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Xie M. Virus-Induced Cell Fusion and Syncytia Formation. Results Probl Cell Differ 2024; 71:283-318. [PMID: 37996683 DOI: 10.1007/978-3-031-37936-9_14] [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: 11/25/2023]
Abstract
Most enveloped viruses encode viral fusion proteins to penetrate host cell by membrane fusion. Interestingly, many enveloped viruses can also use viral fusion proteins to induce cell-cell fusion, both in vitro and in vivo, leading to the formation of syncytia or multinucleated giant cells (MGCs). In addition, some non-enveloped viruses encode specialized viral proteins that induce cell-cell fusion to facilitate viral spread. Overall, viruses that can induce cell-cell fusion are nearly ubiquitous in mammals. Virus cell-to-cell spread by inducing cell-cell fusion may overcome entry and post-entry blocks in target cells and allow evasion of neutralizing antibodies. However, molecular mechanisms of virus-induced cell-cell fusion remain largely unknown. Here, I summarize the current understanding of virus-induced cell fusion and syncytia formation.
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Affiliation(s)
- Maorong Xie
- Division of Infection and Immunity, UCL, London, UK.
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2
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Saadi F, Pal D, Sarma JD. Spike Glycoprotein Is Central to Coronavirus Pathogenesis-Parallel Between m-CoV and SARS-CoV-2. Ann Neurosci 2021; 28:201-218. [PMID: 35341224 PMCID: PMC8948335 DOI: 10.1177/09727531211023755] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2020] [Accepted: 03/24/2021] [Indexed: 01/04/2023] Open
Abstract
Coronaviruses (CoVs) are single-stranded, polyadenylated, enveloped RNA of positive polarity with a unique potential to alter host tropism. This has been exceptionally demonstrated by the emergence of deadly virus outbreaks of the past: Severe Acute Respiratory Syndrome (SARS-CoV) in 2003 and Middle East Respiratory Syndrome (MERS-CoV) in 2012. The 2019 outbreak by the new cross-species transmission of SARS-CoV-2 has put the world on alert. CoV infection is triggered by receptor recognition, membrane fusion, and successive viral entry mediated by the surface Spike (S) glycoprotein. S protein is one of the major antigenic determinants and the target for neutralizing antibodies. It is a valuable target in antiviral therapies because of its central role in cell-cell fusion, viral antigen spread, and host immune responses leading to immunopathogenesis. The receptor-binding domain of S protein has received greater attention as it initiates host attachment and contains major antigenic determinants. However, investigating the therapeutic potential of fusion peptide as a part of the fusion core complex assembled by the heptad repeats 1 and 2 (HR1 and HR2) is also warranted. Along with receptor attachment and entry, fusion mechanisms should also be explored for designing inhibitors as a therapeutic intervention. In this article, we review the S protein function and its role in mediating membrane fusion, spread, tropism, and its associated pathogenesis with notable therapeutic strategies focusing on results obtained from studies on a murine β-Coronavirus (m-CoV) and its associated disease process.
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Affiliation(s)
- Fareeha Saadi
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, Kolkata, West Bengal, India
| | - Debnath Pal
- Department of Computational and Data Sciences, Indian Institute of Science, Bengaluru, Karnataka, India
| | - Jayasri Das Sarma
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, Kolkata, West Bengal, India
- Department of Ophthalmology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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3
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Ahmad A, Rilla K, Zou J, Zhang W, Pyykkö I, Kinnunen P, Ranjan S. Enhanced gene expression by a novel designed leucine zipper endosomolytic peptide. Int J Pharm 2021; 601:120556. [PMID: 33798688 DOI: 10.1016/j.ijpharm.2021.120556] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 03/12/2021] [Accepted: 03/29/2021] [Indexed: 11/18/2022]
Abstract
An endosomal trap is a major barrier in gene therapy. We have designed an endosomolytic peptide based on the leucine zipper sequence and characterized it both structurally and functionally. The results illustrated that leucine zipper endosomolytic peptide (LZEP) exhibited appreciable hemolysis of human red blood cells (hRBCs) at pH 5.0, but negligible hemolysis at pH 7.4. Calcein release experiment indicated that only at pH 5.0 but not at pH 7.4, LZEP was able to permeabilize hRBCs. LZEP revealed significant self-assembly as well as peptide induced α-helical structure at pH 5.0. Unlike at pH 5.0, LZEP failed to self-assemble and showed a random coil structure at pH 7.4. Transfection data depicted that lipoplexes modified with LZEP resulted in significantly higher gene expression as compared to lipoplexes without LZEP. Interestingly, the transfection efficacy of LZEP modified lipid nanoparticles reached the levels of Lipofectamine 2000 (LF 2000), without any cellular toxicity as observed by MTT assay. The results suggest a novel approach for designing endosomolytic peptides by employing the leucine zipper sequence and simultaneously the designed peptides could be utilized for enhancing gene delivery into mammalian cells.
