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Crampon E, Covernton E, Vaney MC, Dellarole M, Sommer S, Sharma A, Haouz A, England P, Lepault J, Duquerroy S, Rey FA, Barba-Spaeth G. New insight into flavivirus maturation from structure/function studies of the yellow fever virus envelope protein complex. mBio 2023; 14:e0070623. [PMID: 37607061 PMCID: PMC10653854 DOI: 10.1128/mbio.00706-23] [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: 03/19/2023] [Accepted: 06/16/2023] [Indexed: 08/24/2023] Open
Abstract
IMPORTANCE All enveloped viruses enter cells by fusing their envelope with a target cell membrane while avoiding premature fusion with membranes of the producer cell-the latter being particularly important for viruses that bud at internal membranes. Flaviviruses bud in the endoplasmic reticulum, are transported through the TGN to reach the external milieu, and enter other cells via receptor-mediated endocytosis. The trigger for membrane fusion is the acidic environment of early endosomes, which has a similar pH to the TGN of the producer cell. The viral particles therefore become activated to react to mildly acidic pH only after their release into the neutral pH extracellular environment. Our study shows that for yellow fever virus (YFV), the mechanism of activation involves actively knocking out the fusion brake (protein pr) through a localized conformational change of the envelope protein upon exposure to the neutral pH external environment. Our study has important implications for understanding the molecular mechanism of flavivirus fusion activation in general and points to an alternative way of interfering with this process as an antiviral treatment.
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Affiliation(s)
- E. Crampon
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
| | - E. Covernton
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
| | - M. C. Vaney
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
| | - M. Dellarole
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
| | - S. Sommer
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
| | - A. Sharma
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
| | - A. Haouz
- Institut Pasteur, Université Paris Cité, CNRS UMR 3528, Plateforme de Cristallographie-C2RT, Paris, France
| | - P. England
- Institut Pasteur, Université Paris Cité, CNRS UMR 3528, Plateforme de Biophysique Moléculaire-C2RT, Paris, France
| | - J. Lepault
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Saclay, Gif-sur-Yvette, France
| | - S. Duquerroy
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
- Université Paris-Saclay, Faculté des Sciences, Orsay, France
| | - F. A. Rey
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
| | - G. Barba-Spaeth
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
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2
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Bignon E, Dumont E, Monari A. Molecular Basis of the pH-Controlled Maturation of the Tick-Borne Encephalitis Flavivirus. J Phys Chem Lett 2023; 14:1977-1982. [PMID: 36790164 DOI: 10.1021/acs.jpclett.2c03551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Flaviviruses are enveloped viruses causing high public concerns. Their maturation spans several cellular compartments having different pH. Thus, complex control mechanisms are in place to avoid premature maturation. Here we report the dynamical behavior at neutral and acidic pH of the precursor of the membrane fusion protein E of tick-borne encephalitis, showing the different stabilizations of the E dimer and the role played by the small fusion-assisting protomer (pr). The comprehension, at atomic resolution, of the fine regulation of viral maturation will be fundamental to the development of efficient strategies against emerging viral threats.
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Affiliation(s)
- Emmanuelle Bignon
- Université de Lorraine and CNRS, UMR 7019 LPCT, F-5400, Nancy, France
| | - Elise Dumont
- Université Côte d'Azur, Institut de Chimie de Nice, UMR 7272, Parc Valrose, 28 avenue Valrose, F-06108, Nice, France
- Institut Universitaire de France, 5 rue Descartes, F-75005, Paris, France
| | - Antonio Monari
- Université Paris Cité and CNRS, ITODYS, F-75006, Paris, France
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3
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Vaney MC, Dellarole M, Duquerroy S, Medits I, Tsouchnikas G, Rouvinski A, England P, Stiasny K, Heinz FX, Rey FA. Evolution and activation mechanism of the flavivirus class II membrane-fusion machinery. Nat Commun 2022; 13:3718. [PMID: 35764616 PMCID: PMC9239988 DOI: 10.1038/s41467-022-31111-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Accepted: 06/03/2022] [Indexed: 11/08/2022] Open
Abstract
The flavivirus envelope glycoproteins prM and E drive the assembly of icosahedral, spiky immature particles that bud across the membrane of the endoplasmic reticulum. Maturation into infectious virions in the trans-Golgi network involves an acid-pH-driven rearrangement into smooth particles made of (prM/E)2 dimers exposing a furin site for prM cleavage into "pr" and "M". Here we show that the prM "pr" moiety derives from an HSP40 cellular chaperonin. Furthermore, the X-ray structure of the tick-borne encephalitis virus (pr/E)2 dimer at acidic pH reveals the E 150-loop as a hinged-lid that opens at low pH to expose a positively-charged pr-binding pocket at the E dimer interface, inducing (prM/E)2 dimer formation to generate smooth particles in the Golgi. Furin cleavage is followed by lid-closure upon deprotonation in the neutral-pH extracellular environment, expelling pr while the 150-loop takes the relay in fusion loop protection, thus revealing the elusive flavivirus mechanism of fusion activation.
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Affiliation(s)
- Marie-Christine Vaney
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
| | - Mariano Dellarole
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
- CIBION, CONICET, Buenos Aires, Argentina
| | - Stéphane Duquerroy
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
- Université Paris Saclay, Faculté des Sciences, Orsay, France
| | - Iris Medits
- Center for Virology, Medical University of Vienna, Vienna, Austria
| | - Georgios Tsouchnikas
- Center for Virology, Medical University of Vienna, Vienna, Austria
- HOOKIPA Pharma 19 Inc, Vienna, Austria
| | - Alexander Rouvinski
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France
- Department of Microbiology and Molecular Genetics, Institute for Medical Research Israel-Canada, The Kuvin Center for the Study of Infectious and Tropical Diseases, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Patrick England
- Institut Pasteur, Université Paris Cité, CNRS UMR 3528, Plateforme de Biophysique Moléculaire, Paris, France
| | - Karin Stiasny
- Center for Virology, Medical University of Vienna, Vienna, Austria.
| | - Franz X Heinz
- Center for Virology, Medical University of Vienna, Vienna, Austria.
| | - Félix A Rey
- Institut Pasteur, Université Paris Cité, CNRS UMR 3569, Unité de Virologie Structurale, Paris, France.
