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David SC, Vadas O, Glas I, Schaub A, Luo B, D'angelo G, Montoya JP, Bluvshtein N, Hugentobler W, Klein LK, Motos G, Pohl M, Violaki K, Nenes A, Krieger UK, Stertz S, Peter T, Kohn T. Inactivation mechanisms of influenza A virus under pH conditions encountered in aerosol particles as revealed by whole-virus HDX-MS. mSphere 2023; 8:e0022623. [PMID: 37594288 PMCID: PMC10597348 DOI: 10.1128/msphere.00226-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Accepted: 06/23/2023] [Indexed: 08/19/2023] Open
Abstract
Multiple respiratory viruses, including influenza A virus (IAV), can be transmitted via expiratory aerosol particles, and aerosol pH was recently identified as a major factor influencing airborne virus infectivity. Indoors, small exhaled aerosols undergo rapid acidification to pH ~4. IAV is known to be sensitive to mildly acidic conditions encountered within host endosomes; however, it is unknown whether the same mechanisms could mediate viral inactivation within the more acidic aerosol micro-environment. Here, we identified that transient exposure to pH 4 caused IAV inactivation by a two-stage process, with an initial sharp decline in infectious titers mainly attributed to premature attainment of the post-fusion conformation of viral protein haemagglutinin (HA). Protein changes were observed by hydrogen-deuterium exchange coupled to mass spectrometry (HDX-MS) as early as 10 s post-exposure to acidic conditions. Our HDX-MS data are in agreement with other more labor-intensive structural analysis techniques, such as X-ray crystallography, highlighting the ease and usefulness of whole-virus HDX-MS for multiplexed protein analyses, even within enveloped viruses such as IAV. Additionally, virion integrity was partially but irreversibly affected by acidic conditions, with a progressive unfolding of the internal matrix protein 1 (M1) that aligned with a more gradual decline in viral infectivity with time. In contrast, no acid-mediated changes to the genome or lipid envelope were detected. Improved understanding of respiratory virus fate within exhaled aerosols constitutes a global public health priority, and information gained here could aid the development of novel strategies to control the airborne persistence of seasonal and/or pandemic influenza in the future. IMPORTANCE It is well established that COVID-19, influenza, and many other respiratory diseases can be transmitted by the inhalation of aerosolized viruses. Many studies have shown that the survival time of these airborne viruses is limited, but it remains an open question as to what drives their infectivity loss. Here, we address this question for influenza A virus by investigating structural protein changes incurred by the virus under conditions relevant to respiratory aerosol particles. From prior work, we know that expelled aerosols can become highly acidic due to equilibration with indoor room air, and our results indicate that two viral proteins are affected by these acidic conditions at multiple sites, leading to virus inactivation. Our findings suggest that the development of air treatments to quicken the speed of aerosol acidification would be a major strategy to control infectious bioburdens in the air.
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Affiliation(s)
- Shannon C. David
- Environmental Chemistry Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Oscar Vadas
- Protein Platform, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Irina Glas
- Institute of Medical Virology, University of Zurich, Zürich, Switzerland
| | - Aline Schaub
- Environmental Chemistry Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Beiping Luo
- Institute for Atmospheric and Climate Science, ETH Zurich, Zürich, Switzerland
| | - Giovanni D'angelo
- Laboratory of Lipid Cell Biology, School of Life Sciences, Interschool Institute of Bioengineering and Global Health Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Jonathan Paz Montoya
- Laboratory of Lipid Cell Biology, School of Life Sciences, Interschool Institute of Bioengineering and Global Health Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Nir Bluvshtein
- Institute for Atmospheric and Climate Science, ETH Zurich, Zürich, Switzerland
| | - Walter Hugentobler
- Laboratory of Atmospheric Processes and their Impacts, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Liviana K. Klein
- Institute for Atmospheric and Climate Science, ETH Zurich, Zürich, Switzerland
| | - Ghislain Motos
- Laboratory of Atmospheric Processes and their Impacts, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Marie Pohl
- Institute of Medical Virology, University of Zurich, Zürich, Switzerland
| | - Kalliopi Violaki
- Laboratory of Atmospheric Processes and their Impacts, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Athanasios Nenes
- Laboratory of Atmospheric Processes and their Impacts, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
- Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, Greece
| | - Ulrich K. Krieger
- Institute for Atmospheric and Climate Science, ETH Zurich, Zürich, Switzerland
| | - Silke Stertz
- Institute of Medical Virology, University of Zurich, Zürich, Switzerland
| | - Thomas Peter
- Institute for Atmospheric and Climate Science, ETH Zurich, Zürich, Switzerland
| | - Tamar Kohn
- Environmental Chemistry Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
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2
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Garcia NK, Kephart SM, Benhaim MA, Matsui T, Mileant A, Guttman M, Lee KK. Structural dynamics reveal subtype-specific activation and inhibition of influenza virus hemagglutinin. J Biol Chem 2023; 299:104765. [PMID: 37121546 PMCID: PMC10220487 DOI: 10.1016/j.jbc.2023.104765] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Revised: 03/25/2023] [Accepted: 04/24/2023] [Indexed: 05/02/2023] Open
Abstract
Influenza hemagglutinin (HA) is a prototypical class 1 viral entry glycoprotein, responsible for mediating receptor binding and membrane fusion. Structures of its prefusion and postfusion forms, embodying the beginning and endpoints of the fusion pathway, have been extensively characterized. Studies probing HA dynamics during fusion have begun to identify intermediate states along the pathway, enhancing our understanding of how HA becomes activated and traverses its conformational pathway to complete fusion. HA is also the most variable, rapidly evolving part of influenza virus, and it is not known whether mechanisms of its activation and fusion are conserved across divergent viral subtypes. Here, we apply hydrogen-deuterium exchange mass spectrometry to compare fusion activation in two subtypes of HA, H1 and H3. Our data reveal subtype-specific behavior in the regions of HA that undergo structural rearrangement during fusion, including the fusion peptide and HA1/HA2 interface. In the presence of an antibody that inhibits the conformational change (FI6v3), we observe that acid-induced dynamic changes near the epitope are dampened, but the degree of protection at the fusion peptide is different for the two subtypes investigated. These results thus provide new insights into variation in the mechanisms of influenza HA's dynamic activation and its inhibition.
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Affiliation(s)
- Natalie K Garcia
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington, USA
| | - Sally M Kephart
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington, USA
| | - Mark A Benhaim
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington, USA
| | - Tsutomu Matsui
- Stanford Synchrotron Radiation Laboratory, SLAC, Menlo Park, California, USA
| | - Alexander Mileant
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington, USA
| | - Miklos Guttman
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington, USA
| | - Kelly K Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, Washington, USA.
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3
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Winter SL, Chlanda P. The Art of Viral Membrane Fusion and Penetration. Subcell Biochem 2023; 106:113-152. [PMID: 38159225 DOI: 10.1007/978-3-031-40086-5_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2024]
Abstract
As obligate pathogens, viruses have developed diverse mechanisms to deliver their genome across host cell membranes to sites of virus replication. While enveloped viruses utilize viral fusion proteins to accomplish fusion of their envelope with the cellular membrane, non-enveloped viruses rely on machinery that causes local membrane ruptures and creates an opening through which the capsid or viral genome is released. Both membrane fusion and membrane penetration take place at the plasma membrane or in intracellular compartments, often involving the engagement of the cellular machinery and antagonism of host restriction factors. Enveloped and non-enveloped viruses have evolved intricate mechanisms to enable virus uncoating and modulation of membrane fusion in a spatiotemporally controlled manner. This chapter summarizes and discusses the current state of understanding of the mechanisms of viral membrane fusion and penetration. The focus is on the role of lipids, viral scaffold uncoating, viral membrane fusion inhibitors, and host restriction factors as physicochemical modulators. In addition, recent advances in visualizing and detecting viral membrane fusion and penetration using cryo-electron microscopy methods are presented.
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Affiliation(s)
- Sophie L Winter
- Schaller Research Group, Department of Infectious Diseases, Virology, Heidelberg University Hospital, Heidelberg, Germany
| | - Petr Chlanda
- Schaller Research Group, Department of Infectious Diseases, Virology, Heidelberg University Hospital, Heidelberg, Germany.
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4
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Abstract
Serine incorporator 5 (Ser5), a transmembrane protein, has recently been identified as a host antiviral factor against human immunodeficiency virus (HIV)-1 and gammaretroviruses like murine leukemia viruses (MLVs). It is counteracted by HIV-1 Nef and MLV glycogag. We have investigated whether it has antiviral activity against influenza A virus (IAV), as well as retroviruses. Here, we demonstrated that Ser5 inhibited HIV-1-based pseudovirions bearing IAV hemagglutinin (HA); as expected, the Ser5 effect on this glycoprotein was antagonized by HIV-1 Nef protein. We found that Ser5 inhibited the virus-cell and cell-cell fusion of IAV, apparently by interacting with HA proteins. Most importantly, overexpressed and endogenous Ser5 inhibited infection by authentic IAV. Single-molecular fluorescent resonance energy transfer (smFRET) analysis further revealed that Ser5 both destabilized the pre-fusion conformation of IAV HA and inhibited the coiled-coil formation during membrane fusion. Ser5 is expressed in cultured small airway epithelial cells, as well as in immortal human cell lines. In summary, Ser5 is a host antiviral factor against IAV which acts by blocking HA-induced membrane fusion. IMPORTANCE SERINC5 (Ser5) is a cellular protein which has been found to interfere with the infectivity of HIV-1 and a number of other retroviruses. Virus particles produced in the presence of Ser5 are impaired in their ability to enter new host cells, but the mechanism of Ser5 action is not well understood. We now report that Ser5 also inhibits infectivity of Influenza A virus (IAV) and that it interferes with the conformational changes in IAV hemagglutinin protein involved in membrane fusion and virus entry. These findings indicate that the antiviral function of Ser5 extends to other viruses as well as retroviruses, and also provide some information on the molecular mechanism of its antiviral activity.