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Affiliation(s)
- Aqeel Ahmad
- Helsinki Biophysics and Biomembrane Group, Department of Biomedical Engineering and Computational Sciences, Aalto University, Espoo, Finland; Department of Medical Biochemistry, College of Medicine, Shaqra University, Shaqra, 11961, Saudi Arabia
| | - Kirsi Rilla
- Institute of Biomedicine, University of Eastern Finland, 70211 Kuopio, Finland
| | - Jing Zou
- Hearing and Balance Research Unit, Field of Otolaryngology, School of Medicine, Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland; Department of Otolaryngology, Head and Neck Surgery, Center for Otolaryngology-Head & Neck Surgery of Chinese PLA, Changhai Hospital, Second Military Medical University, Shanghai, China
| | - Weikai Zhang
- Hearing and Balance Research Unit, Field of Otolaryngology, School of Medicine, Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland; Department of Orthopaedic Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Ilmari Pyykkö
- Hearing and Balance Research Unit, Field of Otolaryngology, School of Medicine, Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Paavo Kinnunen
- Helsinki Biophysics and Biomembrane Group, Department of Biomedical Engineering and Computational Sciences, Aalto University, Espoo, Finland
| | - Sanjeev Ranjan
- Helsinki Biophysics and Biomembrane Group, Department of Biomedical Engineering and Computational Sciences, Aalto University, Espoo, Finland; Institute of Biomedicine, University of Eastern Finland, 70211 Kuopio, Finland.
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Abstract
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has recently caused acute respiratory distress syndrome affecting more than 200 countries with varied mortality rate. Successive genetic variants of SARS-CoV-2 become evident across the globe immediately after its complete genome sequencing. Here, we found a decent association of SARS-CoV-2 ORF3a mutation with higher mortality rate. Extensive in silico studies revealed several amino acid changes in ORF3a protein which ultimately leads to diverse structural modifications like B cell epitope loss, gain/loss of phosphorylation site and loss of leucine zipper motif. We could further relate these changes to the enhanced antigenic diversity of SARS-CoV-2. Through protein−protein network analysis and functional annotation studies, we obtained a close federation of ORF3a protein with host immune response via divergent signal transduction pathways including JAK-STAT, chemokine and cytokine-related pathways. Our data not only unveil the fairly appreciable association of ORF3a mutation with higher mortality rate, but also suggest a potential mechanistic insight towards the immunopathogenic manifestation of SARS-CoV-2 infection.
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Eddy NR, Onuchic JN. Rotation-Activated and Cooperative Zipping Characterize Class I Viral Fusion Protein Dynamics. Biophys J 2019; 114:1878-1888. [PMID: 29694865 DOI: 10.1016/j.bpj.2018.03.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Revised: 02/15/2018] [Accepted: 03/06/2018] [Indexed: 11/19/2022] Open
Abstract
Class I viral fusion proteins are α-helical proteins that facilitate membrane fusion between viral and host membranes through large conformational transitions. Although prefusion and postfusion crystal structures have been solved for many of these proteins, details about how they transition between these states have remained elusive. This work presents the first, to our knowledge, computational survey of transitions between pre- and postfusion configurations for several class I viral fusion proteins using structure-based models to analyze their dynamics. As suggested by their structural similarities, all proteins share common mechanistic features during their transitions that can be characterized by a diffusive rotational search followed by cooperative N- and C-terminal zipping. Instead of predicting a stable spring-loaded intermediate, our model suggests that helical bundle formation is mediated by N- and C-terminal interactions late in the transition. Shared transition features suggest a global mechanism in which fusion is activated by slow protein-core rotation.
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Affiliation(s)
- Nathanial R Eddy
- Department of Physics and Astronomy; Center for Theoretical Biological Physics, Rice University, Houston, Texas
| | - José N Onuchic
- Department of Physics and Astronomy; Center for Theoretical Biological Physics, Rice University, Houston, Texas.