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4
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Mishra AK, Hellert J, Freitas N, Guardado-Calvo P, Haouz A, Fels JM, Maurer DP, Abelson DM, Bornholdt ZA, Walker LM, Chandran K, Cosset FL, McLellan JS, Rey FA. Structural basis of synergistic neutralization of Crimean-Congo hemorrhagic fever virus by human antibodies. Science 2022; 375:104-109. [PMID: 34793197 PMCID: PMC9771711 DOI: 10.1126/science.abl6502] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Crimean-Congo hemorrhagic fever virus (CCHFV) is the most widespread tick-borne zoonotic virus, with a 30% case fatality rate in humans. Structural information is lacking in regard to the CCHFV membrane fusion glycoprotein Gc—the main target of the host neutralizing antibody response—as well as antibody–mediated neutralization mechanisms. We describe the structure of prefusion Gc bound to the antigen-binding fragments (Fabs) of two neutralizing antibodies that display synergy when combined, as well as the structure of trimeric, postfusion Gc. The structures show the two Fabs acting in concert to block membrane fusion, with one targeting the fusion loops and the other blocking Gc trimer formation. The structures also revealed the neutralization mechanism of previously reported antibodies against CCHFV, providing the molecular underpinnings essential for developing CCHFV–specific medical countermeasures for epidemic preparedness.
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Affiliation(s)
- Akaash K. Mishra
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA 78712
| | - Jan Hellert
- Structural Virology Unit, Institut Pasteur, CNRS UMR 3569, 25-28 rue du Docteur Roux, Cedex 15, Paris, France 75724
| | - Natalia Freitas
- CIRI-Centre International de Recherche en Infectiologie, Univ Lyon, Université Claude Bernard Lyon 1, Inserm, U1111, CNRS, UMR5308, ENS Lyon, 46 allée d’Italie, Lyon, France 69007
| | - Pablo Guardado-Calvo
- Structural Virology Unit, Institut Pasteur, CNRS UMR 3569, 25-28 rue du Docteur Roux, Cedex 15, Paris, France 75724
| | - Ahmed Haouz
- Crystallography Platform C2RT, Institut Pasteur, CNRS UMR 3528, 25-28 rue du Docteur Roux, Cedex 15, Paris, France 75724
| | - J. Maximilian Fels
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA 10461
| | | | | | | | | | - Kartik Chandran
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA 10461
| | - François-Loïc Cosset
- CIRI-Centre International de Recherche en Infectiologie, Univ Lyon, Université Claude Bernard Lyon 1, Inserm, U1111, CNRS, UMR5308, ENS Lyon, 46 allée d’Italie, Lyon, France 69007
| | - Jason S. McLellan
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA 78712,Correspondence: (J.S.M.); (F.A.R)
| | - Felix A. Rey
- Structural Virology Unit, Institut Pasteur, CNRS UMR 3569, 25-28 rue du Docteur Roux, Cedex 15, Paris, France 75724,Correspondence: (J.S.M.); (F.A.R)
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5
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Williamson LE, Reeder KM, Bailey K, Tran MH, Roy V, Fouch ME, Kose N, Trivette A, Nargi RS, Winkler ES, Kim AS, Gainza C, Rodriguez J, Armstrong E, Sutton RE, Reidy J, Carnahan RH, McDonald WH, Schoeder CT, Klimstra WB, Davidson E, Doranz BJ, Alter G, Meiler J, Schey KL, Julander JG, Diamond MS, Crowe JE. Therapeutic alphavirus cross-reactive E1 human antibodies inhibit viral egress. Cell 2021; 184:4430-4446.e22. [PMID: 34416147 PMCID: PMC8418820 DOI: 10.1016/j.cell.2021.07.033] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 04/11/2021] [Accepted: 07/26/2021] [Indexed: 12/11/2022]
Abstract
Alphaviruses cause severe arthritogenic or encephalitic disease. The E1 structural glycoprotein is highly conserved in these viruses and mediates viral fusion with host cells. However, the role of antibody responses to the E1 protein in immunity is poorly understood. We isolated E1-specific human monoclonal antibodies (mAbs) with diverse patterns of recognition for alphaviruses (ranging from Eastern equine encephalitis virus [EEEV]-specific to alphavirus cross-reactive) from survivors of natural EEEV infection. Antibody binding patterns and epitope mapping experiments identified differences in E1 reactivity based on exposure of epitopes on the glycoprotein through pH-dependent mechanisms or presentation on the cell surface prior to virus egress. Therapeutic efficacy in vivo of these mAbs corresponded with potency of virus egress inhibition in vitro and did not require Fc-mediated effector functions for treatment against subcutaneous EEEV challenge. These studies reveal the molecular basis for broad and protective antibody responses to alphavirus E1 proteins.
