure and dynamics of the protein. Important features revealed by previous studies, such as a gating role for Val(27) at the entrance to the channel pore, and channel activation by viral exterior pH, are incorporated in this theory. This study demonstrates that the conductance function of the M2 proton channel can now be quantitatively rationalized by the structure and dynamics of the protein.
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Affiliation(s)
- Huan-Xiang Zhou
- Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, USA.
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36
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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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37
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Peterson E, Ryser T, Funk S, Inouye D, Sharma M, Qin H, Cross TA, Busath DD. Functional reconstitution of influenza A M2(22-62). BIOCHIMICA ET BIOPHYSICA ACTA 2011; 1808:516-21. [PMID: 20969830 PMCID: PMC3005097 DOI: 10.1016/j.bbamem.2010.10.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2010] [Revised: 10/08/2010] [Accepted: 10/14/2010] [Indexed: 01/17/2023]
Abstract
Amantadine-sensitive proton uptake by liposomes is currently the preferred method of demonstrating M2 functionality after reconstitution, to validate structural determination with techniques such as solid-state NMR. With strong driving forces (two decades each of both [K(+)] gradient-induced membrane potential and [H(+)] gradient), M2(22-62) showed a transport rate of 78 H(+)/tetramer-s (pH(o) 6.0, pH(i) 8.0, nominal V(m)=-114 mV), higher than previously measured for similar, shorter, and full-length constructs. Amantadine sensitivity of the conductance domain at pH 6.8 was also comparable to other published reports. Proton flux rate was optimal at protein densities of 0.05-1.0% (peptide wt.% in lipid). Rundown of total proton uptake after addition of valinomycin and CCCP, as detected by delayed addition of valinomycin, indicated M2-induced K(+) flux of 0.1K(+)/tetramer-s, and also demonstrated that the K(+) permeability, relative to H(+), was 2.8 × 10(-6). Transport rate, amantadine and cyclooctylamine sensitivity, acid activation, and H(+) selectivity were all consistent with full functionality of the reconstituted conductance domain. Decreased external pH increased proton uptake with an apparent pK(a) of 6.
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Affiliation(s)
- Emily Peterson
- Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602 USA.
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38
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Resistance characteristics of influenza to amino-adamantyls. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:547-53. [DOI: 10.1016/j.bbamem.2010.06.018] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Revised: 06/14/2010] [Accepted: 06/18/2010] [Indexed: 12/17/2022]
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39
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Polishchuk AL, Lear JD, Ma C, Lamb RA, Pinto LH, Degrado WF. A pH-dependent conformational ensemble mediates proton transport through the influenza A/M2 protein. Biochemistry 2010; 49:10061-71. [PMID: 20968306 DOI: 10.1021/bi101229m] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The influenza A/M2 protein exhibits inwardly rectifying, pH-activated proton transport that saturates at low pH. A comparison of high-resolution structures of the transmembrane domain at high and low pH suggests that pH-dependent conformational changes may facilitate proton conduction by alternately changing the accessibility of the N-terminal and C-terminal regions of the channel as a proton transits through the transmembrane domain. Here, we show that M2 functionally reconstituted in liposomes populates at least three different conformational states over a physiologically relevant pH range, with transition midpoints that are consistent with previously reported His37 pK(a) values. We then develop and test two similar, quantitative mechanistic models of proton transport, where protonation shifts the equilibrium between structural states having different proton affinities and solvent accessibilities. The models account well for a collection of experimental data sets over a wide range of pH values and voltages and require only a small number of adjustable parameters to accurately describe the data. While the kinetic models do not require any specific conformation for the protein, they nevertheless are consistent with a large body of structural information based on high-resolution nuclear magnetic resonance and crystallographic structures, optical spectroscopy, and molecular dynamics calculations.