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Modulation of anti-endotoxin property of Temporin L by minor amino acid substitution in identified phenylalanine zipper sequence. Biochem J 2016; 473:4045-4062. [PMID: 27609815 DOI: 10.1042/bcj20160713] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Accepted: 09/07/2016] [Indexed: 11/17/2022]
Abstract
A 13-residue frog antimicrobial peptide Temporin L (TempL) possesses versatile antimicrobial activities and is considered a lead molecule for the development of new antimicrobial agents. To find out the amino acid sequences that influence the anti-microbial property of TempL, a phenylalanine zipper-like sequence was identified in it which was not reported earlier. Several alanine-substituted analogs and a scrambled peptide having the same composition of TempL were designed for evaluating the role of this motif. To investigate whether leucine residues instead of phenylalanine residues at 'a' and/or 'd' position(s) of the heptad repeat sequence could alter its antimicrobial property, several TempL analogs were synthesized after replacing these phenylalanine residues with leucine residues. Replacing phenylalanine residues with alanine residues in the phenylalanine zipper sequence significantly compromised the anti-endotoxin property of TempL. This is evident from the higher production of tumor necrosis factor-α and interleukin-6 in lipopolysaccharide (LPS)-stimulated rat bone-marrow-derived macrophage cells in the presence of its alanine-substituted analogs than TempL itself. However, replacement of these phenylalanine residues with leucine residues significantly augmented anti-endotoxin property of TempL. A single alanine-substituted TempL analog (F8A-TempL) showed significantly reduced cytotoxicity but retained the antibacterial activity of TempL, while the two single leucine-substituted analogs (F5L-TempL and F8L-TempL), although exhibiting lower cytotoxicity, were able to retain the antibacterial activity of the parent peptide. The results demonstrate how minor amino acid substitutions in the identified phenylalanine zipper sequence in TempL could yield analogs with better antibacterial and/or anti-endotoxin properties with their plausible mechanism of action.
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Xie W, Wen H, Chu F, Yan S, Xie W, Lin B, Chen Y, Li Z, Ren G, Song Y, Zhao L, Wang Z. Mutations in the Leucine Zipper-Like Motif of the Human Parainfluenza Virus 3 Fusion Protein Impair Fusion Activity. Intervirology 2015; 58:297-309. [PMID: 26694747 PMCID: PMC7179560 DOI: 10.1159/000441978] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 10/24/2015] [Indexed: 01/28/2023] Open
Abstract
Objective To investigate the effect of the leucine zipper-like motif between HRA and HRB of the human parainfluenza virus 3 fusion protein on fusion activity. Methods Site-directed mutagenesis was utilized to substitute the heptadic residues at 257, 264, 271, 278, 285, 292, and 299 in this motif with alanine. Additionally, 3 middle heptadic leucine residues at 271, 278, and 285 were replaced with alanine singly or in combination. A vaccinia virus-T7 RNA polymerase transient expression system was employed to express the wild-type or mutated fusion (F) proteins. Three different types of membrane fusion assays were performed to analyze the fusogenic activity, fluorescence-activated cell sorting (FACS) analysis was executed to examine the cell surface expression level, and a coimmunoprecipitation assay was conducted to probe the hemagglutinin-neuraminidase (HN)-F interaction at the cell surface. Results All of the substitutions in this motif exhibited diminished or even lost fusion activity in all stages of fusion, although they all had no effect on cell surface expression. In the coimmunoprecipitation assay, all mutants resulted in decreased detection of the HN-F complexes compared with that of the wild-type F protein. Conclusions This motif has an important influence on fusion activity, and its integrality is indispensable for membrane fusion.