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MESH Headings
- Alphavirus/immunology
- Animals
- Antibodies, Monoclonal/immunology
- Antibodies, Monoclonal/isolation & purification
- Antibodies, Neutralizing/immunology
- Antibodies, Viral/immunology
- Antigens, Viral/immunology
- Cell Line
- Chikungunya virus/immunology
- Cross Reactions/immunology
- Encephalitis Virus, Eastern Equine/immunology
- Encephalomyelitis, Equine/immunology
- Encephalomyelitis, Equine/virology
- Epitope Mapping
- Female
- Horses
- Humans
- Hydrogen-Ion Concentration
- Joints/pathology
- Male
- Mice, Inbred C57BL
- Models, Biological
- Protein Binding
- RNA, Viral/metabolism
- Receptors, Fc/metabolism
- Temperature
- Viral Proteins/immunology
- Virion/metabolism
- Virus Internalization
- Virus Release/physiology
- Mice
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Affiliation(s)
- Lauren E Williamson
- Department of Pathology, Microbiology and Immunology, Vanderbilt University, Nashville, TN 37232, USA; The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Kristen M Reeder
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Kevin Bailey
- Institute for Antiviral Research, Utah State University, Logan, UT 84335, USA
| | - Minh H Tran
- Chemical and Physical Biology Program, Vanderbilt University, Nashville, TN, USA; Center of Structural Biology, Vanderbilt University, Nashville, TN, USA; Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University, Nashville, TN, USA
| | - Vicky Roy
- Ragon Institute of MGH, MIT, and Harvard University, Cambridge, MA 02139, USA
| | | | - Nurgun Kose
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Andrew Trivette
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Rachel S Nargi
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Emma S Winkler
- Department of Medicine, Washington University, St. Louis, MO 63110, USA; Department of Pathology and Immunology, Washington University, St. Louis, MO 63110, USA
| | - Arthur S Kim
- Department of Medicine, Washington University, St. Louis, MO 63110, USA; Department of Pathology and Immunology, Washington University, St. Louis, MO 63110, USA
| | - Christopher Gainza
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Jessica Rodriguez
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Erica Armstrong
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Rachel E Sutton
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Joseph Reidy
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Robert H Carnahan
- The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - W Hayes McDonald
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University, Nashville, TN, USA
| | - Clara T Schoeder
- Center of Structural Biology, Vanderbilt University, Nashville, TN, USA; Department of Chemistry, Vanderbilt University, Nashville, TN, USA
| | - William B Klimstra
- The Center for Vaccine Research, University of Pittsburgh, Pittsburgh, PA 165261, USA; Department of Immunology, University of Pittsburgh, Pittsburgh, PA 165261, USA
| | | | | | - Galit Alter
- Ragon Institute of MGH, MIT, and Harvard University, Cambridge, MA 02139, USA
| | - Jens Meiler
- Center of Structural Biology, Vanderbilt University, Nashville, TN, USA; Department of Chemistry, Vanderbilt University, Nashville, TN, USA; Institute for Drug Discovery, Leipzig University Medical School, Leipzig, Germany
| | - Kevin L Schey
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University, Nashville, TN, USA
| | - Justin G Julander
- Institute for Antiviral Research, Utah State University, Logan, UT 84335, USA
| | - Michael S Diamond
- Department of Medicine, Washington University, St. Louis, MO 63110, USA; Department of Pathology and Immunology, Washington University, St. Louis, MO 63110, USA; Department of Molecular Microbiology, Washington University, St. Louis, MO 63110, USA
| | - James E Crowe
- Department of Pathology, Microbiology and Immunology, Vanderbilt University, Nashville, TN 37232, USA; Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232, USA; The Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
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6
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Kudlacek ST, Premkumar L, Metz SW, Tripathy A, Bobkov AA, Payne AM, Graham S, Brackbill JA, Miley MJ, de Silva AM, Kuhlman B. Physiological temperatures reduce dimerization of dengue and Zika virus recombinant envelope proteins. J Biol Chem 2018; 293:8922-8933. [PMID: 29678884 PMCID: PMC5995514 DOI: 10.1074/jbc.ra118.002658] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 04/13/2018] [Indexed: 01/01/2023] Open
Abstract
The spread of dengue (DENV) and Zika virus (ZIKV) is a major public health concern. The primary target of antibodies that neutralize DENV and ZIKV is the envelope (E) glycoprotein, and there is interest in using soluble recombinant E (sRecE) proteins as subunit vaccines. However, the most potent neutralizing antibodies against DENV and ZIKV recognize epitopes on the virion surface that span two or more E proteins. Therefore, to create effective DENV and ZIKV vaccines, presentation of these quaternary epitopes may be necessary. The sRecE proteins from DENV and ZIKV crystallize as native-like dimers, but studies in solution suggest that these dimers are marginally stable. To better understand the challenges associated with creating stable sRecE dimers, we characterized the thermostability of sRecE proteins from ZIKV and three DENV serotypes, DENV2-4. All four proteins irreversibly unfolded at moderate temperatures (46-53 °C). At 23 °C and low micromolar concentrations, DENV2 and ZIKV were primarily dimeric, and DENV3-4 were primarily monomeric, whereas at 37 °C, all four proteins were predominantly monomeric. We further show that the dissociation constant for DENV2 dimerization is very temperature-sensitive, ranging from <1 μm at 25 °C to 50 μm at 41 °C, due to a large exothermic enthalpy of binding of -79 kcal/mol. We also found that quaternary epitope antibody binding to DENV2-4 and ZIKV sRecE is reduced at 37 °C. Our observation of reduced sRecE dimerization at physiological temperature highlights the need for stabilizing the dimer as part of its development as a subunit vaccine.
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Affiliation(s)
- Stephan T Kudlacek
- From the Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599
| | - Lakshmanane Premkumar
- the Department of Microbiology and Immunology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599
| | - Stefan W Metz
- the Department of Microbiology and Immunology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599
| | - Ashutosh Tripathy
- From the Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599
| | - Andrey A Bobkov
- the Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037
| | - Alexander Matthew Payne
- From the Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599
| | - Stephen Graham
- the Department of Microbiology and Immunology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599
| | - James A Brackbill
- the Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, and
| | - Michael J Miley
- the Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, and
| | - Aravinda M de Silva
- the Department of Microbiology and Immunology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599
| | - Brian Kuhlman
- From the Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599,
- the Lineburger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
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7
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Covalently linked dengue virus envelope glycoprotein dimers reduce exposure of the immunodominant fusion loop epitope. Nat Commun 2017; 8:15411. [PMID: 28534525 PMCID: PMC5457521 DOI: 10.1038/ncomms15411] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Accepted: 03/23/2017] [Indexed: 12/22/2022] Open
Abstract
A problem in the search for an efficient vaccine against dengue virus is the immunodominance of the fusion loop epitope (FLE), a segment of the envelope protein E that is buried at the interface of the E dimers coating mature viral particles. Anti-FLE antibodies are broadly cross-reactive but poorly neutralizing, displaying a strong infection enhancing potential. FLE exposure takes place via dynamic ‘breathing' of E dimers at the virion surface. In contrast, antibodies targeting the E dimer epitope (EDE), readily exposed at the E dimer interface over the region of the conserved fusion loop, are very potent and broadly neutralizing. We here engineer E dimers locked by inter-subunit disulfide bonds, and show by X-ray crystallography and by binding to a panel of human antibodies that these engineered dimers do not expose the FLE, while retaining the EDE exposure. These locked dimers are strong immunogen candidates for a next-generation vaccine. The immunodominant epitope of dengue virus envelope protein (E) induces poorly neutralizing antibodies, which poses a problem for vaccine development. Here, the authors engineer covalently locked E dimers exposing an epitope that has been shown to induce potent and broadly neutralizing antibodies.