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Affiliation(s)
- Alexei L Polishchuk
- Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6059, United States
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40
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Sharma M, Yi M, Dong H, Qin H, Peterson E, Busath DD, Zhou HX, Cross TA. Insight into the mechanism of the influenza A proton channel from a structure in a lipid bilayer. Science 2010; 330:509-12. [PMID: 20966252 PMCID: PMC3384994 DOI: 10.1126/science.1191750] [Citation(s) in RCA: 369] [Impact Index Per Article: 26.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The M2 protein from the influenza A virus, an acid-activated proton-selective channel, has been the subject of numerous conductance, structural, and computational studies. However, little is known at the atomic level about the heart of the functional mechanism for this tetrameric protein, a His(37)-Trp(41) cluster. We report the structure of the M2 conductance domain (residues 22 to 62) in a lipid bilayer, which displays the defining features of the native protein that have not been attainable from structures solubilized by detergents. We propose that the tetrameric His(37)-Trp(41) cluster guides protons through the channel by forming and breaking hydrogen bonds between adjacent pairs of histidines and through specific interactions of the histidines with the tryptophan gate. This mechanism explains the main observations on M2 proton conductance.
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Affiliation(s)
- Mukesh Sharma
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Myunggi Yi
- Department of Physics, Florida State University, Tallahassee, FL 32306, USA
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
| | - Hao Dong
- Department of Physics, Florida State University, Tallahassee, FL 32306, USA
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
| | - Huajun Qin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA
| | - Emily Peterson
- Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA
| | - David D. Busath
- Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA
| | - Huan-Xiang Zhou
- Department of Physics, Florida State University, Tallahassee, FL 32306, USA
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
| | - Timothy A. Cross
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
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41
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Proton and cation transport activity of the M2 proton channel from influenza A virus. Proc Natl Acad Sci U S A 2010; 107:15409-14. [PMID: 20713739 DOI: 10.1073/pnas.1009997107] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The M2 protein is a small, single-span transmembrane (TM) protein from the influenza A virus. This virus enters cells via endosomes; as the endosomes mature and become more acidic M2 facilitates proton transport into the viral interior, thereby disrupting matrix protein/RNA interactions required for infectivity. A mystery has been how protons can accumulate in the viral interior without developing a large electrical potential that impedes further inward proton translocation. Progress in addressing this question has been limited by the availability of robust methods of unidirectional insertion of the protein into virus-like vesicles. Using an optimized procedure for reconstitution, we show that M2 has antiporter-like activity, facilitating K(+) or Na(+) efflux when protons flow down a concentration gradient into the vesicles. Cation efflux is very small except under conditions mimicking those encountered by the endosomally entrapped virus, in which protons are flowing through the channel. This proton/cation exchange function is consistent with the known high proton selectivity of the channel. Thus, M2 acts as a proton uniporter that occasionally allows K(+) to flow to maintain electrical neutrality. Remarkably, as the pH inside M2-containing vesicles (pH(in)) decreases, the proton channel activity of M2 is inhibited, but its cation transport activity is activated. This reciprocal inhibition of proton flux and activation of cation flux with decreasing pH(in) first allows accumulation of protons in the early stages of acidification, then trapping of protons within the virus when low pH(in) is achieved.
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42
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Inayat S, Zhao Y, Cantrell DR, Dikin D, Pinto LH, Troy JB. A novel way to go whole-cell in patch-clamp experiments. IEEE Trans Biomed Eng 2010; 57. [PMID: 20595080 DOI: 10.1109/tbme.2010.2055055] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
With a conventional patch-clamp electrode, an Ag/AgCl wire sits stationary inside the pipette. To move from the gigaseal cell-attached configuration to whole-cell recording, suction is applied inside the pipette. We have designed and developed a novel Pushpen patch-clamp electrode, in which a W wire insulated and wound with Ag/AgCl wire can move linearly inside the pipette. The W wire has a conical tip, which can protrude from the pipette tip like a push pen, a procedure we call the Pushpen Operation. We use the Pushpen operation to impale the cell membrane in cell-attached configuration to go whole-cell without disruption of the gigaseal. We successfully recorded whole-cell currents from chinese hamster ovarian cells expressing influenza A virus protein A/M2, after obtaining whole-cell configuration with the Pushpen operation. This novel method of achieving whole-cell configuration may have a higher success rate than is the case with the conventional patch clamp technique.