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Affiliation(s)
- Wenyan Xie
- Department of Virology, School of Public Health, Shandong University, Jinan, PR China
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Azmi S, Srivastava S, Mishra NN, Tripathi JK, Shukla PK, Ghosh JK. Characterization of antimicrobial, cytotoxic, and antiendotoxin properties of short peptides with different hydrophobic amino acids at "a" and "d" positions of a heptad repeat sequence. J Med Chem 2013; 56:924-39. [PMID: 23324083 DOI: 10.1021/jm301407k] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
To understand the influence of different hydrophobic amino acids at "a" and "d" positions of a heptad repeat sequence on antimicrobial, cytotoxic, and antiendotoxin properties, four 15-residue peptides with leucine (LRP), phenylalanine (FRP), valine (VRP), and alanine (ARP) residues at these positions were designed, synthesized, and characterized. Although valine is similarly hydrophobic to leucine and phenylalanine, VRP showed significantly lesser cytotoxicity than LRP and FRP; further, the replacement of leucines with valines at "a" and "d" positions of melittin-heptads drastically reduced its cytotoxicity. However, all four peptides exhibited significant antimicrobial activities that correlate well with their interactions with mammalian and bacterial cell membranes and the corresponding lipid vesicles. LRP most efficiently neutralized the LPS-induced pro-inflammatory mediators like NO, TNF-α, and IL-6 in macrophages followed by FRP, VRP, and ARP. The results could be useful for designing short antimicrobial and antiendotoxin peptides with understanding the basis of their activity.
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Affiliation(s)
- Sarfuddin Azmi
- Molecular and Structural Biology Division, CSIR-Central Drug Research Institute , Lucknow 226 001, India
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Belouzard S, Millet JK, Licitra BN, Whittaker GR. Mechanisms of coronavirus cell entry mediated by the viral spike protein. Viruses 2012; 4:1011-33. [PMID: 22816037 PMCID: PMC3397359 DOI: 10.3390/v4061011] [Citation(s) in RCA: 878] [Impact Index Per Article: 73.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Revised: 06/13/2012] [Accepted: 06/14/2012] [Indexed: 12/12/2022] Open
Abstract
Coronaviruses are enveloped positive-stranded RNA viruses that replicate in the cytoplasm. To deliver their nucleocapsid into the host cell, they rely on the fusion of their envelope with the host cell membrane. The spike glycoprotein (S) mediates virus entry and is a primary determinant of cell tropism and pathogenesis. It is classified as a class I fusion protein, and is responsible for binding to the receptor on the host cell as well as mediating the fusion of host and viral membranes—A process driven by major conformational changes of the S protein. This review discusses coronavirus entry mechanisms focusing on the different triggers used by coronaviruses to initiate the conformational change of the S protein: receptor binding, low pH exposure and proteolytic activation. We also highlight commonalities between coronavirus S proteins and other class I viral fusion proteins, as well as distinctive features that confer distinct tropism, pathogenicity and host interspecies transmission characteristics to coronaviruses.
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Affiliation(s)
- Sandrine Belouzard
- Center for Infection and Immunity of Lille, CNRS UMR8204, INSERM U1019, Institut Pasteur de Lille, Université Lille Nord de France, 59000 Lille, France;
| | - Jean K. Millet
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA; (J.K.M.); (B.N.L.)
| | - Beth N. Licitra
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA; (J.K.M.); (B.N.L.)
| | - Gary R. Whittaker
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY 14853, USA; (J.K.M.); (B.N.L.)
- Author to whom correspondence should be addressed; ; Tel.: +1-607-253-4021; Fax: +1-607-253-3384
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10
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Xiao S, Yang L, Li F. The structure and assembly model of the third transmembrane domain of Slc11a1 in SDS micelles revealed by NMR study of the Leu-substituted peptide. J Pept Sci 2011; 18:45-51. [DOI: 10.1002/psc.1414] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2011] [Revised: 07/18/2011] [Accepted: 08/03/2011] [Indexed: 11/09/2022]
Affiliation(s)
- Shuyan Xiao
- State Key Laboratory of Supramolecular Structure and Materials; Jilin University; Changchun 130012 China
| | - Lei Yang
- State Key Laboratory of Supramolecular Structure and Materials; Jilin University; Changchun 130012 China
| | - Fei Li
- State Key Laboratory of Supramolecular Structure and Materials; Jilin University; Changchun 130012 China
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11