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5
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Reversible structural changes in the influenza hemagglutinin precursor at membrane fusion pH. Proc Natl Acad Sci U S A 2022; 119:e2208011119. [PMID: 35939703 PMCID: PMC9388137 DOI: 10.1073/pnas.2208011119] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Hemagglutinin (HA) is the receptor binding and membrane fusion glycoprotein of influenza virus. Like other virus fusion glycoproteins such as those of HIV and Ebola, HA is synthesized as a precursor (HA0) that requires cleavage for fusion activity and, for influenza, exposure to low pH. Studies by X-ray and cryogenic electron microscopy (cryo-EM) have characterized conformational changes in HA that occur at membrane fusion pH. Here, using cryo-EM, we report that there are extensive changes to the structure of HA0 at low pH but that, unlike the changes in HA, the changes are reversible on return to neutral pH. The low-pH structure of HA0 is considered an indicator of potential intermediates in the conformational changes in HA at fusion pH. The subunits of the influenza hemagglutinin (HA) trimer are synthesized as single-chain precursors (HA0s) that are proteolytically cleaved into the disulfide-linked polypeptides HA1 and HA2. Cleavage is required for activation of membrane fusion at low pH, which occurs at the beginning of infection following transfer of cell-surface–bound viruses into endosomes. Activation results in extensive changes in the conformation of cleaved HA. To establish the overall contribution of cleavage to the mechanism of HA-mediated membrane fusion, we used cryogenic electron microscopy (cryo-EM) to directly image HA0 at neutral and low pH. We found extensive pH-induced structural changes, some of which were similar to those described for intermediates in the refolding of cleaved HA at low pH. They involve a partial extension of the long central coiled coil formed by melting of the preexisting secondary structure, threading it between the membrane-distal domains, and subsequent refolding as extended helices. The fusion peptide, covalently linked at its N terminus, adopts an amphipathic helical conformation over part of its length and is repositioned and packed against a complementary surface groove of conserved residues. Furthermore, and in contrast to cleaved HA, the changes in HA0 structure at low pH are reversible on reincubation at neutral pH. We discuss the implications of covalently restricted HA0 refolding for the cleaved HA conformational changes that mediate membrane fusion and for the action of antiviral drug candidates and cross-reactive anti-HA antibodies that can block influenza infectivity.
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6
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Yi C, Cai C, Cheng Z, Zhao Y, Yang X, Wu Y, Wang X, Jin Z, Xiang Y, Jin M, Han L, Zhang A. Genome-wide CRISPR-Cas9 screening identifies the CYTH2 host gene as a potential therapeutic target of influenza viral infection. Cell Rep 2022; 38:110559. [PMID: 35354039 DOI: 10.1016/j.celrep.2022.110559] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Revised: 01/06/2022] [Accepted: 03/01/2022] [Indexed: 11/28/2022] Open
Abstract
Host genes critical for viral infection are effective antiviral drug targets with tremendous potential due to their universal characteristics against different subtypes of viruses and minimization of drug resistance. Accordingly, we execute a genome-wide CRISPR-Cas9 screen with multiple rounds of survival selection. Enriched in this screen are several genes critical for host sialic acid biosynthesis and transportation, including the cytohesin 2 (CYTH2), tetratricopeptide repeat protein 24 (TTC24), and N-acetylneuraminate synthase (NANS), which we confirm are responsible for efficient influenza viral infection. Moreover, we reveal that CYTH2 is required for the early stage of influenza virus infection by mediating endosomal trafficking. Furthermore, CYTH2 antagonist SecinH3 blunts influenza virus infection in vivo. In summary, these data suggest that CYTH2 is an attractive target for developing host-directed antiviral drugs and therapeutics against influenza virus infection.
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Affiliation(s)
- Chenyang Yi
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Cong Cai
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Ze Cheng
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Yifan Zhao
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Xu Yang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Yue Wu
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Xiaoping Wang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Zehua Jin
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China
| | - Yaozu Xiang
- Shanghai East Hospital, School of Life Sciences and Technology, Tongji University, Shanghai 200000, China
| | - Meilin Jin
- Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China; Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture of the People's Republic of China, Wuhan, Hubei 430070, China
| | - Li Han
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China
| | - Anding Zhang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei 430070, China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, China; Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture of the People's Republic of China, Wuhan, Hubei 430070, China.
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7
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Caffrey M, Lavie A. pH-Dependent Mechanisms of Influenza Infection Mediated by Hemagglutinin. Front Mol Biosci 2022; 8:777095. [PMID: 34977156 PMCID: PMC8718792 DOI: 10.3389/fmolb.2021.777095] [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: 09/14/2021] [Accepted: 11/23/2021] [Indexed: 11/13/2022] Open
Abstract
Influenza hemagglutinin (HA) is a viral membrane bound protein that plays a critical role in the viral life cycle by mediating entry into target cells. HA exploits the lowering of the pH in the endosomal compartment to initiate a series of conformational changes that promote access of the viral genetic material to the cytoplasm, and hence viral replication. In this review we will first discuss what is known about the structural properties of HA as a function of pH. Next, we will discuss the dynamics and intermediate states of HA. We will then discuss the specific residues that are thought to be titrated by the change in pH and possible mechanisms for the pH triggered conformational changes. Finally, we will discuss small molecules that disrupt the pH trigger and thus serve as potential therapeutic strategies to prevent influenza infection.
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Affiliation(s)
- Michael Caffrey
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL, United States
| | - Arnon Lavie
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL, United States
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8
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Eller MW, Siaw HMH, Dyer RB. Stability of HA2 Prefusion Structure and pH-Induced Conformational Changes in the HA2 Domain of H3N2 Hemagglutinin. Biochemistry 2021; 60:2623-2636. [PMID: 34435771 PMCID: PMC8485334 DOI: 10.1021/acs.biochem.1c00551] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Influenza hemagglutinin is the fusion protein that mediates fusion of the viral and host membranes through a large conformational change upon acidification in the developing endosome. The "spring-loaded" model has long been used to describe the mechanism of hemagglutinin and other type 1 viral glycoproteins. This model postulates a metastable conformation of the HA2 subunit, caged from adopting a lower-free energy conformation by the HA1 subunit. Here, using a combination of biochemical and spectroscopic methods, we study a truncated construct of HA2 (HA2*, lacking the transmembrane domain) recombinantly expressed in Escherichia coli as a model for HA2 without the influence of HA1. Our data show that HA2* folds into a conformation like that of HA2 in full length HA and forms trimers. Upon acidification, HA2* undergoes a conformational change that is consistent with the change from pre- to postfusion HA2 in HA. This conformational change is fast and occurs on a time scale that is not consistent with aggregation. These results suggest that the prefusion conformation of HA2 is stable and the change to the postfusion conformation is due to protonation of HA2 itself and not merely uncaging by HA1.
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Affiliation(s)
- Micah W Eller
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Hew Ming Helen Siaw
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - R Brian Dyer
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
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9
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Narkhede YB, Gonzalez KJ, Strauch EM. Targeting Viral Surface Proteins through Structure-Based Design. Viruses 2021; 13:v13071320. [PMID: 34372526 PMCID: PMC8310314 DOI: 10.3390/v13071320] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2021] [Revised: 06/30/2021] [Accepted: 07/01/2021] [Indexed: 12/28/2022] Open
Abstract
The emergence of novel viral infections of zoonotic origin and mutations of existing human pathogenic viruses represent a serious concern for public health. It warrants the establishment of better interventions and protective therapies to combat the virus and prevent its spread. Surface glycoproteins catalyzing the fusion of viral particles and host cells have proven to be an excellent target for antivirals as well as vaccines. This review focuses on recent advances for computational structure-based design of antivirals and vaccines targeting viral fusion machinery to control seasonal and emerging respiratory viruses.
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Affiliation(s)
- Yogesh B Narkhede
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA 30602, USA;
| | - Karen J Gonzalez
- Institute of Bioinformatics, University of Georgia, Athens, GA 30602, USA;
| | - Eva-Maria Strauch
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, GA 30602, USA;
- Institute of Bioinformatics, University of Georgia, Athens, GA 30602, USA;
- Correspondence:
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10
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Lu M. Single-Molecule FRET Imaging of Virus Spike-Host Interactions. Viruses 2021; 13:v13020332. [PMID: 33669922 PMCID: PMC7924862 DOI: 10.3390/v13020332] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Revised: 02/18/2021] [Accepted: 02/18/2021] [Indexed: 02/07/2023] Open
Abstract
As a major surface glycoprotein of enveloped viruses, the virus spike protein is a primary target for vaccines and anti-viral treatments. Current vaccines aiming at controlling the COVID-19 pandemic are mostly directed against the SARS-CoV-2 spike protein. To promote virus entry and facilitate immune evasion, spikes must be dynamic. Interactions with host receptors and coreceptors trigger a cascade of conformational changes/structural rearrangements in spikes, which bring virus and host membranes in proximity for membrane fusion required for virus entry. Spike-mediated viral membrane fusion is a dynamic, multi-step process, and understanding the structure–function-dynamics paradigm of virus spikes is essential to elucidate viral membrane fusion, with the ultimate goal of interventions. However, our understanding of this process primarily relies on individual structural snapshots of endpoints. How these endpoints are connected in a time-resolved manner, and the order and frequency of conformational events underlying virus entry, remain largely elusive. Single-molecule Förster resonance energy transfer (smFRET) has provided a powerful platform to connect structure–function in motion, revealing dynamic aspects of spikes for several viruses: SARS-CoV-2, HIV-1, influenza, and Ebola. This review focuses on how smFRET imaging has advanced our understanding of virus spikes’ dynamic nature, receptor-binding events, and mechanism of antibody neutralization, thereby informing therapeutic interventions.
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Affiliation(s)
- Maolin Lu
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06536, USA
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11
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Gao J, Gui M, Xiang Y. Structural intermediates in the low pH-induced transition of influenza hemagglutinin. PLoS Pathog 2020; 16:e1009062. [PMID: 33253316 PMCID: PMC7728236 DOI: 10.1371/journal.ppat.1009062] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2020] [Revised: 12/10/2020] [Accepted: 10/09/2020] [Indexed: 12/16/2022] Open
Abstract
The hemagglutinin (HA) glycoproteins of influenza viruses play a key role in binding host cell receptors and in mediating virus-host cell membrane fusion during virus infection. Upon virus entry, HA is triggered by low pH and undergoes large structural rearrangements from a prefusion state to a postfusion state. While structures of prefusion state and postfusion state of HA have been reported, the intermediate structures remain elusive. Here, we report two distinct low pH intermediate conformations of the influenza virus HA using cryo-electron microscopy (cryo-EM). Our results show that a decrease in pH from 7.8 to 5.2 triggers the release of fusion peptides from the binding pockets and then causes a dramatic conformational change in the central helices, in which the membrane-proximal ends of the central helices unwind to an extended form. Accompanying the conformational changes of the central helices, the stem region of the HA undergoes an anticlockwise rotation of 9.5 degrees and a shift of 15 Å. The HA head, after being stabilized by an antibody, remains unchanged compared to the neutral pH state. Thus, the conformational change of the HA stem region observed in our research is likely to be independent of the HA head. These results provide new insights into the structural transition of HA during virus entry.