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43
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Zhou HX. Diffusion-Influenced Transport of Ions across a Transmembrane Channel with an Internal Binding Site. J Phys Chem Lett 2010; 1:1973-1976. [PMID: 20625440 PMCID: PMC2897077 DOI: 10.1021/jz100683t] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We develop a microscopic theory for ion transport across a transmembrane channel with an internal binding site. The ion flux is determined by the rate constants for binding to the internal site from the two sides of the membrane and the corresponding unbinding rate constants. The binding rate constants are formulated in terms of diffusion-influenced reactions. The theory allows a reconciliation of experimental data on the conductance of the influenza A M2 proton channel with the structure and dynamics of the protein.
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Affiliation(s)
- Huan-Xiang Zhou
- Correspondence information: phone, (850) 645-1336; fax, (850) 644-7244;
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44
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Khurana E, Devane RH, Dal Peraro M, Klein ML. Computational study of drug binding to the membrane-bound tetrameric M2 peptide bundle from influenza A virus. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:530-7. [PMID: 20385097 DOI: 10.1016/j.bbamem.2010.03.025] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2010] [Revised: 03/28/2010] [Accepted: 03/31/2010] [Indexed: 12/19/2022]
Abstract
The M2 protein of influenza A virus performs the crucial function of transporting protons to the interior of virions enclosed in the endosome. Adamantane drugs, amantadine (AMN) and rimantidine (RMN), block the proton conduction in some strains, and have been used for the treatment and prophylaxis of influenza A infections. The structures of the transmembrane (TM) region of M2 that have been solved in micelles using NMR (residues 23-60) (Schnell and Chou, 2008) and by X-ray crystallography (residues 22-46) (Stouffer et al., 2008) suggest different drug binding sites: external and internal for RMN and AMN, respectively. We have used molecular dynamics (MD) simulations to investigate the nature of the binding site and binding mode of adamantane drugs on the membrane-bound tetrameric M2-TM peptide bundles using as initial conformations the low-pH AMN-bound crystal structure, a high-pH model derived from the drug-free crystal structure, and the high-pH NMR structure. The MD simulations indicate that under both low- and high-pH conditions, AMN is stable inside the tetrameric bundle, spanning the region between residues Val27 to Gly34. At low pH the polar group of AMN is oriented toward the His37 gate, while under high-pH conditions its orientation exhibits large fluctuations. The present MD simulations also suggest that AMN and RMN molecules do not show strong affinity to the external binding sites.
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Affiliation(s)
- Ekta Khurana
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
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45
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Balannik V, Carnevale V, Fiorin G, Levine BG, Lamb RA, Klein ML, Degrado WF, Pinto LH. Functional studies and modeling of pore-lining residue mutants of the influenza a virus M2 ion channel. Biochemistry 2010; 49:696-708. [PMID: 20028125 DOI: 10.1021/bi901799k] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The A/M2 protein of influenza A virus forms a tetrameric proton-selective pH-gated ion channel. The H(37)xxxW(41) motif located in the channel pore is responsible for its gating and proton selectivity. Channel activation most likely involves protonation of the H37 residues, while the conductive state of the channel is characterized by two or three charged His residues in a tetrad. A/M2 channel activity is inhibited by the antiviral drug amantadine. Although a large number of functional amantadine-resistant mutants of A/M2 have been observed in vitro, only a few are observed in highly transmissible viruses in the presence or absence of amantadine. We therefore examined 49 point mutants of the pore-lining residues, representing both natural and nonnatural variants. Their ion selectivity, amantadine sensitivity, specific activity, and pH-dependent conductance were measured in Xenopus oocytes. These measurements showed how variations in the sequence lead to variations in the proton conduction. The results are consistent with a multistep mechanism that allows the protein to fine-tune its pH-rate profile over a wide range of proton concentrations, hypothesized to arise from different protonation states of the H37 tetrad. Mutations that give native-like conductance at low pH as well as minimal leakage current at pH 7.0 were surprisingly rare. Moreover, the results are consistent with a location of the amantadine-binding site inside the channel pore. These findings have helped to define the set of functionally fit mutants that should be targeted when considering the design of novel drugs that inhibit amantadine-resistant strains of influenza A virus.