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Studies on the assembly of a leucine zipper antibacterial peptide and its analogs onto mammalian cells and bacteria. Amino Acids 2010; 40:749-59. [DOI: 10.1007/s00726-010-0744-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2010] [Accepted: 09/02/2010] [Indexed: 10/19/2022]
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Dosch SF, Mahajan SD, Collins AR. SARS coronavirus spike protein-induced innate immune response occurs via activation of the NF-kappaB pathway in human monocyte macrophages in vitro. Virus Res 2009; 142:19-27. [PMID: 19185596 PMCID: PMC2699111 DOI: 10.1016/j.virusres.2009.01.005] [Citation(s) in RCA: 188] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2008] [Accepted: 01/09/2009] [Indexed: 12/12/2022]
Abstract
A purified recombinant spike (S) protein was studied for its effect on stimulating human peripheral blood monocyte macrophages (PBMC). We examined inflammatory gene mRNA abundances found in S protein-treated PBMC using gene arrays. We identified differential mRNA abundances of genes with functional properties associated with antiviral (CXCL10) and inflammatory (IL-6 and IL-8) responses. We confirmed cytokine mRNA increases by real-time quantitative(q) RT-PCR or ELISA. We further analyzed the sensitivity and specificity of the prominent IL-8 response. By real-time qRT-PCR, S protein was shown to stimulate IL-8 mRNA accumulation in a dose dependent manner while treatment with E protein did not. Also, titration of S protein-specific production and secretion of IL-8 by ELISA showed that the dose of 5.6nM of S produced a significant increase in IL-8 (p=0.003) compared to mock-treated controls. The increase in IL-8 stimulated by a concentration of 5.6nM of S was comparable to concentrations seen for S protein binding to ACE2 or to neutralizing monoclonal antibody suggesting a physiological relevance. An NF-kappaB inhibitor, TPCK (N-Tosyl-L-Phenylalanine Chloromethyl Ketone) could suppress IL-8 production and secretion in response to S protein in PBMC and THP-1 cells and in HCoV-229E virus-infected PBMC. Activation and translocation of NF-kappaB was shown to occur rapidly following exposure of PBMC or THP-1 cells to S protein using a highly sensitive assay for active nuclear NF-kappaB p65 transcription factor. The results further suggested that released or secreted S protein could activate blood monocytes through recognition by toll-like receptor (TLR)2 ligand.
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Affiliation(s)
- Susan F. Dosch
- Department of Microbiology and Immunology, Division of Allergy, Immunology and Rheumatology, State University of New York at Buffalo, Buffalo, NY, United States
| | - Supriya D. Mahajan
- Department of Medicine, Division of Allergy, Immunology and Rheumatology, State University of New York at Buffalo, Buffalo, NY, United States
| | - Arlene R. Collins
- Department of Microbiology and Immunology, Division of Allergy, Immunology and Rheumatology, State University of New York at Buffalo, Buffalo, NY, United States
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Conserved leucines in N-terminal heptad repeat HR1 of envelope fusion protein F of group II nucleopolyhedroviruses are important for correct processing and essential for fusogenicity. J Virol 2007; 82:2437-47. [PMID: 18094156 DOI: 10.1128/jvi.01885-07] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The heptad repeat (HR), a conserved structural motif of class I viral fusion proteins, is responsible for the formation of a six-helix bundle structure during the envelope fusion process. The insect baculovirus F protein is a newly found budded virus envelope fusion protein which possesses common features to class I fusion proteins, such as proteolytic cleavage and the presence of an N-terminal open fusion peptide and multiple HR domains on the transmembrane subunit F(1). Similar to many vertebrate viral fusion proteins, a conserved leucine zipper motif is predicted in this HR region proximal to the fusion peptide in baculovirus F proteins. To facilitate our understanding of the functional role of this leucine zipper-like HR1 domain in baculovirus F protein synthesis, processing, and viral infectivity, key leucine residues (Leu209, Leu216, and Leu223) were replaced by alanine (A) or arginine (R), respectively. By using Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) as a pseudotype expression system, we demonstrated that all mutant F proteins incorporated into budded virus, indicating that leucine substitutions did not affect intercellular trafficking of F. Furin-like protease cleavage was not affected by any of the leucine substitutions; however, the disulfide bridging and N-linked glycosylation patterns were partly altered. Single substitutions in HR1 showed that the three leucine residues were critical for F fusogenicity and the rescue of AcMNPV infectivity. Our results support the view that the leucine zipper-like HR1 domain is important to safeguard the proper folding, glycosylation, and fusogenicity of baculovirus F proteins.