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Affiliation(s)
- Jingjing Gao
- Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Center for Infectious Disease Research, Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
| | - Miao Gui
- Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Center for Infectious Disease Research, Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
- * E-mail: (MG); (YX)
| | - Ye Xiang
- Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, Center for Infectious Disease Research, Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing, China
- * E-mail: (MG); (YX)
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12
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Lim K, Kodera N, Wang H, Mohamed MS, Hazawa M, Kobayashi A, Yoshida T, Hanayama R, Yano S, Ando T, Wong RW. High-Speed AFM Reveals Molecular Dynamics of Human Influenza A Hemagglutinin and Its Interaction with Exosomes. NANO LETTERS 2020; 20:6320-6328. [PMID: 32787163 DOI: 10.1021/acs.nanolett.0c01755] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Influenza A hemagglutinin (HA) is one of the crucial virulence factors that mediate host tropism and viral infectivity. Presently, the mechanism of the fusogenic transition of HA remains elusive. Here, we used high-speed atomic force microscopy (HS-AFM) to decipher the molecular dynamics of HA and its interaction with exosomes. Our data reveal that the native conformation of HA in the neutral buffer is ellipsoidal, and HA undergoes a conformational change in an acidic buffer. Real-time visualization of the fusogenic transition by HS-AFM suggests that the mechanism is possibly fit to the "uncaging" model, and HA intermediate appears as Y-shaped. A firm interaction between the HA and exosome in an acidic buffer indicates the insertion of a fusion peptide into the exosomal layer and subsequently destabilizes the layer, resulting in the deformation or rupture of exosomes, releasing exosomal contents. In contrast, the HA-exosome interaction is weak in a neutral buffer because the interaction is mediated by weak bonds between the HA receptor-binding site and receptors on the exosome.
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Affiliation(s)
- Keesiang Lim
- WPI-Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
| | - Noriyuki Kodera
- WPI-Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
| | - Hanbo Wang
- Cell-Bionomics Research Unit, Institute for Frontier Science Initiative (INFINITI), Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan
| | - Mahmoud Shaaban Mohamed
- Cell-Bionomics Research Unit, Institute for Frontier Science Initiative (INFINITI), Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan
| | - Masaharu Hazawa
- WPI-Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
- Cell-Bionomics Research Unit, Institute for Frontier Science Initiative (INFINITI), Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan
| | - Akiko Kobayashi
- Cell-Bionomics Research Unit, Institute for Frontier Science Initiative (INFINITI), Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan
| | - Takeshi Yoshida
- WPI-Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
- Department of Immunology, Kanazawa University Graduate School of Medical Sciences, 13-1 Takara, Kanazawa, Ishikawa 920-8640, Japan
| | - Rikinari Hanayama
- WPI-Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
- Department of Immunology, Kanazawa University Graduate School of Medical Sciences, 13-1 Takara, Kanazawa, Ishikawa 920-8640, Japan
| | - Seiji Yano
- WPI-Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
- Division of Medical Oncology, Cancer Research Institute, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan
| | - Toshio Ando
- WPI-Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
| | - Richard W Wong
- WPI-Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan
- Cell-Bionomics Research Unit, Institute for Frontier Science Initiative (INFINITI), Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan
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13
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Benhaim MA, Mangala Prasad V, Garcia NK, Guttman M, Lee KK. Structural monitoring of a transient intermediate in the hemagglutinin fusion machinery on influenza virions. SCIENCE ADVANCES 2020; 6:eaaz8822. [PMID: 32494683 PMCID: PMC7190341 DOI: 10.1126/sciadv.aaz8822] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Accepted: 02/05/2020] [Indexed: 05/16/2023]
Abstract
The influenza virus hemagglutinin (HA) fusion protein has long been viewed as a "spring-loaded" fusion machine whereby activation at low pH initiates a rapid and irreversible cascade of conformational changes that drives the membrane fusion reaction. This mechanism has shaped our understanding of how type 1 viral fusion proteins function as a whole. Experimental limitations have hindered efforts to expand our mechanistic and structural understanding of viral membrane fusion. Here, we used pulse-labeling hydrogen/deuterium exchange mass spectrometry and cryo-electron tomography to monitor and characterize the structural dynamics of HA during fusion activation on intact virions. Our data reveal how concurrent reorganizations at the HA1 receptor binding domain interface and HA2 fusion subunit produce a dynamic fusion intermediate ensemble in full-length HA. The soluble HA ectodomain transitions directly to the postfusion state with no observable intermediate.
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Affiliation(s)
- M. A. Benhaim
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA
| | - V. Mangala Prasad
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA
| | - N. K. Garcia
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA
| | - M. Guttman
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA
| | - K. K. Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA
- Biological Physics, Structure and Design Graduate Program, University of Washington, Seattle, WA, USA
- Department of Microbiology, University of Washington, Seattle, WA, USA
- Corresponding author.
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14
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Benhaim MA, Lee KK. New Biophysical Approaches Reveal the Dynamics and Mechanics of Type I Viral Fusion Machinery and Their Interplay with Membranes. Viruses 2020; 12:E413. [PMID: 32276357 PMCID: PMC7232462 DOI: 10.3390/v12040413] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 04/04/2020] [Accepted: 04/04/2020] [Indexed: 12/27/2022] Open
Abstract
Protein-mediated membrane fusion is a highly regulated biological process essential for cellular and organismal functions and infection by enveloped viruses. During viral entry the membrane fusion reaction is catalyzed by specialized protein machinery on the viral surface. These viral fusion proteins undergo a series of dramatic structural changes during membrane fusion where they engage, remodel, and ultimately fuse with the host membrane. The structural and dynamic nature of these conformational changes and their impact on the membranes have long-eluded characterization. Recent advances in structural and biophysical methodologies have enabled researchers to directly observe viral fusion proteins as they carry out their functions during membrane fusion. Here we review the structure and function of type I viral fusion proteins and mechanisms of protein-mediated membrane fusion. We highlight how recent technological advances and new biophysical approaches are providing unprecedented new insight into the membrane fusion reaction.
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Affiliation(s)
- Mark A. Benhaim
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195-7610, USA;
| | - Kelly K. Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195-7610, USA;
- Biological Physics Structure and Design Program, University of Washington, Seattle, WA 98195-7610, USA
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15
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Antanasijevic A, Durst MA, Lavie A, Caffrey M. Identification of a pH sensor in Influenza hemagglutinin using X-ray crystallography. J Struct Biol 2019; 209:107412. [PMID: 31689502 PMCID: PMC7111647 DOI: 10.1016/j.jsb.2019.107412] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Revised: 10/29/2019] [Accepted: 10/30/2019] [Indexed: 11/15/2022]
Abstract
X-ray crystallography identifies a conserved histidine, HA1-H38, that changes side chain conformation at low pH. We attribute the observed conformational change to cation-cation repulsion between protonated HA1-H18 and HA1-H38. We suggest that the HA1-H18 and HA1-H38 pair plays a role in the pathway toward the postfusion conformation of HA.
Hemagglutnin (HA) mediates entry of influenza virus through a series of conformational changes triggered by the low pH of the endosome. The residue or combination of residues acting as pH sensors has not yet been fully elucidated. In this work, we assay pH effects on the structure of H5 HA by soaking HA crystallized at pH 6.5 in a series of buffers with lower pH, mimicking the conditions of the endosome. We find that HA1-H38, which is conserved in Group 1 HA, undergoes a striking change in side chain conformation, which we attribute to its protonation and cation-cation repulsion with conserved HA1-H18. This work suggests that x-ray crystallography can be applied for studying small-scale pH-induced conformational changes providing valuable information on the location of pH sensors in HA. Importantly, the observed change in HA1-H38 conformation is further evidence that the pH-induced conformational changes of HA are the result of a series of protonation events to conserved and non-conserved pH sensors.
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Affiliation(s)
- Aleksandar Antanasijevic
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 900 S Ashland Ave, 60607 Chicago, USA
| | - Matthew A Durst
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 900 S Ashland Ave, 60607 Chicago, USA
| | - Arnon Lavie
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 900 S Ashland Ave, 60607 Chicago, USA.
| | - Michael Caffrey
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 900 S Ashland Ave, 60607 Chicago, USA.
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16
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Developments in single-molecule and single-particle fluorescence-based approaches for studying viral envelope glycoprotein dynamics and membrane fusion. Adv Virus Res 2019; 104:123-146. [PMID: 31439147 DOI: 10.1016/bs.aivir.2019.05.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Fusion of viral and cellular membranes is an essential step in the entry pathway of all enveloped viruses. This is a dynamic and multistep process, which has been extensively studied, resulting in the endpoints of the reaction being firmly established, and many essential cellular factors identified. What remains is to elucidate the dynamic events that underlie this process, including the order and timing of glycoprotein conformational changes, receptor-binding events, and movement of the glycoprotein on the surface of the virion. Due to the inherently asynchronous nature of these dynamics, there has been an increased focus on the study of single virions and single molecules. These techniques provide researchers the high precision and resolution necessary to bridge the gaps in our understanding of viral membrane fusion. This review highlights the advancement of single-molecule and single-particle fluorescence-based techniques, with a specific focus on how these techniques have been used to study the dynamic nature of the viral fusion pathway.
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17
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Kosik I, Yewdell JW. Influenza Hemagglutinin and Neuraminidase: Yin⁻Yang Proteins Coevolving to Thwart Immunity. Viruses 2019; 11:E346. [PMID: 31014029 PMCID: PMC6520700 DOI: 10.3390/v11040346] [Citation(s) in RCA: 116] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Revised: 04/11/2019] [Accepted: 04/13/2019] [Indexed: 01/04/2023] Open
Abstract
Influenza A virions possess two surface glycoproteins-the hemagglutinin (HA) and neuraminidase (NA)-which exert opposite functions. HA attaches virions to cells by binding to terminal sialic acid residues on glycoproteins/glycolipids to initiate the infectious cycle, while NA cleaves terminal sialic acids, releasing virions to complete the infectious cycle. Antibodies specific for HA or NA can protect experimental animals from IAV pathogenesis and drive antigenic variation in their target epitopes that impairs vaccine effectiveness in humans. Here, we review progress in understanding HA/NA co-evolution as each acquires epistatic mutations to restore viral fitness to mutants selected in the other protein by host innate or adaptive immune pressure. We also discuss recent exciting findings that antibodies to HA can function in vivo by blocking NA enzyme activity to prevent nascent virion release and enhance Fc receptor-based activation of innate immune cells.