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8
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Fusion of mApple and Venus fluorescent proteins to the Sindbis virus E2 protein leads to different cell-binding properties. Virus Res 2013; 177:138-46. [PMID: 23916968 DOI: 10.1016/j.virusres.2013.07.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Revised: 07/12/2013] [Accepted: 07/17/2013] [Indexed: 11/23/2022]
Abstract
Fluorescent proteins (FPs) are widely used in real-time single virus particle studies to visualize, track and quantify the spatial and temporal parameters of viral pathways. However, potential functional differences between the wild type and the FP-tagged virus may specifically affect particular stages in the virus life-cycle. In this work, we genetically modified the E2 spike protein of Sindbis virus (SINV) with two FPs. We inserted mApple, a red FP, or Venus, a yellow FP, at the N-terminus of the E2 protein of SINV to make SINV-Apple and SINV-Venus. Our results indicate that SINV-Apple and SINV-Venus have similar levels of infectivity and are morphologically similar to SINV-wild-type by negative stain transmission electron microscopy. Both mutants are highly fluorescent and have excellent single-particle tracking properties. However, despite these similarities, when measuring cell entry at the single-particle level, we found that SINV-Apple and SINV-Venus are different in their interaction with the cell surface and FPs are not always interchangeable. We went on to determine that the FP changes the net surface charge on the virus particles, the folding of the spike proteins, and the conformation of the spikes on the virus particle surface, ultimately leading to different cell-binding properties between SINV-Apple and SINV-Venus. Our results are consistent with recent findings that FPs may alter the biological and cellular localization properties of bacterial proteins to which they are fused.
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9
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Abstract
The study of enveloped animal viruses has greatly advanced our understanding of the general properties of membrane fusion and of the specific pathways that viruses use to infect the host cell. The membrane fusion proteins of the alphaviruses and flaviviruses have many similarities in structure and function. As reviewed here, alphaviruses use receptor-mediated endocytic uptake and low pH-triggered membrane fusion to deliver their RNA genomes into the cytoplasm. Recent advances in understanding the biochemistry and structure of the alphavirus membrane fusion protein provide a clearer picture of this fusion reaction, including the protein’s conformational changes during fusion and the identification of key domains. These insights into the alphavirus fusion mechanism suggest new areas for experimental investigation and potential inhibitor strategies for anti-viral therapy.
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Affiliation(s)
- Margaret Kielian
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +1-718-430-3638; Fax: +1-718-430-8574
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10
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Jose J, Snyder JE, Kuhn RJ. A structural and functional perspective of alphavirus replication and assembly. Future Microbiol 2009; 4:837-56. [PMID: 19722838 DOI: 10.2217/fmb.09.59] [Citation(s) in RCA: 234] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Alphaviruses are small, spherical, enveloped, positive-sense ssRNA viruses responsible for a considerable number of human and animal diseases. Alphavirus members include Chikungunya virus, Sindbis virus, Semliki Forest virus, the western, eastern and Venezuelan equine encephalitis viruses, and the Ross River virus. Alphaviruses can cause arthritic diseases and encephalitis in humans and animals and continue to be a worldwide threat. The viruses are transmitted by blood-sucking arthropods, and replicate in both arthropod and vertebrate hosts. Alphaviruses form spherical particles (65-70 nm in diameter) with icosahedral symmetry and a triangulation number of four. The icosahedral structures of alphaviruses have been defined to very high resolutions by cryo-electron microscopy and crystallographic studies. In this review, we summarize the major events in alphavirus infection: entry, replication, assembly and budding. We focus on data acquired from structural and functional studies of the alphaviruses. These structural and functional data provide a broader perspective of the virus lifecycle and structure, and allow additional insight into these important viruses.
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Affiliation(s)
- Joyce Jose
- Department of Biological Sciences, Bindley Bioscience Center, Lilly Hall of Life Sciences, 915 West State St., Purdue University, West Lafayette, IN 47907, USA.