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Amino acid substitutions in the S2 subunit of mouse hepatitis virus variant V51 encode determinants of host range expansion. J Virol 2007; 82:1414-24. [PMID: 18032498 DOI: 10.1128/jvi.01674-07] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
We previously described mouse hepatitis virus (MHV) variant V51 derived from a persistent infection of murine DBT cells with an expanded host range (R. S. Baric, E. Sullivan, L. Hensley, B. Yount, and W. Chen, J. Virol. 73:638-649, 1999). Sequencing of the V51 spike gene, the mediator of virus entry, revealed 13 amino acid substitutions relative to the originating MHV A59 strain. Seven substitutions were located in the amino-terminal S1 cleavage subunit, and six were located in the carboxy-terminal S2 cleavage subunit. Using targeted RNA recombination, we constructed a panel of recombinant viruses to map the mediators of host range to the six substitutions in S2, with a subgroup of four changes of particular interest. This subgroup maps to two previously identified domains within S2, a putative fusion peptide and a heptad repeat, both conserved features of class I fusion proteins. In addition to an altered host range, V51 displayed altered utilization of CEACAM1a, the high-affinity receptor for A59. Interestingly, a recombinant with S1 from A59 and S2 from V51 was severely debilitated in its ability to productively infect cells via CEACAM1a, while the inverse recombinant was not. This result suggests that the S2 substitutions exert powerful effects on the fusion trigger that normally passes from S1 to S2. These novel findings play against the existing data that suggest that MHV host range determinants are located in the S1 subunit, which harbors the receptor binding domain, or involve coordinating changes in both S1 and S2. Mounting evidence also suggests that the class I fusion mechanism may possess some innate plasticity that regulates viral host range.
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Corver J, Broer R, van Kasteren P, Spaan W. GxxxG motif of severe acute respiratory syndrome coronavirus spike glycoprotein transmembrane domain is not involved in trimerization and is not important for entry. J Virol 2007; 81:8352-5. [PMID: 17507478 PMCID: PMC1951296 DOI: 10.1128/jvi.00014-07] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Recently, a paper was published in which it was proposed that the GxxxG motif of the severe acute respiratory syndrome (SARS) coronavirus spike (S) protein transmembrane domain plays a vital role in oligomerization of the protein (E. Arbely, Z. Granot, I. Kass, J. Orly, and I. T. Arkin, Biochemistry 45:11349-11356, 2006). Here, we show that the GxxxG motif is not involved in SARS S oligomerization by trimerization analysis of S GxxxG mutant proteins. In addition, the capability of S to mediate entry of SARS S-pseudotyped particles overall was affected moderately in the mutant proteins, also arguing for a nonvital role for the GxxxG motif in SARS coronavirus entry.
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Affiliation(s)
- Jeroen Corver
- Department of Medical Microbiology, Leiden University Medical Center, E4-P, P.O. Box 9600, 2300 RC Leiden, The Netherlands.
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Leth-Larsen R, Zhong F, Chow VTK, Holmskov U, Lu J. The SARS coronavirus spike glycoprotein is selectively recognized by lung surfactant protein D and activates macrophages. Immunobiology 2007; 212:201-11. [PMID: 17412287 PMCID: PMC7114820 DOI: 10.1016/j.imbio.2006.12.001] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2006] [Revised: 11/28/2006] [Accepted: 12/01/2006] [Indexed: 01/05/2023]
Abstract
The severe acute respiratory syndrome coronavirus (SARS-CoV) infects host cells with its surface glycosylated spike-protein (S-protein). Here we expressed the SARS-CoV S-protein to investigate its interactions with innate immune mechanisms in the lung. The purified S-protein was detected as a 210 kDa glycosylated protein. It was not secreted in the presence of tunicamycin and was detected as a 130 kDa protein in the cell lysate. The purified S-protein bound to Vero but not 293T cells and was itself recognized by lung surfactant protein D (SP-D), a collectin found in the lung alveoli. The binding required Ca2+ and was inhibited by maltose. The serum collectin, mannan-binding lectin (MBL), exhibited no detectable binding to the purified S-protein. S-protein binds and activates macrophages but not dendritic cells (DCs). It suggests that SARS-CoV interacts with innate immune mechanisms in the lung through its S-protein and regulates pulmonary inflammation.