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Affiliation(s)
- Ivan Kosik
- Laboratory of Viral Diseases, NIAID, NIH, Bethesda, MD 20892, USA.
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18
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Chae W, Kim P, Hwang BJ, Seong BL. Universal monoclonal antibody-based influenza hemagglutinin quantitative enzyme-linked immunosorbent assay. Vaccine 2019; 37:1457-1466. [DOI: 10.1016/j.vaccine.2019.01.068] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2018] [Revised: 01/22/2019] [Accepted: 01/23/2019] [Indexed: 01/19/2023]
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19
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Das DK, Govindan R, Nikić-Spiegel I, Krammer F, Lemke EA, Munro JB. Direct Visualization of the Conformational Dynamics of Single Influenza Hemagglutinin Trimers. Cell 2018; 174:926-937.e12. [PMID: 29961575 PMCID: PMC6086748 DOI: 10.1016/j.cell.2018.05.050] [Citation(s) in RCA: 102] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 05/17/2018] [Accepted: 05/24/2018] [Indexed: 01/02/2023]
Abstract
Influenza hemagglutinin (HA) is the canonical type I viral envelope glycoprotein and provides a template for the membrane-fusion mechanisms of numerous viruses. The current model of HA-mediated membrane fusion describes a static "spring-loaded" fusion domain (HA2) at neutral pH. Acidic pH triggers a singular irreversible conformational rearrangement in HA2 that fuses viral and cellular membranes. Here, using single-molecule Förster resonance energy transfer (smFRET)-imaging, we directly visualized pH-triggered conformational changes of HA trimers on the viral surface. Our analyses reveal reversible exchange between the pre-fusion and two intermediate conformations of HA2. Acidification of pH and receptor binding shifts the dynamic equilibrium of HA2 in favor of forward progression along the membrane-fusion reaction coordinate. Interaction with the target membrane promotes irreversible transition of HA2 to the post-fusion state. The reversibility of HA2 conformation may protect against transition to the post-fusion state prior to arrival at the target membrane.
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Affiliation(s)
- Dibyendu Kumar Das
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, MA 02111, USA.
| | - Ramesh Govindan
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, MA 02111, USA
| | - Ivana Nikić-Spiegel
- Werner Reichardt Centre for Integrative Neuroscience, University of Tuebingen, 72076 Tuebingen, Germany
| | - Florian Krammer
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Edward A Lemke
- Departments of Biology and Chemistry, Pharmacy, and Geosciences, Johannes Gutenberg-University Mainz, Johannes-von-Mullerweg 6, 55128 Mainz, Germany; Institute of Molecular Biology (IMB), Ackermannweg 4, 55128 Mainz, Germany; Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - James B Munro
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine and Sackler School of Graduate Biomedical Sciences, Boston, MA 02111, USA.
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20
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Di Lella S, Herrmann A, Mair CM. Modulation of the pH Stability of Influenza Virus Hemagglutinin: A Host Cell Adaptation Strategy. Biophys J 2017; 110:2293-2301. [PMID: 27276248 DOI: 10.1016/j.bpj.2016.04.035] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Revised: 03/15/2016] [Accepted: 04/25/2016] [Indexed: 12/31/2022] Open
Abstract
Proteins undergo dynamic structural changes to function within the range of physical and chemical conditions of their microenvironments. Changes in these environments affect their activity unless the respective mutations preserve their proper function. Here, we examine the influenza A virus spike protein hemagglutinin (HA), which undergoes a dynamic conformational change that is essential to the viral life cycle and is dependent on endosomal pH. Since the cells of different potential hosts exhibit different levels of pH, the virus can only cross species barriers if HA undergoes mutations that still permit the structural change to occur. This key event occurs after influenza A enters the host cell via the endocytic route, during its intracellular transport inside endosomes. The acidic pH inside these vesicles triggers a major structural transition of HA that induces fusion of the viral envelope and the endosomal membrane, and permits the release of the viral genome. HA experiences specific mutations that alter its pH stability and allow the conformational changes required for fusion in different hosts, despite the differences in the degree of acidification of their endosomes. Experimental and theoretical studies over the past few years have provided detailed insights into the structural aspects of the mutational changes that alter its susceptibility to different pH thresholds. We will illustrate how such mutations modify the protein's structure and consequently its pH stability. These changes make HA an excellent model of the way subtle structural modifications affect a protein's stability and enable it to function in diverse environments.
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Affiliation(s)
- Santiago Di Lella
- Institute of Biology, Humboldt Universität zu Berlin, Berlin, Germany; Departamento de Química Biológica e IQUIBICEN-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad de Buenos Aires, Argentina
| | - Andreas Herrmann
- Institute of Biology, Humboldt Universität zu Berlin, Berlin, Germany
| | - Caroline M Mair
- Institute of Biology, Humboldt Universität zu Berlin, Berlin, Germany.
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21
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Desai TM, Marin M, Mason C, Melikyan GB. pH regulation in early endosomes and interferon-inducible transmembrane proteins control avian retrovirus fusion. J Biol Chem 2017; 292:7817-7827. [PMID: 28341742 DOI: 10.1074/jbc.m117.783878] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Revised: 03/22/2017] [Indexed: 01/09/2023] Open
Abstract
Enveloped viruses infect host cells by fusing their membranes with those of the host cell, a process mediated by viral glycoproteins upon binding to cognate host receptors or entering into acidic intracellular compartments. Whereas the effect of receptor density on viral infection has been well studied, the role of cell type-specific factors/processes, such as pH regulation, has not been characterized in sufficient detail. Here, we examined the effects of cell-extrinsic factors (buffer environment) and cell-intrinsic factors (interferon-inducible transmembrane proteins, IFITMs), on the pH regulation in early endosomes and on the efficiency of acid-dependent fusion of the avian sarcoma and leukosis virus (ASLV), with endosomes. First, we found that a modest elevation of external pH can raise the pH in early endosomes in a cell type-dependent manner and thereby delay the acid-induced fusion of endocytosed ASLV. Second, we observed a cell type-dependent delay between the low pH-dependent and temperature-dependent steps of viral fusion, consistent with the delayed enlargement of the fusion pore. Third, ectopic expression of IFITMs, known to potently block influenza virus fusion with late compartments, was found to only partially inhibit ASLV fusion with early endosomes. Interestingly, IFITM expression promoted virus uptake and the acidification of endosomal compartments, resulting in an accelerated fusion rate when driven by the glycosylphosphatidylinositol-anchored, but not by the transmembrane isoform of the ASLV receptor. Collectively, these results highlight the role of cell-extrinsic and cell-intrinsic factors in regulating the efficiency and kinetics of virus entry and fusion with target cells.
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Affiliation(s)
- Tanay M Desai
- From the Division of Pediatric Infectious Diseases, Emory University School of Medicine, Atlanta, Georgia 30322 and
| | - Mariana Marin
- From the Division of Pediatric Infectious Diseases, Emory University School of Medicine, Atlanta, Georgia 30322 and
| | - Caleb Mason
- From the Division of Pediatric Infectious Diseases, Emory University School of Medicine, Atlanta, Georgia 30322 and
| | - Gregory B Melikyan
- From the Division of Pediatric Infectious Diseases, Emory University School of Medicine, Atlanta, Georgia 30322 and .,the Children's Healthcare of Atlanta, Atlanta, Georgia 300322
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22
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Sequential activation of the three protomers in the Moloney murine leukemia virus Env. Proc Natl Acad Sci U S A 2017; 114:2723-2728. [PMID: 28223490 DOI: 10.1073/pnas.1617264114] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Viral membrane fusion proteins of class I are trimers in which the protomeric unit is a complex of a surface subunit (SU) and a fusion active transmembrane subunit (TM). Here we have studied how the protomeric units of Moloney murine leukemia virus envelope protein (Env) are activated in relation to each other, sequentially or simultaneously. We followed the isomerization of the SU-TM disulfide and subsequent SU release from Env with biochemical methods and found that this early activation step occurred sequentially in the three protomers, generating two asymmetric oligomer intermediates according to the scheme (SU-TM)3 → (SU-TM)2TM → (SU-TM)TM2 → TM3 This was the case both when activation was triggered in vitro by depleting stabilizing Ca2+ from solubilized Env and when viral Env was receptor triggered on rat XC cells. In the latter case, the activation reaction was too fast for direct observation of the intermediates, but they could be caught by alkylation of the isomerization active thiol.
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23
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Blijleven JS, Boonstra S, Onck PR, van der Giessen E, van Oijen AM. Mechanisms of influenza viral membrane fusion. Semin Cell Dev Biol 2016; 60:78-88. [PMID: 27401120 DOI: 10.1016/j.semcdb.2016.07.007] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Revised: 06/28/2016] [Accepted: 07/07/2016] [Indexed: 11/18/2022]
Abstract
Influenza viral particles are enveloped by a lipid bilayer. A major step in infection is fusion of the viral and host cellular membranes, a process with large kinetic barriers. Influenza membrane fusion is catalyzed by hemagglutinin (HA), a class I viral fusion protein activated by low pH. The exact nature of the HA conformational changes that deliver the energy required for fusion remains poorly understood. This review summarizes our current knowledge of HA structure and dynamics, describes recent single-particle experiments and modeling studies, and discusses their role in understanding how multiple HAs mediate fusion. These approaches provide a mechanistic picture in which HAs independently and stochastically insert into the target membrane, forming a cluster of HAs that is collectively able to overcome the barrier to membrane fusion. The new experimental and modeling approaches described in this review hold promise for a more complete understanding of other viral fusion systems and the protein systems responsible for cellular fusion.
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Affiliation(s)
- Jelle S Blijleven
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Sander Boonstra
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Patrick R Onck
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Erik van der Giessen
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Antoine M van Oijen
- School of Chemistry, Faculty of Science, Medicine and Health, University of Wollongong, NSW 2522, Australia.