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11
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Non-hemagglutinating flaviviruses: molecular mechanisms for the emergence of new strains via adaptation to European ticks. PLoS One 2009; 4:e7295. [PMID: 19802385 PMCID: PMC2750751 DOI: 10.1371/journal.pone.0007295] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2009] [Accepted: 09/08/2009] [Indexed: 12/31/2022] Open
Abstract
Tick-borne encephalitis virus (TBEV) causes human epidemics across Eurasia. Clinical manifestations range from inapparent infections and fevers to fatal encephalitis but the factors that determine disease severity are currently undefined. TBEV is characteristically a hemagglutinating (HA) virus; the ability to agglutinate erythrocytes tentatively reflects virion receptor/fusion activity. However, for the past few years many atypical HA-deficient strains have been isolated from patients and also from the natural European host tick, Ixodes persulcatus. By analysing the sequences of HA-deficient strains we have identified 3 unique amino acid substitutions (D67G, E122G or D277A) in the envelope protein, each of which increases the net charge and hydrophobicity of the virion surface. Therefore, we genetically engineered virus mutants each containing one of these 3 substitutions; they all exhibited HA-deficiency. Unexpectedly, each genetically modified non-HA virus demonstrated increased TBEV reproduction in feeding Ixodes ricinus, not the recognised tick host for these strains. Moreover, virus transmission efficiency between infected and uninfected ticks co-feeding on mice was also intensified by each substitution. Retrospectively, the mutation D67G was identified in viruses isolated from patients with encephalitis. We propose that the emergence of atypical Siberian HA-deficient TBEV strains in Europe is linked to their molecular adaptation to local ticks. This process appears to be driven by the selection of single mutations that change the virion surface thus enhancing receptor/fusion function essential for TBEV entry into the unfamiliar tick species. As the consequence of this adaptive mutagenesis, some of these mutations also appear to enhance the ability of TBEV to cross the human blood-brain barrier, a likely explanation for fatal encephalitis. Future research will reveal if these emerging Siberian TBEV strains continue to disperse westwards across Europe by adaptation to the indigenous tick species and if they are associated with severe forms of TBE.
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Hernandez R, Paredes A. Sindbis virus as a model for studies of conformational changes in a metastable virus and the role of conformational changes in in vitro antibody neutralisation. Rev Med Virol 2009; 19:257-72. [DOI: 10.1002/rmv.619] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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13
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Abstract
Enveloped animal viruses fuse their membrane with a host cell membrane, thus delivering the virus genetic material into the cytoplasm and initiating infection. This critical membrane fusion reaction is mediated by a virus transmembrane protein known as the fusion protein, which inserts its hydrophobic fusion peptide into the cell membrane and refolds to drive the fusion reaction. This review describes recent advances in our understanding of the structure and function of the class II fusion proteins of the alphaviruses and flaviviruses. Inhibition of the fusion protein refolding reaction confirms its importance in fusion and suggests new antiviral strategies for these medically important viruses.
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Affiliation(s)
- Margaret Kielian
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA.
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Roussel A, Lescar J, Vaney MC, Wengler G, Wengler G, Rey FA. Structure and Interactions at the Viral Surface of the Envelope Protein E1 of Semliki Forest Virus. Structure 2006; 14:75-86. [PMID: 16407067 DOI: 10.1016/j.str.2005.09.014] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2005] [Revised: 09/19/2005] [Accepted: 09/19/2005] [Indexed: 11/28/2022]
Abstract
Semliki Forest virus (SFV) is enveloped by a lipid bilayer enclosed within a glycoprotein cage made by glycoproteins E1 and E2. E1 is responsible for inducing membrane fusion, triggered by exposure to the acidic environment of the endosomes. Acidic pH induces E1/E2 dissociation, allowing E1 to interact with the target membrane, and, at the same time, to rearrange into E1 homotrimers that drive the membrane fusion reaction. We previously reported a preliminary Calpha trace of the monomeric E1 glycoprotein ectodomain and its organization on the virus particle. We also reported the 3.3 A structure of the trimeric, fusogenic conformation of E1. Here, we report the crystal structure of monomeric E1 refined to 3 A resolution and describe the amino acids involved in contacts in the virion. These results identify the major determinants for the E1/E2 icosahedral shell formation and open the way to rational mutagenesis approaches to shed light on SFV assembly.
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Affiliation(s)
- Alain Roussel
- Laboratoire de Virologie Moléculaire and Structurale, UMR 2472/1157 CNRS-INRA and IFR 115, 91198 Gif-sur-Yvette Cedex, France
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15
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Koschinski A, Wengler G, Wengler G, Repp H. Rare earth ions block the ion pores generated by the class II fusion proteins of alphaviruses and allow analysis of the biological functions of these pores. J Gen Virol 2005; 86:3311-3320. [PMID: 16298976 DOI: 10.1099/vir.0.81096-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recently, class II fusion proteins have been identified on the surface of alpha- and flaviviruses. These proteins have two functions besides membrane fusion: they generate an isometric lattice on the viral surface and they form ion-permeable pores at low pH. An attempt was made to identify inhibitors for the ion pores generated by the fusion proteins of the alphaviruses Semliki Forest virus and Sindbis virus. These pores can be detected and analysed in three situations: (i) in the target membrane during virus entry, by performing patch-clamp measurements of membrane currents; (ii) in the virus particle, by studying the entry of propidium iodide; and (iii) in the plasma membrane of infected cells, by Fura-2 fluorescence imaging of Ca2+ entry into infected cells. It is shown here that, at a concentration of 0·1 mM, rare earth ions block the ion permeability of alphavirus ion pores in all three situations. Even at a concentration of 0·5 mM, these ions do not block formation of the viral fusion pore, as they do not inhibit entry or multiplication of alphaviruses. The data indicate that ions flow through the ion pores into the virus particle in the endosome and from the endosome into the cytoplasm after fusion of the viral envelope with the endosomal membrane. These ion flows, however, are not necessary for productive infection. The possibility that the ability of class II fusion proteins to form ion-permeable pores reflects their origin from protein toxins that form ion-permeable pores, and that entry via class II fusion proteins may resemble the entry of non-enveloped viruses, is discussed.