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Affiliation(s)
- Victoria Balannik
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208-3500, USA
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46
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Mustafa M, Henderson DJ, Busath DD. Free-energy profiles for ions in the influenza M2-TMD channel. Proteins 2009; 76:794-807. [PMID: 19296508 DOI: 10.1002/prot.22376] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
M(2) transmembrane domain channel (M(2)-TMD) permeation properties are studied using molecular dynamics simulations of M(2)-TMD (1NYJ) embedded in a lipid bilayer (DMPC) with 1 mol/kg NaCl or KCl saline solution. This study allows examination of spontaneous cation and anion entry into the selectivity filter. Three titration states of the M(2)-TMD tetramer are modeled for which the four His(37) residues, forming the selectivity filter, are net uncharged, +2 charged, or +3 charged. M(2)-TMD structural properties from our simulations are compared with the properties of other models extracted from NMR and X-ray studies. During 10 ns simulations, chloride ions occasionally occupy the positively-charged selectivity filter region, and from umbrella sampling simulations, Cl(-) has a lower free-energy barrier in the selectivity-filter region than either Na(+) or NH(4) (+), and NH(4) (+) has a lower free-energy barrier than Na(+). For Na(+) and Cl(-), the free-energy barriers are less than 5 kcal/mol, suggesting that the 1NYJ conformation would probably not be exquisitely proton selective. We also point out a rotameric configuration of Trp(41) that could fully occlude the channel.
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Affiliation(s)
- Morad Mustafa
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, USA.
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47
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Comparison of the activities of BM2 protein and its H19 and W23 mutants of influenza B virus with activities of M2 protein and its H37 and W41 mutants of influenza A virus. Arch Virol 2009; 154:1619-24. [PMID: 19763781 DOI: 10.1007/s00705-009-0483-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2009] [Accepted: 07/24/2009] [Indexed: 10/20/2022]
Abstract
Co-expression of the BM2 protein with pH-sensitive HA reduces the conversion of HA to its low-pH conformation during transport to the cell surface in the same way as human M2 proteins. BM2 protein is capable of increasing vesicular pH by as much as 0.4 pH units. Mutation analysis showed that replacement of H19 in BM2 protein by A and L resulted in loss of activity, while M2, with the mutation H37A, remained active, but its severe toxicity was intolerable for cells. Whereas substitution of L or A for W23 abolished detectable activity of the BM2 channel, substitution of L for W41 in the M2 protein resulted in a functional ion channel but with reduced activity. W41 was not essential for functional activity of the M2 protein. Our results show some differences in the nature of the interaction of the histidine and tryptophan in the transmembrane domains of BM2 and M2 ion channels.
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48
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Conformational heterogeneity of the M2 proton channel and a structural model for channel activation. Proc Natl Acad Sci U S A 2009; 106:13311-6. [PMID: 19633188 DOI: 10.1073/pnas.0906553106] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The M2 protein of influenza virus A is a proton-selective ion channel activated by pH. Structure determination by solid-state and solution NMR and X-ray crystallography has contributed significantly to our understanding, but channel activation may involve conformations not captured by these studies. Indeed, solid-state NMR data demonstrate that the M2 protein possesses significant conformational heterogeneity. Here, we report molecular dynamics (MD) simulations of the M2 transmembrane domain (TMD) in the absence and presence of the antiviral drug amantadine. The ensembles of MD conformations for both apo and bound forms reproduced the NMR data well. The TMD helix was found to kink around Gly-34, where water molecules penetrated deeply into the backbone. The amantadine-bound form exhibited a single peak approximately 10 degrees in the distribution of helix-kink angle, but the apo form exhibited 2 peaks, approximately 0 degrees and 40 degrees . Conformations of the apo form with small and large kink angles had narrow and wide pores, respectively, around the primary gate formed by His-37 and Trp-41. We propose a structural model for channel activation, in which the small-kink conformations dominate before proton uptake by His-37 from the exterior, and proton uptake makes the large-kink conformations more favorable, thereby priming His-37 for proton release to the interior.