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24
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Intravirion cohesion of matrix protein M1 with ribonucleocapsid is a prerequisite of influenza virus infectivity. Virology 2016; 492:187-96. [DOI: 10.1016/j.virol.2016.02.021] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 02/21/2016] [Accepted: 02/22/2016] [Indexed: 11/18/2022]
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25
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Dynamic Viral Glycoprotein Machines: Approaches for Probing Transient States That Drive Membrane Fusion. Viruses 2016; 8:v8010015. [PMID: 26761026 PMCID: PMC4728575 DOI: 10.3390/v8010015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Revised: 12/11/2015] [Accepted: 12/31/2015] [Indexed: 01/10/2023] Open
Abstract
The fusion glycoproteins that decorate the surface of enveloped viruses undergo dramatic conformational changes in the course of engaging with target cells through receptor interactions and during cell entry. These refolding events ultimately drive the fusion of viral and cellular membranes leading to delivery of the genetic cargo. While well-established methods for structure determination such as X-ray crystallography have provided detailed structures of fusion proteins in the pre- and post-fusion fusion states, to understand mechanistically how these fusion glycoproteins perform their structural calisthenics and drive membrane fusion requires new analytical approaches that enable dynamic intermediate states to be probed. Methods including structural mass spectrometry, small-angle X-ray scattering, and electron microscopy have begun to provide new insight into pathways of conformational change and fusion protein function. In combination, the approaches provide a significantly richer portrait of viral fusion glycoprotein structural variation and fusion activation as well as inhibition by neutralizing agents. Here recent studies that highlight the utility of these complementary approaches will be reviewed with a focus on the well-characterized influenza virus hemagglutinin fusion glycoprotein system.
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26
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Fontana J, Steven AC. Influenza virus-mediated membrane fusion: Structural insights from electron microscopy. Arch Biochem Biophys 2015; 581:86-97. [PMID: 25958107 DOI: 10.1016/j.abb.2015.04.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Revised: 04/21/2015] [Accepted: 04/27/2015] [Indexed: 12/26/2022]
Abstract
Influenza virus, the causative agent of flu, enters the host cell by endocytosis. The low pH encountered inside endosomes triggers conformational changes in the viral glycoprotein hemagglutinin (HA), that mediate fusion of the viral and cellular membranes. This releases the viral genome into the cytoplasm of the infected cell, establishing the onset of the replication cycle. To investigate the structural basis of HA-mediated membrane fusion, a number of techniques have been employed. These include X-ray crystallography, which has provided atomic models of the HA ectodomain in its initial (pre-fusion) state and of part of HA in its final (post-fusion) state. However, this left an information deficit concerning many other aspects of the fusion process. Electron microscopy (EM) approaches are helping to fill this void. For example, influenza virions at neutral pH have been imaged by cryo-EM and cryo-electron tomography (cryo-ET); thin section EM has shown that influenza viruses enter the cell by endocytosis; the large-scale structural changes in HA when virions are exposed to low pH (pre-fusion to post-fusion states) have been visualized by negative staining and cryo-EM; acidification also induces structural changes in the M1 matrix layer and its separation from the viral envelope; intermediate HA conformations between its pre- and post-fusion states have been detected by cryo-ET supplemented with subtomogram averaging; and fusion of influenza virions with liposomes has been visualized by cryo-ET. In this review, we survey EM-based contributions towards the characterization of influenza virus-mediated membrane fusion and anticipate the potential for future developments.
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Affiliation(s)
- Juan Fontana
- Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Alasdair C Steven
- Laboratory of Structural Biology Research, National Institute of Arthritis, Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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27
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Garcia NK, Guttman M, Ebner JL, Lee KK. Dynamic changes during acid-induced activation of influenza hemagglutinin. Structure 2015; 23:665-76. [PMID: 25773144 PMCID: PMC4499473 DOI: 10.1016/j.str.2015.02.006] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2014] [Revised: 02/04/2015] [Accepted: 02/09/2015] [Indexed: 11/18/2022]
Abstract
Influenza hemagglutinin (HA) mediates virus attachment to host cells and fusion of the viral and endosomal membranes during entry. While high-resolution structures are available for the pre-fusion HA ectodomain and the post-fusion HA2 subunit, the sequence of conformational changes during HA activation has eluded structural characterization. Here, we apply hydrogen-deuterium exchange with mass spectrometry to examine changes in structural dynamics of the HA ectodomain at various stages of activation, and compare the soluble ectodomain with intact HA on virions. At pH conditions approaching activation (pH 6.0-5.5) HA exhibits increased dynamics at the fusion peptide and neighboring regions, while the interface between receptor binding subunits (HA1) becomes stabilized. In contrast to many activation models, these data suggest that HA responds to endosomal acidification by releasing the fusion peptide prior to HA1 uncaging and the spring-loaded refolding of HA2. This staged process may facilitate efficient HA-mediated fusion.
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Affiliation(s)
- Natalie K Garcia
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Miklos Guttman
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Jamie L Ebner
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Kelly K Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA.
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28
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Dash P, Thomas PG. Host detection and the stealthy phenotype in influenza virus infection. Curr Top Microbiol Immunol 2015; 386:121-47. [PMID: 25038940 DOI: 10.1007/82_2014_412] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The innate host response to influenza virus infection plays a critical role in determining the subsequent course of infection and the clinical outcome of disease. The host has a diverse array of detection and effector mechanisms that are able to recognize and initiate effective antiviral responses. In opposition, the virus utilizes a number of distinct mechanisms to evade host detection and effector activity in order to remain "stealthy" throughout its replication cycle. In this review, we describe these host and viral mechanisms, including the major pattern recognition receptor families (the TLRs, NLRs, and RLRs) in the host and the specific viral proteins such as NS1 that are key players in this interaction. Additionally, we explore nonreductive mechanisms of viral immune evasion and propose areas important for future inquiry.
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Affiliation(s)
- Pradyot Dash
- Department of Immunology, St. Jude Children's Research Hospital, Memphis, TN, 38105, USA
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A histidine residue of the influenza virus hemagglutinin controls the pH dependence of the conformational change mediating membrane fusion. J Virol 2014; 88:13189-200. [PMID: 25187542 DOI: 10.1128/jvi.01704-14] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The conformational change of the influenza virus hemagglutinin (HA) protein mediating the fusion between the virus envelope and the endosomal membrane was hypothesized to be induced by protonation of specific histidine residues since their pKas match the pHs of late endosomes (pK(a) of ∼ 6.0). However, such critical key histidine residues remain to be identified. We investigated the highly conserved His184 at the HA1-HA1 interface and His110 at the HA1-HA2 interface of highly pathogenic H5N1 HA as potential pH sensors. By replacing both histidines with different amino acids and analyzing the effect of these mutations on conformational change and fusion, we found that His184, but not His110, plays an essential role in the pH dependence of the conformational change of HA. Computational modeling of the protonated His184 revealed that His184 is central in a conserved interaction network possibly regulating the pH dependence of conformational change via its pKa. As the propensity of histidine to get protonated largely depends on its local environment, mutation of residues in the vicinity of histidine may affect its pK(a). The HA of highly pathogenic H5N1 viruses carries a Glu-to-Arg mutation at position 216 close to His184. By mutation of residue 216 in the highly pathogenic as well as the low pathogenic H5 HA, we observed a significant influence on the pH dependence of conformational change and fusion. These results are in support of a pK(a)-modulating effect of neighboring residues. IMPORTANCE The main pathogenic determinant of influenza viruses, the hemagglutinin (HA) protein, triggers a key step of the infection process: the fusion of the virus envelope with the endosomal membrane releasing the viral genome. Whereas essential aspects of the fusion-inducing mechanism of HA at low pH are well understood, the molecular trigger of the pH-dependent conformational change inducing fusion has been unclear. We provide evidence that His184 regulates the pH dependence of the HA conformational change via its pK(a). Mutations of neighboring residues which may affect the pK(a) of His184 could play an important role in virus adaptation to a specific host. We suggest that mutation of neighboring residue 216, which is present in all highly pathogenic phenotypes of H5N1 influenza virus strains, contributed to the adaptation of these viruses to the human host via its effect on the pKa of His184.
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Iversen L, Tu HL, Lin WC, Christensen SM, Abel SM, Iwig J, Wu HJ, Gureasko J, Rhodes C, Petit RS, Hansen SD, Thill P, Yu CH, Stamou D, Chakraborty AK, Kuriyan J, Groves JT. Molecular kinetics. Ras activation by SOS: allosteric regulation by altered fluctuation dynamics. Science 2014; 345:50-4. [PMID: 24994643 DOI: 10.1126/science.1250373] [Citation(s) in RCA: 103] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Activation of the small guanosine triphosphatase H-Ras by the exchange factor Son of Sevenless (SOS) is an important hub for signal transduction. Multiple layers of regulation, through protein and membrane interactions, govern activity of SOS. We characterized the specific activity of individual SOS molecules catalyzing nucleotide exchange in H-Ras. Single-molecule kinetic traces revealed that SOS samples a broad distribution of turnover rates through stochastic fluctuations between distinct, long-lived (more than 100 seconds), functional states. The expected allosteric activation of SOS by Ras-guanosine triphosphate (GTP) was conspicuously absent in the mean rate. However, fluctuations into highly active states were modulated by Ras-GTP. This reveals a mechanism in which functional output may be determined by the dynamical spectrum of rates sampled by a small number of enzymes, rather than the ensemble average.
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Affiliation(s)
- Lars Iversen
- Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Hsiung-Lin Tu
- Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Wan-Chen Lin
- Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Sune M Christensen
- Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Steven M Abel
- Department of Chemical Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA
| | - Jeff Iwig
- Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Hung-Jen Wu
- Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Jodi Gureasko
- Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Christopher Rhodes
- Department of Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Rebecca S Petit
- Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Scott D Hansen
- Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Peter Thill
- Department of Chemistry, MIT, Cambridge, MA 02139, USA
| | - Cheng-Han Yu
- Mechanobiology Institute, National University of Singapore, Singapore
| | - Dimitrios Stamou
- Department of Chemistry and Nano-Science Center, University of Copenhagen, Copenhagen, Denmark
| | - Arup K Chakraborty
- Department of Chemical Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA. Department of Chemistry, MIT, Cambridge, MA 02139, USA. Department of Biological Engineering, MIT, Cambridge, MA 02139, USA. Ragon Institute of Massachusetts General Hospital, MIT, and Harvard, Cambridge, MA 02139, USA. Department of Physics, MIT, Cambridge, MA 02139, USA. Institute for Medical Engineering and Science, MIT, Cambridge, MA 02139, USA
| | - John Kuriyan
- Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA. Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA. Physical Biosciences and Materials Sciences Divisions, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Jay T Groves
- Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA. Mechanobiology Institute, National University of Singapore, Singapore. Physical Biosciences and Materials Sciences Divisions, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. Berkeley Education Alliance for Research in Singapore, 1 Create Way, CREATE tower level 11, University Town, Singapore 138602.