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Affiliation(s)
- Andreas Koschinski
- Rudolf-Buchheim-Institut für Pharmakologie, Justus-Liebig-Universität, D-35392 Giessen, Germany
| | - Gerd Wengler
- Institut für Virologie, Fachbereich Veterinärmedizin, Justus-Liebig-Universität, D-35392 Giessen, Germany
| | - Gisela Wengler
- Institut für Virologie, Fachbereich Veterinärmedizin, Justus-Liebig-Universität, D-35392 Giessen, Germany
| | - Holger Repp
- Rudolf-Buchheim-Institut für Pharmakologie, Justus-Liebig-Universität, D-35392 Giessen, Germany
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16
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Nelson S, Hernandez R, Ferreira D, Brown DT. In vivo processing and isolation of furin protease-sensitive alphavirus glycoproteins: a new technique for producing mutations in virus assembly. Virology 2005; 332:629-39. [PMID: 15680428 DOI: 10.1016/j.virol.2004.12.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Revised: 11/29/2004] [Accepted: 12/14/2004] [Indexed: 12/19/2022]
Abstract
Sindbis virus particles are composed of three structural proteins (Capsid/E2/E1). In the mature virion the E1 glycoprotein is organized in a highly constrained, energy-rich conformation. It is hypothesized that this energy is utilized to drive events that deliver the viral genome to the cytoplasm of a host cell. The extraction of the E1 glycoprotein from virus membranes with detergent results in disulfide-bridge rearrangement and the collapse of the protein to a number of low-energy, non-native configurations. In a new approach to the production of membrane-free membrane glycoproteins, furin protease recognition motifs were installed at various positions in the E1 glycoprotein ectodomain. Proteins containing the furin-sensitive sites undergo normal folding and assembly in the endoplasmic reticulum and only experience the consequence of the mutation during transport to the cell surface. Processing by furin in the Golgi results in the release of the protein from the membrane. Processing of the proteins also impacts the envelopment of the nucleocapsid in the modified plasma membrane. This technique provides a unique method for studying the mechanism of virus assembly and protein structure without altering crucial early events in protein assembly, folding, and maturation.
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Affiliation(s)
- Steevenson Nelson
- Department of Molecular and Structural Biochemistry, North Carolina State University, Campus Box 7622, Raleigh NC 27695-7622, USA
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17
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Affiliation(s)
- Richard J Kuhn
- Markey Center for Structural Biology, Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
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18
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Gibbons DL, Reilly B, Ahn A, Vaney MC, Vigouroux A, Rey FA, Kielian M. Purification and crystallization reveal two types of interactions of the fusion protein homotrimer of Semliki Forest virus. J Virol 2004; 78:3514-23. [PMID: 15016874 PMCID: PMC371082 DOI: 10.1128/jvi.78.7.3514-3523.2004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The fusion proteins of the alphaviruses and flaviviruses have a similar native structure and convert to a highly stable homotrimer conformation during the fusion of the viral and target membranes. The properties of the alpha- and flavivirus fusion proteins distinguish them from the class I viral fusion proteins, such as influenza virus hemagglutinin, and establish them as the first members of the class II fusion proteins. Understanding how this new class carries out membrane fusion will require analysis of the structural basis for both the interaction of the protein subunits within the homotrimer and their interaction with the viral and target membranes. To this end we report a purification method for the E1 ectodomain homotrimer from the alphavirus Semliki Forest virus. The purified protein is trimeric, detergent soluble, retains the characteristic stability of the starting homotrimer, and is free of lipid and other contaminants. In contrast to the postfusion structures that have been determined for the class I proteins, the E1 homotrimer contains the fusion peptide region responsible for interaction with target membranes. This E1 trimer preparation is an excellent candidate for structural studies of the class II viral fusion proteins, and we report conditions that generate three-dimensional crystals suitable for analysis by X-ray diffraction. Determination of the structure will provide our first high-resolution views of both the low-pH-induced trimeric conformation and the target membrane-interacting region of the alphavirus fusion protein.
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Affiliation(s)
- Don L Gibbons
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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19
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Gibbons DL, Erk I, Reilly B, Navaza J, Kielian M, Rey FA, Lepault J. Visualization of the target-membrane-inserted fusion protein of Semliki Forest virus by combined electron microscopy and crystallography. Cell 2003; 114:573-83. [PMID: 13678581 DOI: 10.1016/s0092-8674(03)00683-4] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Semliki Forest virus enters cells by receptor-mediated endocytosis. The acidic environment of the endosome triggers a membrane fusion reaction that is mediated by the E1 glycoprotein. During fusion, E1 rearranges from an E1/E2 heterodimer to a highly stable, membrane-inserted E1 homotrimer (E1HT). In this study, we analyzed E1HT by a combination of electron cryomicroscopy, electron crystallography of negatively stained 2D crystals, and fitting of the available X-ray structure of the monomeric E1 ectodomain into the resulting 3D reconstruction. The visualized E1HT reveals that the ectodomain has reoriented vertically and inserted the distal tip of domain II into the lipid bilayer. Our data allow the visualization of a viral fusion protein inserted in its target membrane and demonstrate that insertion is a cooperative process, resulting in rings composed of five to six homotrimers.
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Affiliation(s)
- Don L Gibbons
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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20
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Koschinski A, Wengler G, Wengler G, Repp H. The membrane proteins of flaviviruses form ion-permeable pores in the target membrane after fusion: identification of the pores and analysis of their possible role in virus infection. J Gen Virol 2003; 84:1711-1721. [PMID: 12810864 DOI: 10.1099/vir.0.19062-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recently, we presented evidence that the E1 fusion protein of the alphavirus Semliki Forest virus forms ion-permeable pores in the target membrane after fusion. We proposed that the homologous fusion proteins of flaviviruses and hepatitis C virus form similar pores. To test this hypothesis for the E fusion protein of flaviviruses, the release of [(3)H]choline from liposomes by the flavivirus West Nile (WN) virus was determined. [(3)H]Choline was released at mildly acid pH. The pH threshold depended on the lipid composition. Release from certain liposomes was activated even at neutral pH. To identify the generation of individual pores, single cells were investigated with the patch-clamp technique. The formation of individual pores during low pH-induced WN virus entry at the plasma membrane occurred within seconds. These experiments were performed in parallel with Semliki Forest virus. The results indicated that, similar to alphavirus infection, infection with flaviviruses via endosomes leads to the formation of ion-permeable pores in the endosome after fusion, which allows the flow of protons from the endosome into the cytoplasm during virus entry. However, in vitro translation experiments of viral cores showed that, in contrast to alphaviruses, which probably need this proton flow for core disassembly, the genome RNA of WN virus present in the viral core is directly accessible for translation. For entry of flaviviruses, therefore, a second pathway for productive infection may exist, in which fusion of the viral membrane is activated at neutral pH by contact with a plasma membrane of appropriate lipid composition.