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Affiliation(s)
- Rikke Leth-Larsen
- Department of Microbiology, National University of Singapore, Singapore
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Abstract
Coronaviruses are large, enveloped RNA viruses of both medical and veterinary importance. Interest in this viral family has intensified in the past few years as a result of the identification of a newly emerged coronavirus as the causative agent of severe acute respiratory syndrome (SARS). At the molecular level, coronaviruses employ a variety of unusual strategies to accomplish a complex program of gene expression. Coronavirus replication entails ribosome frameshifting during genome translation, the synthesis of both genomic and multiple subgenomic RNA species, and the assembly of progeny virions by a pathway that is unique among enveloped RNA viruses. Progress in the investigation of these processes has been enhanced by the development of reverse genetic systems, an advance that was heretofore obstructed by the enormous size of the coronavirus genome. This review summarizes both classical and contemporary discoveries in the study of the molecular biology of these infectious agents, with particular emphasis on the nature and recognition of viral receptors, viral RNA synthesis, and the molecular interactions governing virion assembly.
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Affiliation(s)
- Paul S Masters
- Wadsworth Center, New York State Department of Health, Albany, 12201, USA
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Tripet B, Kao DJ, Jeffers SA, Holmes KV, Hodges RS. Template-based coiled-coil antigens elicit neutralizing antibodies to the SARS-coronavirus. J Struct Biol 2006; 155:176-94. [PMID: 16697221 PMCID: PMC7129695 DOI: 10.1016/j.jsb.2006.03.019] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2006] [Accepted: 03/09/2006] [Indexed: 11/30/2022]
Abstract
The Spike (S) glycoprotein of coronaviruses (CoV) mediates viral entry into host cells. It contains two hydrophobic heptad repeat (HR) regions, denoted HRN and HRC, which oligomerize the S glycoprotein into a trimer in the native state and when activated collapse into a six-helix bundle structure driving fusion of the host and viral membranes. Previous studies have shown that peptides of the HR regions can inhibit viral infectivity. These studies imply that the HR regions are accessible and that agents which can interact with them may prevent viral entry. In the present study, we have investigated an approach to generate antibodies that specifically recognize the HRN and HRC regions of the SARS-CoV spike (S) glycoprotein in order to evaluate whether these antibodies can inhibit viral infectivity and thus neutralize the SARS-CoV. In this regard, we incorporated HRN and HRC coiled-coil surface residues into a de novo designed two-stranded α-helical coiled-coil template for generating conformation-specific antibodies that recognize α-helices in proteins (Lu, S.M., Hodges, R.S., 2002. J. Biol. Chem. 277, 23515–23524). Eighteen surface residues from two regions of HRN and HRC were incorporated into the template and used to generate four anti-sera, HRN1, HRN2, HRC1, and HRC2. Our results show that all of the elicited anti-sera can specifically recognize HRN or HRC peptides and the native SARS-CoV S protein in an ELISA format. Flow cytometry (FACS) analysis, however, showed only HRC1 and HRC2 anti-sera could bind to native S protein expressed on the cell surface of Chinese hamster ovary cells, i.e., the cell surface structure of the S glycoprotein precluded the ability of the HRN1 or HRN2 anti-sera to see their respective epitope sites. In in vitro viral infectivity assays, no inhibition was observed for either HRN1 or HRN2 anti-serum, whereas both HRC1 and HRC2 anti-sera could inhibit SARS-CoV infection in a dose-dependent manner. Interestingly, the HRC1 anti-serum, which was a more effective inhibitor of viral infectivity compared to HRC2 anti-serum, could only bind the pre-fusogenic state of HRC, i.e., the HRC1 anti-serum did not recognize the six-helix bundle conformation (fusion state) whereas HRC2 anti-serum did. These results suggest that antibodies that are more specific for the pre-fusogenic state of HRC may be better neutralizing antibodies. Overall, these results clearly demonstrate that the two-stranded coiled-coil template acts as an excellent presentation system for eliciting helix-specific antibodies against highly conserved viral antigens and HRC1 and HRC2 peptides may represent potential candidates for use in a peptide vaccine against the SARS-CoV.
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Affiliation(s)
- Brian Tripet
- Department of Biochemistry and Molecular Genetics, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045, USA
| | - Daniel J. Kao
- Department of Biochemistry and Molecular Genetics, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045, USA
| | - Scott A. Jeffers
- Department of Microbiology, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045, USA
| | - Kathryn V. Holmes
- Department of Microbiology, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045, USA
| | - Robert S. Hodges
- Department of Biochemistry and Molecular Genetics, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045, USA
- Corresponding author. Fax: +1 303 724 3249.
