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Biochemical Analysis of Coronavirus Spike Glycoprotein Conformational Intermediates during Membrane Fusion. J Virol 2019; 93:JVI.00785-19. [PMID: 31315988 PMCID: PMC6744234 DOI: 10.1128/jvi.00785-19] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 07/05/2019] [Indexed: 11/20/2022] Open
Abstract
A fusion protein expressed on the surface of enveloped viruses mediates fusion of the viral and cellular membranes to facilitate virus infection. Pre- and postfusion structures of viral fusion proteins have been characterized, but conformational changes between them remain poorly understood. Here, we examined the intermediate conformation of the murine coronavirus fusion protein, called the spike protein, which must be cleaved by a cellular protease following receptor binding. Western blot analysis of protease digestion products revealed that two subunits (67 and 69 kDa) are produced from a single spike protein (180 kDa). These two subunits were considered to be by-products derived from conformational changes and were useful for probing the intermediate conformation of the spike protein. Interaction with a heptad repeat (HR) peptide revealed that these subunits adopt packed and unpacked conformations, respectively, and two-dimensional electrophoresis revealed a trimeric assembly. Based on biochemical observations, we propose an asymmetric trimer model for the intermediate structure of the spike protein. Receptor binding induces the membrane-binding potential of the trimer, in which at least one HR motif forms a packed-hairpin structure, while membrane fusion subunits are covered by the receptor-binding subunit, thereby preventing the spike protein from forming the typical homotrimeric prehairpin structure predicted by the current model of class I viral fusion protein. Subsequent proteolysis induces simultaneous packing of the remaining unpacked HRs upon assembly of three HRs at the central axis to generate a six-helix bundle. Our model proposes a key mechanism for membrane fusion of enveloped viruses.IMPORTANCE Recent studies using single-particle cryo-electron microscopy (cryoEM) revealed the mechanism underlying activation of viral fusion protein at the priming stage. However, characterizing the subsequent triggering stage underpinning transition from pre- to postfusion structures is difficult because single-particle cryoEM excludes unstable structures that appear as heterogeneous shapes. Therefore, population-based biochemical analysis is needed to capture features of unstable proteins. Here, we analyzed protease digestion products of a coronavirus fusion protein during activation; their sizes appear to be affected directly by the conformational state. We propose a model for the viral fusion protein in the intermediate state, which involves a compact structure and conformational changes that overcome steric hindrance within the three fusion protein subunits.
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Ma X, Lu M, Gorman J, Terry DS, Hong X, Zhou Z, Zhao H, Altman RB, Arthos J, Blanchard SC, Kwong PD, Munro JB, Mothes W. HIV-1 Env trimer opens through an asymmetric intermediate in which individual protomers adopt distinct conformations. eLife 2018; 7:e34271. [PMID: 29561264 PMCID: PMC5896952 DOI: 10.7554/elife.34271] [Citation(s) in RCA: 106] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 03/20/2018] [Indexed: 01/02/2023] Open
Abstract
HIV-1 entry into cells requires binding of the viral envelope glycoprotein (Env) to receptor CD4 and coreceptor. Imaging of individual Env molecules on native virions shows Env trimers to be dynamic, spontaneously transitioning between three distinct well-populated conformational states: a pre-triggered Env (State 1), a default intermediate (State 2) and a three-CD4-bound conformation (State 3), which can be stabilized by binding of CD4 and coreceptor-surrogate antibody 17b. Here, using single-molecule Fluorescence Resonance Energy Transfer (smFRET), we show the default intermediate configuration to be asymmetric, with individual protomers adopting distinct conformations. During entry, this asymmetric intermediate forms when a single CD4 molecule engages the trimer. The trimer can then transition to State 3 by binding additional CD4 molecules and coreceptor.