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Affiliation(s)
- Andreas Koschinski
- Rudolf-Buchheim-Institut für Pharmakologie1, Justus-Liebig-Universität, D-35392 Giessen, Germany
| | - Gerd Wengler
- Institut für Virologie der Veterinärmedizin2, Justus-Liebig-Universität, D-35392 Giessen, Germany
| | - Gisela Wengler
- Institut für Virologie der Veterinärmedizin2, Justus-Liebig-Universität, D-35392 Giessen, Germany
| | - Holger Repp
- Rudolf-Buchheim-Institut für Pharmakologie1, Justus-Liebig-Universität, D-35392 Giessen, Germany
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21
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Sjöberg M, Garoff H. Interactions between the transmembrane segments of the alphavirus E1 and E2 proteins play a role in virus budding and fusion. J Virol 2003; 77:3441-50. [PMID: 12610119 PMCID: PMC149539 DOI: 10.1128/jvi.77.6.3441-3450.2003] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The alphavirus envelope is built by heterodimers of the membrane proteins E1 and E2. The complex is formed as a p62E1 precursor in the endoplasmic reticulum. During transit to the plasma membrane (PM), it is cleaved into mature E1-E2 heterodimers, which are oligomerized into trimeric complexes, so-called spikes that bind both to each other and, at the PM, also to nucleocapsid (NC) structures under the membrane. These interactions drive the budding of new virus particles from the cell surface. The virus enters new cells by a low-pH-induced membrane fusion event where both inter- and intraheterodimer interactions are reorganized to establish a fusion-active membrane protein complex. There are no intact heterodimers left after fusion activation; instead, an E1 homotrimer remains in the cellular (or viral) membrane. We analyzed whether these transitions depend on interactions in the transmembrane (TM) region of the heterodimer. We observed a pattern of conserved glycines in the TM region of E1 and made two mutants where either the glycines only (SFV/E1(4L)) or the whole segment around the glycines (SFV/E1(11L)) was replaced by leucines. We found that both mutations decreased the stability of the heterodimer and increased the formation of the E1 homotrimer at a suboptimal fusion pH, while the fusion activity was decreased. This suggested that TM interactions play a role in virus assembly and entry and that anomalous or uncoordinated protein reorganizations take place in the mutants. In addition, the SFV/E1(11L) mutant was completely deficient in budding, which may reflect an inability to form multivalent NC interactions at the PM.
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Affiliation(s)
- Mathilda Sjöberg
- Department of Biosciences at Novum, Karolinska Institute, S-141 57 Huddinge, Sweden.
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22
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Hammar L, Markarian S, Haag L, Lankinen H, Salmi A, Cheng RH. Prefusion rearrangements resulting in fusion Peptide exposure in Semliki forest virus. J Biol Chem 2003; 278:7189-98. [PMID: 12493775 DOI: 10.1074/jbc.m206015200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Semliki Forest virus (SFV), like many enveloped viruses, takes advantage of the low pH in the endosome to convert into a fusion-competent configuration and complete infection by fusion with the endosomal membrane. Unlike influenza virus, carrying an N-terminal fusion peptide, SFV represents a less-well understood fusion principle involving an endosequence fusion peptide. To explore the series of events leading to a fusogenic configuration of the SFV, we exposed the virus to successive acidification, mimicking endosomal conditions, and followed structural rearrangements at probed sensor surfaces. Thus revealed, the initial phase involves a transient appearance of a non-linear neutralizing antibody epitope in the fusion protein, E1. Concurrent with the disappearance of this epitope, a set of masked sequences in proteins E1 and E2 became exposed. When pH reached 6.0-5.9 the virion transformed into a configuration of enlarged diameter with the fusion peptide optimally exposed. Simultaneously, a partly hidden sequence close to the receptor binding site in E2 became fully uncovered. At this presumably fusogenic stage, maximally 80 fusion peptide-identifying antibody Fab fragments could be bound per virion, i.e. one ligand per three copies of the fusion protein. The phenomena observed are discussed in terms of alphavirus structure and reported functional domains.
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Affiliation(s)
- Lena Hammar
- Department of Biosciences, Karolinska Institute, Huddinge S-141 57, Sweden.
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23
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Wengler G, Koschinski A, Wengler G, Dreyer F. Entry of alphaviruses at the plasma membrane converts the viral surface proteins into an ion-permeable pore that can be detected by electrophysiological analyses of whole-cell membrane currents. J Gen Virol 2003; 84:173-181. [PMID: 12533714 DOI: 10.1099/vir.0.18696-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
Alphaviruses are small enveloped viruses that have been used extensively as model enveloped viruses. During infection, virus particles are taken up into endosomes, where a low pH activates the viral fusion protein, E1. Fusion of the viral and the endosomal membranes releases the viral core into the cytoplasm where cores are disassembled by interaction with 60S ribosomal subunits. Recently, we have shown that in vitro this disassembly is strongly stimulated by low pH. We have proposed that after entry of the core into the cytoplasm, the viral membrane proteins that have been transferred to the endosomal membrane form an ion-permeable pore in the endosome. The resulting flow of protons from the endosome into the cytoplasm through this pore could generate a low-pH environment for core disassembly in vivo. Here we report two types of analysis aimed at the identification of such pores. First, the release of [3H]choline from the interior of liposomes was analysed in the presence of virus particles and viral proteins. Secondly, cells were infected with Sindbis or Semliki Forest alphaviruses at the plasma membrane and the possible generation of ion-permeable pores during this process was analysed by whole-cell voltage clamp analysis of the membrane current. The results obtained indicated that the proposed pores are in fact generated and allowed us to identify the formation of individual pores. Available evidence indicates that the alphavirus E1 protein probably forms these pores. Proteins homologous to the alphavirus E1 protein are present in flaviviruses and hepatitis C virus.