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31
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Zhou Y, Wu C, Zhao L, Huang N. Exploring the early stages of the pH-induced conformational change of influenza hemagglutinin. Proteins 2014; 82:2412-28. [PMID: 24854389 DOI: 10.1002/prot.24606] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Revised: 04/15/2014] [Accepted: 05/12/2014] [Indexed: 11/09/2022]
Abstract
Hemagglutinin (HA) mediates the membrane fusion process of influenza virus through its pH-induced conformational change. However, it remains challenging to study its structure reorganization pathways in atomic details. Here, we first applied continuous constant pH molecular dynamics approach to predict the pK(a) values of titratable residues in H2 subtype HA. The calculated net-charges in HA1 globular heads increase from 0e (pH 7.5) to +14e (pH 4.5), indicating that the charge repulsion drives the detrimerization of HA globular domains. In HA2 stem regions, critical pH sensors, such as Glu103(2), His18(1), and Glu89(1), are identified to facilitate the essential structural reorganizations in the fusing pathways, including fusion peptide release and interhelical loop transition. To probe the contribution of identified pH sensors and unveil the early steps of pH-induced conformational change, we carried out conventional molecular dynamics simulations in explicit water with determined protonation state for each titratable residue in different environmental pH conditions. Particularly, energy barriers involving previously uncharacterized hydrogen bonds and hydrophobic interactions are identified in the fusion peptide release pathway. Nevertheless, comprehensive comparisons across HA family members indicate that different HA subtypes might employ diverse pH sensor groups along with different fusion pathways. Finally, we explored the fusion inhibition mechanism of antibody CR6261 and small molecular inhibitor TBHQ, and discovered a novel druggable pocket in H2 and H5 subtypes. Our results provide the underlying mechanism for the pH-driven conformational changes and also novel insight for anti-flu drug development.
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Affiliation(s)
- Yu Zhou
- College of Life Sciences, Beijing Normal University, Beijing, 100875, China; National Institute of Biological Sciences, Beijing, Zhongguancun Life Science Park, Beijing, 102206, China
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32
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Edinger TO, Pohl MO, Stertz S. Entry of influenza A virus: host factors and antiviral targets. J Gen Virol 2013; 95:263-277. [PMID: 24225499 DOI: 10.1099/vir.0.059477-0] [Citation(s) in RCA: 159] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Influenza virus is a major human pathogen that causes annual epidemics and occasional pandemics. Moreover, the virus causes outbreaks in poultry and other animals, such as pigs, requiring costly and laborious countermeasures. Therefore, influenza virus has a substantial impact on health and the global economy. Here, we review entry of this important pathogen into target cells, an essential process by which viral genomes are delivered from extracellular virions to sites of transcription/replication in the cell nucleus. We summarize current knowledge on the interaction of influenza viruses with their receptor, sialic acid, and highlight the ongoing search for additional receptors. We describe receptor-mediated endocytosis and the recently discovered macropinocytosis as alternative virus uptake pathways, and illustrate the subsequent endosomal trafficking of the virus with advanced live microscopy techniques. Release of virus from the endosome and import of the viral ribonucleoproteins into the host cell nucleus are also outlined. Although a focus has been on viral protein function during entry, recent studies have revealed exciting information on cellular factors required for influenza virus entry. We highlight these, and discuss established entry inhibitors targeting viral and host factors, as well as the latest prospects for designing novel 'anti-entry' compounds. New entry inhibitors are of particular importance for current efforts to develop the next generation of anti-influenza drugs - entry is the first essential step of virus replication and is an ideal target to block infection efficiently.
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Affiliation(s)
- Thomas O Edinger
- Institute of Medical Virology, University of Zurich, 8057 Zurich, Switzerland
| | - Marie O Pohl
- Institute of Medical Virology, University of Zurich, 8057 Zurich, Switzerland
| | - Silke Stertz
- Institute of Medical Virology, University of Zurich, 8057 Zurich, Switzerland
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33
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Mair CM, Ludwig K, Herrmann A, Sieben C. Receptor binding and pH stability - how influenza A virus hemagglutinin affects host-specific virus infection. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:1153-68. [PMID: 24161712 DOI: 10.1016/j.bbamem.2013.10.004] [Citation(s) in RCA: 122] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 09/26/2013] [Accepted: 10/01/2013] [Indexed: 11/28/2022]
Abstract
Influenza A virus strains adopt different host specificities mainly depending on their hemagglutinin (HA) protein. Via HA, the virus binds sialic acid receptors of the host cell and, upon endocytic uptake, HA triggers fusion between the viral envelope bilayer and the endosomal membrane by a low pH-induced conformational change leading to the release of the viral genome into the host cell cytoplasm. Both functions are crucial for viral infection enabling the genesis of new progeny virus. Adaptation to different hosts in vitro was shown to require mutations within HA altering the receptor binding and/or fusion behavior of the respective virus strain. Human adapted influenza virus strains (H1N1, H3N2, H2N2) as well as recent avian influenza virus strains (H5, H7 and H9 subtypes) which gained the ability to infect humans mostly contained mutations in the receptor binding site (RBS) of HA enabling increased binding affinity of these viruses to human type (α-2,6 linked sialic acid) receptors. Thus, the receptor binding specificity seems to be the major requirement for successful adaptation to the human host; however, the RBS is not the only determinant of host specificity. Increased binding to a certain cell type does not always correlate with infection efficiency. Furthermore, viruses carrying mutations in the RBS often resulted in reduced viral fitness and were still unable to transmit between mammals. Recently, the pH stability of HA was reported to affect the transmissibility of influenza viruses. This review summarizes recent findings on the adaptation of influenza A viruses to the human host and related amino acid substitutions resulting in altered receptor binding specificity and/or modulated fusion pH of HA. Furthermore, the role of these properties (receptor specificity and pH stability of HA) for adaptation to and transmissibility in the human host is discussed. This article is part of a Special Issue entitled: Viral Membrane Proteins -- Channels for Cellular Networking.
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Affiliation(s)
- Caroline M Mair
- Group of Molecular Biophysics, Institute of Biology, Humboldt University Berlin, Invalidenstraße 42, 10115 Berlin, Germany
| | - Kai Ludwig
- Research center of Electron Microscopy, Institute of Chemistry and Biochemistry, Free University Berlin, Fabeckstraße 36a, 14195 Berlin, Germany
| | - Andreas Herrmann
- Group of Molecular Biophysics, Institute of Biology, Humboldt University Berlin, Invalidenstraße 42, 10115 Berlin, Germany.
| | - Christian Sieben
- Group of Molecular Biophysics, Institute of Biology, Humboldt University Berlin, Invalidenstraße 42, 10115 Berlin, Germany
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Xu S, Olenyuk BZ, Okamoto CT, Hamm-Alvarez SF. Targeting receptor-mediated endocytotic pathways with nanoparticles: rationale and advances. Adv Drug Deliv Rev 2013; 65:121-38. [PMID: 23026636 PMCID: PMC3565049 DOI: 10.1016/j.addr.2012.09.041] [Citation(s) in RCA: 298] [Impact Index Per Article: 27.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Revised: 09/13/2012] [Accepted: 09/20/2012] [Indexed: 12/22/2022]
Abstract
Targeting of drugs and their carrier systems by using receptor-mediated endocytotic pathways was in its nascent stages 25 years ago. In the intervening years, an explosion of knowledge focused on design and synthesis of nanoparticulate delivery systems as well as elucidation of the cellular complexity of what was previously-termed receptor-mediated endocytosis has now created a situation when it has become possible to design and test the feasibility of delivery of highly specific nanoparticle drug carriers to specific cells and tissue. This review outlines the mechanisms governing the major modes of receptor-mediated endocytosis used in drug delivery and highlights recent approaches using these as targets for in vivo drug delivery of nanoparticles. The review also discusses some of the inherent complexity associated with the simple shift from a ligand-drug conjugate versus a ligand-nanoparticle conjugate, in terms of ligand valency and its relationship to the mode of receptor-mediated internalization.
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Affiliation(s)
- Shi Xu
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA, USA 90033
| | - Bogdan Z. Olenyuk
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA, USA 90033
| | - Curtis T. Okamoto
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA, USA 90033
| | - Sarah F. Hamm-Alvarez
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA, USA 90033
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35
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Structural changes in Influenza virus at low pH characterized by cryo-electron tomography. J Virol 2012; 86:2919-29. [PMID: 22258245 DOI: 10.1128/jvi.06698-11] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Influenza virus enters host cells by endocytosis. The low pH of endosomes triggers conformational changes in hemagglutinin (HA) that mediate fusion of the viral and endosomal membranes. We have used cryo-electron tomography to visualize influenza A virus at pH 4.9, a condition known to induce fusogenicity. After 30 min, when all virions are in the postfusion state, dramatic changes in morphology are apparent: elongated particles are no longer observed, larger particles representing fused virions appear, the HA spikes become conspicuously disorganized, a layer of M1 matrix protein is no longer resolved on most virions, and the ribonucleoprotein complexes (RNPs) coagulate on the interior surface of the virion. To probe for intermediate states, preparations were imaged after 5 min at pH 4.9. These virions could be classified according to their glycoprotein arrays (organized or disorganized) and whether or not they have a resolved M1 layer. Employing subtomogram averaging, we found, in addition to the neutral-pH state of HA, two intermediate conformations that appear to reflect an outwards movement of the fusion peptide and rearrangement of the HA1 subunits, respectively. These changes are reversible. The tomograms also document pH-induced changes affecting the M1 layer that appear to render the envelope more pliable and hence conducive to fusion. However, it appears desirable for productive infection that fusion should proceed before the RNPs become coagulated with matrix protein, as eventually happens at low pH.
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36
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Lee KK, Pessi A, Gui L, Santoprete A, Talekar A, Moscona A, Porotto M. Capturing a fusion intermediate of influenza hemagglutinin with a cholesterol-conjugated peptide, a new antiviral strategy for influenza virus. J Biol Chem 2011; 286:42141-42149. [PMID: 21994935 DOI: 10.1074/jbc.m111.254243] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
We previously described fusion-inhibitory peptides that are targeted to the cell membrane by cholesterol conjugation and potently inhibit enveloped viruses that fuse at the cell surface, including HIV, parainfluenza, and henipaviruses. However, for viruses that fuse inside of intracellular compartments, fusion-inhibitory peptides have exhibited very low antiviral activity. We propose that for these viruses, too, membrane targeting via cholesterol conjugation may yield potent compounds. Here we compare the activity of fusion-inhibitory peptides derived from the influenza hemagglutinin (HA) and show that although the unconjugated peptides are inactive, the cholesterol-conjugated compounds are effective inhibitors of infectivity and membrane fusion. We hypothesize that the cholesterol moiety, by localizing the peptides to the target cell membrane, allows the peptides to follow the virus to the intracellular site of fusion. The cholesterol-conjugated peptides trap HA in a transient intermediate state after fusion is triggered but before completion of the refolding steps that drive the merging of the viral and cellular membranes. These results provide proof of concept for an antiviral strategy that is applicable to intracellularly fusing viruses, including known and emerging viral pathogens.