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Affiliation(s)
- Xiaochu Ma
- Department of Microbial PathogenesisYale University School of MedicineNew HavenUnited States
| | - Maolin Lu
- Department of Microbial PathogenesisYale University School of MedicineNew HavenUnited States
| | - Jason Gorman
- Vaccine Research Center, National Institute of Allergy and Infectious DiseasesNational Institutes of HealthBethesdaUnited States
| | - Daniel S Terry
- Department of Physiology and BiophysicsWeill Cornell Medical College of Cornell UniversityNew YorkUnited States
| | - Xinyu Hong
- Department of Microbial PathogenesisYale University School of MedicineNew HavenUnited States
| | - Zhou Zhou
- Department of Physiology and BiophysicsWeill Cornell Medical College of Cornell UniversityNew YorkUnited States
| | - Hong Zhao
- Department of Physiology and BiophysicsWeill Cornell Medical College of Cornell UniversityNew YorkUnited States
| | - Roger B Altman
- Department of Physiology and BiophysicsWeill Cornell Medical College of Cornell UniversityNew YorkUnited States
| | - James Arthos
- Laboratory of Immunoregulation, National Institute of Allergy and Infectious DiseasesNational Institutes of HealthBethesdaUnited States
| | - Scott C Blanchard
- Department of Physiology and BiophysicsWeill Cornell Medical College of Cornell UniversityNew YorkUnited States
| | - Peter D Kwong
- Vaccine Research Center, National Institute of Allergy and Infectious DiseasesNational Institutes of HealthBethesdaUnited States
| | - James B Munro
- Department of Molecular Biology and MicrobiologyTufts University School of MedicineBostonUnited States
| | - Walther Mothes
- Department of Microbial PathogenesisYale University School of MedicineNew HavenUnited States
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Pallesen J, Wang N, Corbett KS, Wrapp D, Kirchdoerfer RN, Turner HL, Cottrell CA, Becker MM, Wang L, Shi W, Kong WP, Andres EL, Kettenbach AN, Denison MR, Chappell JD, Graham BS, Ward AB, McLellan JS. Immunogenicity and structures of a rationally designed prefusion MERS-CoV spike antigen. Proc Natl Acad Sci U S A 2017; 114:E7348-E7357. [PMID: 28807998 PMCID: PMC5584442 DOI: 10.1073/pnas.1707304114] [Citation(s) in RCA: 786] [Impact Index Per Article: 112.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Middle East respiratory syndrome coronavirus (MERS-CoV) is a lineage C betacoronavirus that since its emergence in 2012 has caused outbreaks in human populations with case-fatality rates of ∼36%. As in other coronaviruses, the spike (S) glycoprotein of MERS-CoV mediates receptor recognition and membrane fusion and is the primary target of the humoral immune response during infection. Here we use structure-based design to develop a generalizable strategy for retaining coronavirus S proteins in the antigenically optimal prefusion conformation and demonstrate that our engineered immunogen is able to elicit high neutralizing antibody titers against MERS-CoV. We also determined high-resolution structures of the trimeric MERS-CoV S ectodomain in complex with G4, a stem-directed neutralizing antibody. The structures reveal that G4 recognizes a glycosylated loop that is variable among coronaviruses and they define four conformational states of the trimer wherein each receptor-binding domain is either tightly packed at the membrane-distal apex or rotated into a receptor-accessible conformation. Our studies suggest a potential mechanism for fusion initiation through sequential receptor-binding events and provide a foundation for the structure-based design of coronavirus vaccines.
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Affiliation(s)
- Jesper Pallesen
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037
| | - Nianshuang Wang
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755;
| | - Kizzmekia S Corbett
- Viral Pathogenesis Laboratory, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892
| | - Daniel Wrapp
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - Robert N Kirchdoerfer
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037
| | - Hannah L Turner
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037
| | - Christopher A Cottrell
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037
| | - Michelle M Becker
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232
| | - Lingshu Wang
- Virology Core, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892
| | - Wei Shi
- Virology Core, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892
| | - Wing-Pui Kong
- Virology Core, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892
| | - Erica L Andres
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232
| | - Arminja N Kettenbach
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
- Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Lebanon, NH 03756
| | - Mark R Denison
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - James D Chappell
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232
| | - Barney S Graham
- Viral Pathogenesis Laboratory, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892
| | - Andrew B Ward
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037;
| | - Jason S McLellan
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755;
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