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Affiliation(s)
| | - Andreas Koschinski
- Rudolf-Buchheim-Institut für Pharmakologie, Justus-Liebig-Universität, D-35392 Giessen, Germany
| | | | - Florian Dreyer
- Rudolf-Buchheim-Institut für Pharmakologie, Justus-Liebig-Universität, D-35392 Giessen, Germany
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24
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Zhang W, Mukhopadhyay S, Pletnev SV, Baker TS, Kuhn RJ, Rossmann MG. Placement of the structural proteins in Sindbis virus. J Virol 2002; 76:11645-58. [PMID: 12388725 PMCID: PMC136788 DOI: 10.1128/jvi.76.22.11645-11658.2002] [Citation(s) in RCA: 174] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2002] [Accepted: 08/08/2002] [Indexed: 11/20/2022] Open
Abstract
The structure of the lipid-enveloped Sindbis virus has been determined by fitting atomic resolution crystallographic structures of component proteins into an 11-A resolution cryoelectron microscopy map. The virus has T=4 quasisymmetry elements that are accurately maintained between the external glycoproteins, the transmembrane helical region, and the internal nucleocapsid core. The crystal structure of the E1 glycoprotein was fitted into the cryoelectron microscopy density, in part by using the known carbohydrate positions as restraints. A difference map showed that the E2 glycoprotein was shaped similarly to E1, suggesting a possible common evolutionary origin for these two glycoproteins. The structure shows that the E2 glycoprotein would have to move away from the center of the trimeric spike in order to expose enough viral membrane surface to permit fusion with the cellular membrane during the initial stages of host infection. The well-resolved E1-E2 transmembrane regions form alpha-helical coiled coils that were consistent with T=4 symmetry. The known structure of the capsid protein was fitted into the density corresponding to the nucleocapsid, revising the structure published earlier.
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Affiliation(s)
- Wei Zhang
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-1392, USA
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25
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Gibbons DL, Kielian M. Molecular dissection of the Semliki Forest virus homotrimer reveals two functionally distinct regions of the fusion protein. J Virol 2002; 76:1194-205. [PMID: 11773395 PMCID: PMC135824 DOI: 10.1128/jvi.76.3.1194-1205.2002] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Semliki Forest virus (SFV) is an enveloped alphavirus that infects cells via a membrane fusion reaction triggered by the acidic pH of endosomes. In response to low pH, the E1 proteins on the virus membrane undergo a series of conformational changes, resulting in the formation of a stable E1 homotrimer. Little is known about the structural basis of either the E1 conformational changes or the resulting homotrimer or about the mechanism of action of the homotrimer in fusion. Here, the E1 homotrimer was formed in vitro from either virus or soluble E1 ectodomain and then probed by various perturbants, proteases, or glycosidase. The preformed homotrimer was extremely stable to moderately harsh conditions and proteases. By contrast, mild reducing conditions selectively disrupted the N-terminal region of trimeric E1, making it accessible to proteolytic cleavage and producing E1 fragments that retained trimer interactions. Trypsin digestion produced a fragment missing a portion of the N terminus just proximal to the putative fusion peptide. Digestion with elastase produced several fragments with cleavage sites between residues 78 and 102, resulting in the loss of the putative fusion peptide and the release of membrane-bound E1 ectodomain as a soluble trimer. Elastase also cleaved the homotrimer within an E1 loop located near the fusion peptide in the native E1 structure. Mass spectrometry was used to map the C termini of several differentially produced and fully functional E1 ectodomains. Together, our data identify two separate regions of the SFV E1 ectodomain, one responsible for target membrane association and one necessary for trimer interactions.
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Affiliation(s)
- Don L Gibbons
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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26
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Lescar J, Roussel A, Wien MW, Navaza J, Fuller SD, Wengler G, Wengler G, Rey FA. The Fusion glycoprotein shell of Semliki Forest virus: an icosahedral assembly primed for fusogenic activation at endosomal pH. Cell 2001; 105:137-48. [PMID: 11301009 DOI: 10.1016/s0092-8674(01)00303-8] [Citation(s) in RCA: 402] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Semliki Forest virus (SFV) has been extensively studied as a model for analyzing entry of enveloped viruses into target cells. Here we describe the trace of the polypeptide chain of the SFV fusion glycoprotein, E1, derived from an electron density map at 3.5 A resolution and describe its interactions at the surface of the virus. E1 is unexpectedly similar to the flavivirus envelope protein, with three structural domains disposed in the same primary sequence arrangement. These results introduce a new class of membrane fusion proteins which display lateral interactions to induce the necessary curvature and direct budding of closed particles. The resulting surface protein lattice is primed to cause membrane fusion when exposed to the acidic environment of the endosome.
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Affiliation(s)
- J Lescar
- Laboratoire de Génétique des Virus, CNRS-UPR 9053, 1, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
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27
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Mancini EJ, Clarke M, Gowen BE, Rutten T, Fuller SD. Cryo-electron microscopy reveals the functional organization of an enveloped virus, Semliki Forest virus. Mol Cell 2000; 5:255-66. [PMID: 10882067 DOI: 10.1016/s1097-2765(00)80421-9] [Citation(s) in RCA: 162] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Semliki Forest virus serves as a paradigm for membrane fusion and assembly. Our icosahedral reconstruction combined 5276 particle images from 48 cryo-electron micrographs and determined the virion structure to 9 A resolution. The improved resolution of this map reveals an N-terminal arm linking capsid subunits and defines the spike-capsid interaction sites. It illustrates the paired helical nature of the transmembrane segments and the elongated structures connecting them to the spike projecting domains. A 10 A diameter density in the fusion protein lines the cavity at the center of the spike. These clearly visible features combine with the variation in order between the layers to provide a framework for understanding the structural changes during the life cycle of an enveloped virus.
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Affiliation(s)
- E J Mancini
- The Structural Biology Programme, European Molecular Biology Laboratory, Heidelberg, Germany
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