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Affiliation(s)
- Kelly K Lee
- Department of Medicinal Chemistry and Biomolecular Structure and Design Program, University of Washington, Seattle, Washington 98195.
| | - Antonello Pessi
- PeptiPharma, Via dei Castelli Romani 22, 00040 Pomezia, Rome, Italy
| | - Long Gui
- Department of Medicinal Chemistry and Biomolecular Structure and Design Program, University of Washington, Seattle, Washington 98195
| | - Alessia Santoprete
- Departments of Pediatrics and of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 10021
| | - Aparna Talekar
- Departments of Pediatrics and of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 10021
| | - Anne Moscona
- Departments of Pediatrics and of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 10021
| | - Matteo Porotto
- Departments of Pediatrics and of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 10021.
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Structural characterization of an early fusion intermediate of influenza virus hemagglutinin. J Virol 2011; 85:5172-82. [PMID: 21367895 DOI: 10.1128/jvi.02430-10] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The hemagglutinin (HA) envelope protein of influenza virus mediates viral entry through membrane fusion in the acidic environment of the endosome. Crystal structures of HA in pre- and postfusion states have laid the foundation for proposals for a general fusion mechanism for viral envelope proteins. The large-scale conformational rearrangement of HA at low pH is triggered by a loop-to-helix transition of an interhelical loop (B loop) within the fusion domain and is often referred to as the "spring-loaded" mechanism. Although the receptor-binding HA1 subunit is believed to act as a "clamp" to keep the B loop in its metastable prefusion state at neutral pH, the "pH sensors" that are responsible for the clamp release and the ensuing structural transitions have remained elusive. Here we identify a mutation in the HA2 fusion domain from the influenza virus H2 subtype that stabilizes the HA trimer in a prefusion-like state at and below fusogenic pH. Crystal structures of this putative early intermediate state reveal reorganization of ionic interactions at the HA1-HA2 interface at acidic pH and deformation of the HA1 membrane-distal domain. Along with neutralization of glutamate residues on the B loop, these changes cause a rotation of the B loop and solvent exposure of conserved phenylalanines, which are key residues at the trimer interface of the postfusion structure. Thus, our study reveals the possible initial structural event that leads to release of the B loop from its prefusion conformation, which is aided by unexpected structural changes within the membrane-distal HA1 domain at low pH.
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Shaw BF, Arthanari H, Narovlyansky M, Durazo A, Frueh DP, Pollastri MP, Lee A, Bilgicer B, Gygi SP, Wagner G, Whitesides GM. Neutralizing positive charges at the surface of a protein lowers its rate of amide hydrogen exchange without altering its structure or increasing its thermostability. J Am Chem Soc 2010; 132:17411-25. [PMID: 21090618 DOI: 10.1021/ja9067035] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
This paper combines two techniques--mass spectrometry and protein charge ladders--to examine the relationship between the surface charge and hydrophobicity of a representative globular protein (bovine carbonic anhydrase II; BCA II) and its rate of amide hydrogen-deuterium (H/D) exchange. Mass spectrometric analysis indicated that the sequential acetylation of surface lysine-ε-NH3(+) groups--a type of modification that increases the net negative charge and hydrophobicity of the surface of BCA II without affecting its secondary or tertiary structure--resulted in a linear decrease in the aggregate rate of amide H/D exchange at pD 7.4, 15 °C. According to analysis with MS, the acetylation of each additional lysine generated between 1.4 and 0.9 additional hydrogens that are protected from H/D exchange during the 2 h exchange experiment at 15 °C, pD 7.4. NMR spectroscopy demonstrated that none of the hydrogen atoms which became protected upon acetylation were located on the side chain of the acetylated lysine residues (i.e., lys-ε-NHCOCH3) but were instead located on amide NHCO moieties in the backbone. The decrease in rate of exchange associated with acetylation paralleled a decrease in thermostability: the most slowly exchanging rungs of the charge ladder were the least thermostable (as measured by differential scanning calorimetry). This observation--that faster rates of exchange are associated with slower rates of denaturation--is contrary to the usual assumptions in protein chemistry. The fact that the rates of H/D exchange were similar for perbutyrated BCA II (e.g., [lys-ε-NHCO(CH2)2CH3]18) and peracetylated BCA II (e.g., [lys-ε-NHCOCH3]18) suggests that the electrostatic charge is more important than the hydrophobicity of surface groups in determining the rate of H/D exchange. These electrostatic effects on the kinetics of H/D exchange could complicate (or aid) the interpretation of experiments in which H/D exchange methods are used to probe the structural effects of non-isoelectric perturbations to proteins (i.e., phosphorylation, acetylation, or the binding of the protein to an oligonucleotide or to another charged ligand or protein).
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Affiliation(s)
- Bryan F Shaw
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
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Jeong EK, Sung HM, Kim IS. Inactivation and removal of influenza A virus H1N1 during the manufacture of plasma derivatives. Biologicals 2010; 38:652-7. [DOI: 10.1016/j.biologicals.2010.07.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Revised: 07/23/2010] [Accepted: 07/27/2010] [Indexed: 12/01/2022] Open
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Abstract
Membrane fusion is an essential step during entry of enveloped viruses into cells. Conventional fusion assays are generally limited to observation of ensembles of multiple fusion events, confounding more detailed analysis of the sequence of the molecular steps involved. We have developed an in vitro, two-color fluorescence assay to monitor kinetics of single virus particles fusing with a target bilayer on an essentially fluid support. Analysis of lipid- and content-mixing trajectories on a particle-by-particle basis provides evidence for multiple, long-lived kinetic intermediates leading to hemifusion, followed by a single, rate-limiting step to pore formation. We interpret the series of intermediates preceding hemifusion as a result of the requirement that multiple copies of the trimeric hemagglutinin fusion protein be activated to initiate the fusion process.
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41
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Zhukovsky MA, Markovic I, Bailey AL. Influence of calcium on lipid mixing mediated by influenza hemagglutinin. Arch Biochem Biophys 2007; 465:101-8. [PMID: 17585869 PMCID: PMC2025700 DOI: 10.1016/j.abb.2007.05.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2007] [Revised: 04/30/2007] [Accepted: 05/01/2007] [Indexed: 11/22/2022]
Abstract
We studied the influence of calcium on lipid mixing mediated by influenza hemagglutinin (HA). Lipid mixing between HA-expressing cells and liposomes containing disialoganglioside, influenza virus receptor, was studied at 37 degrees C and neutral pH after a low-pH pulse at 4 degrees C. With DSPC/cholesterol liposomes, calcium present after raising the temperature significantly promoted lipid mixing only when it was triggered by a short low-pH application. In case of DOPC/cholesterol liposomes, calcium promotion was observed regardless of the duration of the low-pH pulse. Calcium present during a short, but not long, low-pH application to HA-expressing cells with bound DSPC/cholesterol liposomes at 4 degrees C inhibited subsequent lipid mixing. We hypothesize that calcium influences lipid mixing because it binds to a vestigial esterase domain of hemagglutinin or causes expulsion of the fusion peptide from an electronegative cavity. We suggest that calcium promotes the transition from early and reversible conformation(s) of low pH-activated HA towards an irreversible conformation that underlies both HA-mediated lipid mixing and HA inactivation.
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Affiliation(s)
- Mikhail A Zhukovsky
- Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
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Brown OJ, Lopez SA, Fuller AO, Goodson T. Formation and reversible dissociation of coiled coil of peptide to the C-terminus of the HSV B5 protein: a time-resolved spectroscopic analysis. Biophys J 2007; 93:1068-78. [PMID: 17496024 PMCID: PMC1913165 DOI: 10.1529/biophysj.106.100958] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2006] [Accepted: 04/09/2007] [Indexed: 11/18/2022] Open
Abstract
An understanding of the molecular mechanisms of the newly characterized herpes simplex virus (HSV) B5 protein is important to further elucidate the HSV cell entry and infection. The synthetic peptide of B5 (wtB5) was functionalized with the nonlinear optical chromophore cascade yellow and its molecular dynamics was probed at physiological and endosomal pH (pH 7.4 and 5.5, respectively). Steady-state CD spectroscopy was utilized to characterize the peptides at different pH. These spectra showed structural changes in the peptide with time measured over several days. Nonlinear optical measurements were carried out to probe the interactions and local environment of the labeled peptide, and the increase in the two-photon cross section of this system suggests an increase in chromophore-peptide interactions. Time-resolved fluorescence upconversion measurements reflected changes in the hydrophilic and hydrophobic local environments of the labeled peptide-chromophore system. Ultrafast depolarization measurements gave rotational correlation times indicative of a reversible change in the size of the peptide. The time-resolved results provide compelling evidence of a reversible dissociation of the coiled coils of the wtB5 peptide. This process was found to be pH-insensitive. The data from this unique combination of techniques provide an initial step to understanding the molecular dynamics of B5 and a framework for the development of novel imaging methods based on two-photon emission, as well as new therapeutics for HSV.
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Affiliation(s)
- Ordel J Brown
- Department of Chemistry, University of Michigan, USA
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43
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Shiryaev SA, Remacle AG, Ratnikov BI, Nelson NA, Savinov AY, Wei G, Bottini M, Rega MF, Parent A, Desjardins R, Fugere M, Day R, Sabet M, Pellecchia M, Liddington RC, Smith JW, Mustelin T, Guiney DG, Lebl M, Strongin AY. Targeting host cell furin proprotein convertases as a therapeutic strategy against bacterial toxins and viral pathogens. J Biol Chem 2007; 282:20847-53. [PMID: 17537721 DOI: 10.1074/jbc.m703847200] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Pathogens or their toxins, including influenza virus, Pseudomonas, and anthrax toxins, require processing by host proprotein convertases (PCs) to enter host cells and to cause disease. Conversely, inhibiting PCs is likely to protect host cells from multiple furin-dependent, but otherwise unrelated, pathogens. To determine if this concept is correct, we designed specific nanomolar inhibitors of PCs modeled from the extended cleavage motif TPQRERRRKKR downward arrowGL of the avian influenza H5N1 hemagglutinin. We then confirmed the efficacy of the inhibitory peptides in vitro against the fluorescent peptide, anthrax protective antigen (PA83), and influenza hemagglutinin substrates and also in mice in vivo against two unrelated toxins, anthrax and Pseudomonas exotoxin. Peptides with Phe/Tyr at P1' were more selective for furin. Peptides with P1' Thr were potent against multiple PCs. Our strategy of basing the peptide sequence on a furin cleavage motif known for an avian flu virus shows the power of starting inhibitor design with a known substrate. Our results confirm that inhibiting furin-like PCs protects the host from the distinct furin-dependent infections and lay a foundation for novel, host cell-focused therapies against acute diseases.