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49
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Mechanism of drug inhibition and drug resistance of influenza A M2 channel. Proc Natl Acad Sci U S A 2009; 106:7379-84. [PMID: 19383794 DOI: 10.1073/pnas.0902548106] [Citation(s) in RCA: 220] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The influenza A virus M2 proton channel equilibrates pH across the viral membrane during entry and across the trans-Golgi membrane of infected cells during viral maturation. It is an important target of adamantane-family antiviral drugs, but drug resistance has become a critical problem. Two different sites for drug interaction have been proposed. One is a lipid-facing pocket between 2 adjacent transmembrane helices (around Asp-44), at which the drug binds and inhibits proton conductance allosterically. The other is inside the pore (around Ser-31), at which the drug directly blocks proton passage. Here, we describe structural and functional experiments on the mechanism of drug inhibition and resistance. The solution structure of the S31N drug-resistant mutant of M2, a mutant of the highly pathogenic avian influenza subtype H5N1, shows that replacing Ser-31 with Asn has little effect on the structure of the channel pore, but dramatically reduces drug binding to the allosteric site. Mutagenesis and liposomal proton flux assays show that replacing the key residue (Asp-44) in the lipid-facing binding pocket with Ala has a dramatic effect on drug sensitivity, but that the channel remains fully drug sensitive when replacing Ser-31 with Ala. Chemical cross-linking studies indicate an inverse correlation between channel stability and drug resistance. The lipid-facing pocket contains residues from 2 adjacent channel-forming helices. Therefore, it is present only when the helices are tightly packed in the closed conformation. Thus, drug-resistant mutants impair drug binding by destabilizing helix-helix assembly.
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50
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Molecular dynamics calculations suggest a conduction mechanism for the M2 proton channel from influenza A virus. Proc Natl Acad Sci U S A 2009; 106:1069-74. [PMID: 19144924 DOI: 10.1073/pnas.0811720106] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The M2 protein of the influenza A virus is activated by low endosomal pH and performs the essential function of proton transfer into the viral interior. The resulting decrease in pH within the virion is essential for the uncoating and further replication of the viral genetic material. The x-ray crystal [Stouffer AL, et al. (2008) Nature 451:596-599] and solution NMR [Schnell JR, Chou JJ (2008) Nature 451:591-595] structures of the transmembrane region of the M2 homo-tetrameric bundle both revealed pores with narrow constrictions at one end, leaving a question as to how protons enter the channel. His-37, which is essential for proton-gating and selective conduction of protons, lies in the pore of the crystallographic and NMR structures. Here, we explore the different protonation states of the His-37 residues of the M2 bundle in a bilayer using molecular dynamics (MD) simulations. When the His-37 residues are neutral, the protein prefers an Open(out)-Closed(in) conformation in which the channel is open to the environment on the outside of the virus but closed to the interior environment of the virus. Diffusion of protons into the channel from the outside of the virus and protonation of His-37 residues in the tetramer stabilizes an oppositely gated Closed(out)-Open(in) conformation. Thus, protons might be conducted through a transporter-like mechanism, in which the protein alternates between Open(out)-Closed(in) and Closed(out)-Open(in) conformations, and His-37 is protonated/deprotonated during each turnover. The transporter-like mechanism is consistent with the known properties of the M2 bundle, including its relatively low rate of proton flux and its strong rectifying behavior.
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