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Affiliation(s)
- Sergey A Shiryaev
- Burnham Institute for Medical Research, La Jolla, California 92037, USA
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44
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Kreil TR, Unger U, Orth SM, Petutschnig G, Kistner O, Poelsler G, Berting A. H5N1 influenza virus and the safety of plasma products. Transfusion 2007; 47:452-9. [PMID: 17319825 DOI: 10.1111/j.1537-2995.2007.01135.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND The ever-increasing number of human H5N1 influenza virus infections may enable these viruses to acquire the ability to spread effectively among humans and potentially to cause a pandemic. Recently, more systemic virus dissemination was reported during H5N1 virus infection of humans, resulting in significant virus concentrations also in the blood. The observation has raised concerns about the safety of labile blood products for transfusion and consequentially also for plasma derivatives. To confirm the safety margins of plasma products, dedicated virus inactivation processes used during their production were investigated for their effectiveness in inactivating this virus of recent concern. STUDY DESIGN AND METHODS Virus inactivation by steps commonly used during the manufacture of plasma derivatives, such as pasteurization for human albumin, solvent/detergent treatment for intravenous immunoglobulin (IVIG), vapor heating for factor VIII inhibitor bypassing activity, and incubation at low pH for IVIG, were investigated with a reassortant strain of H5N1 influenza virus. RESULTS The results show that H5N1 influenza behaves as expected for lipid-enveloped viruses; that is, the virus is effectively inactivated by all the commonly used virus inactivation procedures tested. CONCLUSION The safety margins of plasma derivatives against the theoretical transmission of H5N1 influenza virus are very substantial.
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Affiliation(s)
- T R Kreil
- Global Pathogen Safety and R&D Vaccines, Baxter BioScience, Vienna, Austria.
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45
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Korte T, Ludwig K, Huang Q, Rachakonda PS, Herrmann A. Conformational change of influenza virus hemagglutinin is sensitive to ionic concentration. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 36:327-35. [PMID: 17211621 DOI: 10.1007/s00249-006-0116-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2006] [Revised: 11/03/2006] [Accepted: 11/17/2006] [Indexed: 11/29/2022]
Abstract
The homotrimeric spike glycoprotein hemagglutinin (HA) of influenza virus undergoes a low pH-mediated conformational change which mediates the fusion of the viral envelope with the target membrane. Previous approaches predict that the interplay of electrostatic interactions between and within HA subunits, HA 1 and HA2, are essential for the metastability of the HA ectodomain. Here, we show that suspension media of low ionic concentration promote fusion of fluorescent labelled influenza virus X31 with erythrocyte ghosts and with ganglioside containing liposomes. By measuring the low pH mediated inactivation of the fusion competence of HA and the Proteinase K sensitivity of low pH incubated HA we show that the conformational change is promoted by low ionic concentration. We surmise that electrostatic attraction within the HA ectodomain is weakened by lowering the ionic concentration facilitating the conformational change at low pH.
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Affiliation(s)
- Thomas Korte
- Institute of Biology, Molecular Biophysics, Humboldt University, Berlin 10115, Germany
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46
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Lee JH, Goulian M, Boder ET. Autocatalytic Activation of Influenza Hemagglutinin. J Mol Biol 2006; 364:275-82. [PMID: 17011576 DOI: 10.1016/j.jmb.2006.09.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2006] [Revised: 09/05/2006] [Accepted: 09/05/2006] [Indexed: 11/25/2022]
Abstract
Enveloped viruses contain surface proteins that mediate fusion between the viral and target cell membranes following an activating stimulus. Acidic pH induces the influenza virus fusion protein hemagglutinin (HA) via irreversible refolding of a trimeric conformational state leading to exposure of hydrophobic fusion peptides on each trimer subunit. Herein, we show that cells expressing fowl plague virus HA demonstrate discrete switching behavior with respect to the HA conformational change. Partially activated states do not exist at the scale of the cell, activation of HA leads to aggregation of cell surface trimers, and newly synthesized HA refold spontaneously in the presence of previously activated HA. These observations imply a feedback mechanism involving self-catalyzed refolding of HA and thus suggest a mechanism similar to the autocatalytic refolding and aggregation of prions.
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Affiliation(s)
- Jeong H Lee
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, 220 South 33rd Street, Philadelphia, PA 19104, USA
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47
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Zhukovsky MA, Leikina E, Markovic I, Bailey AL, Chernomordik LV. Heterogeneity of early intermediates in cell-liposome fusion mediated by influenza hemagglutinin. Biophys J 2006; 91:3349-58. [PMID: 16905609 PMCID: PMC1614502 DOI: 10.1529/biophysj.106.088005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
To explore early intermediates in membrane fusion mediated by influenza virus hemagglutinin (HA) and their dependence on the composition of the target membrane, we studied lipid mixing between HA-expressing cells and liposomes containing phosphatidylcholine (PC) with different hydrocarbon chains. For all tested compositions, our results indicate the existence of at least two types of intermediates, which differ in their lifetimes. The composition of the target membrane affects the stability of fusion intermediates at a stage before lipid mixing. For less fusogenic distearoyl PC-containing liposomes at 4 degrees C, some of the intermediates inactivate, and no intermediates advance to lipid mixing. Fusion intermediates that formed for the more fusogenic dioleoyl PC-containing liposomes did not inactivate and even yielded partial lipid mixing at 4 degrees C. Thus, a more fusogenic target membrane effectively blocks nonproductive release of the conformational energy of HA. Even for the same liposome composition, HA forms two types of fusion intermediates, dissimilar in their stability and propensity to fuse. This diversity of fusion intermediates emphasizes the importance of local membrane composition and local protein concentration in fusion of heterogeneous biological membranes.
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Affiliation(s)
- Mikhail A Zhukovsky
- Laboratory of Cellular and Molecular Biophysics, Section on Membrane Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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48
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Chang DK, Cheng SF. pH-dependence of intermediate steps of membrane fusion induced by the influenza fusion peptide. Biochem J 2006; 396:557-63. [PMID: 16519629 PMCID: PMC1482821 DOI: 10.1042/bj20051920] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Membrane fusion mediated by the influenza-virus fusion protein is activated by low pH via a cascade of reactions. Some processes among them are irreversible, such as helix hairpin formation of the ectodomain, whereas others are reversible, such as exposure of the fusion peptide. Using this property, we attempted to dissect, in temporal order, different stages of the fusion reaction involving the fusion peptide by an acidic-neutral-acidic pH cycle. The fluorescence-quenching data indicated that both insertion depth and self-assembly are pH-reversible. In addition, lipid mixing assay was demonstrated to be arrested by neutral pH. By contrast, membrane leakage was shown to be irreversible with respect to pH. Our results, along with those from other studies on the pH-dependence of membrane fusion, are used to build a model for the virus-mediated fusion event from the perspective of pH-reversibility.
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Affiliation(s)
- Ding-Kwo Chang
- Institute of Chemistry, Academia Sinica, Taipei, Taiwan 115, Republic of China.
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49
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Wallin M, Löving R, Ekström M, Li K, Garoff H. Kinetic analyses of the surface-transmembrane disulfide bond isomerization-controlled fusion activation pathway in Moloney murine leukemia virus. J Virol 2006; 79:13856-64. [PMID: 16254321 PMCID: PMC1280236 DOI: 10.1128/jvi.79.22.13856-13864.2005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The surface (SU) and transmembrane (TM) subunits of Moloney murine leukemia virus (Mo-MLV) Env are disulfide linked. The linking cysteine in SU is part of a conserved CXXC motif in which the other cysteine carries a free thiol. Recently, we showed that receptor binding activates its free thiol to isomerize the intersubunit disulfide bond into a disulfide within the motif instead (M. Wallin, M. Ekström and H. Garoff, EMBO J. 23:54-65, 2004). This facilitated SU dissociation and activation of TM for membrane fusion. The evidence was mainly based on the finding that alkylation of the CXXC-thiol prevented isomerization. This arrested membrane fusion, but the activity could be rescued by cleaving the intersubunit disulfide bond with dithiothreitol (DTT). Here, we demonstrate directly that receptor binding causes SU-TM disulfide bond isomerization in a subfraction of the viral Envs. The kinetics of the isomerization followed that of virus-cell membrane fusion. Arresting the fusion with lysophosphatidylcholine did not arrest isomerization, suggesting that isomerization precedes the hemifusion stage of fusion. Our earlier finding that native Env was not possible to alkylate but required isomerization induction by receptor binding intimated that alkylation trapped an intermediate form of Env. To further clarify this possibility, we analyzed the kinetics by which the alkylation-sensitive Env was generated during fusion. We found that it followed the fusion kinetics. In contrast, the release of fusion from alkylated, isomerization-blocked virus by DTT reduction of the SU-TM disulfide bond was much faster. These results suggest that the alkylation-sensitive form of Env is a true intermediate in the fusion activation pathway of Env.
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Affiliation(s)
- Michael Wallin
- Department of Biosciences at Novum, Karolinska Institute, S-141 57 Huddinge, Sweden
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50
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Sun X, Whittaker GR. Entry of influenza virus. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2006; 790:72-82. [PMID: 23884586 DOI: 10.1007/978-1-4614-7651-1_4] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
As a major pathogen of human and certain animal species, influenza virus causes wide spread and potentially devastating disease. To initiate infection, the virus first binds to cellular receptors comprising either -(2,3 ) or -(2,6) linked sialic acid. Recent advances in our understanding of the influenza virus receptor and viral host species involved have shed light on the molecular mechanism of how influenza virus transmits across species and adapts to a new host. Following receptor binding, influenza viruses are internalized through multiple endocytic pathways, including both clathrin- and non-clathrin-dependent routes, which have recently been visualized at single viral particle level. The viral envelope then fuses with the endosomal membrane in a low pH-dependent manner and the viral genome is released into the cytosol, followed by further transport to the nucleus where genome replication occurs.
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Affiliation(s)
- Xiangjie Sun
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY, USA
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