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19
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Broer R, Boson B, Spaan W, Cosset FL, Corver J. Important role for the transmembrane domain of severe acute respiratory syndrome coronavirus spike protein during entry. J Virol 2006; 80:1302-10. [PMID: 16415007 PMCID: PMC1346921 DOI: 10.1128/jvi.80.3.1302-1310.2006] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The spike protein (S) of severe acute respiratory syndrome coronavirus (SARS-CoV) is responsible for receptor binding and membrane fusion. It contains a highly conserved transmembrane domain that consists of three parts: an N-terminal tryptophan-rich domain, a central domain, and a cysteine-rich C-terminal domain. The cytoplasmic tail of S has previously been shown to be required for assembly. Here, the roles of the transmembrane and cytoplasmic domains of S in the infectivity and membrane fusion activity of SARS-CoV have been studied. SARS-CoV S-pseudotyped retrovirus (SARSpp) was used to measure S-mediated infectivity. In addition, the cell-cell fusion activity of S was monitored by a Renilla luciferase-based cell-cell fusion assay. S(VSV-Cyt), an S chimera with a cytoplasmic tail derived from vesicular stomatitis virus G protein (VSV-G), and S(MHV-TMDCyt), an S chimera with the cytoplasmic and transmembrane domains of mouse hepatitis virus, displayed wild-type-like activity in both assays. S(VSV-TMDCyt), a chimera with the cytoplasmic and transmembrane domains of VSV-G, was impaired in the SARSpp and cell-cell fusion assays, showing 3 to 25% activity compared to the wild type, depending on the assay and the cells used. Examination of the oligomeric state of the chimeric S proteins in SARSpp revealed that S(VSV-TMDCyt) trimers were less stable than wild-type S trimers, possibly explaining the lowered fusogenicity and infectivity.
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Affiliation(s)
- Rene Broer
- Department of Medical Microbiology, E4-P, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, The Netherlands
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20
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Weiss SR, Navas-Martin S. Coronavirus pathogenesis and the emerging pathogen severe acute respiratory syndrome coronavirus. Microbiol Mol Biol Rev 2006; 69:635-64. [PMID: 16339739 PMCID: PMC1306801 DOI: 10.1128/mmbr.69.4.635-664.2005] [Citation(s) in RCA: 739] [Impact Index Per Article: 41.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Coronaviruses are a family of enveloped, single-stranded, positive-strand RNA viruses classified within the Nidovirales order. This coronavirus family consists of pathogens of many animal species and of humans, including the recently isolated severe acute respiratory syndrome coronavirus (SARS-CoV). This review is divided into two main parts; the first concerns the animal coronaviruses and their pathogenesis, with an emphasis on the functions of individual viral genes, and the second discusses the newly described human emerging pathogen, SARS-CoV. The coronavirus part covers (i) a description of a group of coronaviruses and the diseases they cause, including the prototype coronavirus, murine hepatitis virus, which is one of the recognized animal models for multiple sclerosis, as well as viruses of veterinary importance that infect the pig, chicken, and cat and a summary of the human viruses; (ii) a short summary of the replication cycle of coronaviruses in cell culture; (iii) the development and application of reverse genetics systems; and (iv) the roles of individual coronavirus proteins in replication and pathogenesis. The SARS-CoV part covers the pathogenesis of SARS, the developing animal models for infection, and the progress in vaccine development and antiviral therapies. The data gathered on the animal coronaviruses continue to be helpful in understanding SARS-CoV.
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Affiliation(s)
- Susan R Weiss
- Department of Microbiology, University of Pennsylvania School of Medicine, 36th Street and Hamilton Walk, Philadelphia, Pennsylvania 19104-6076, USA.
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21
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Weiss SR, Navas-Martin S. Coronavirus pathogenesis and the emerging pathogen severe acute respiratory syndrome coronavirus. Microbiol Mol Biol Rev 2005. [PMID: 16339739 DOI: 10.1128/mmbr.69.4.635] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/21/2023] Open
Abstract
Coronaviruses are a family of enveloped, single-stranded, positive-strand RNA viruses classified within the Nidovirales order. This coronavirus family consists of pathogens of many animal species and of humans, including the recently isolated severe acute respiratory syndrome coronavirus (SARS-CoV). This review is divided into two main parts; the first concerns the animal coronaviruses and their pathogenesis, with an emphasis on the functions of individual viral genes, and the second discusses the newly described human emerging pathogen, SARS-CoV. The coronavirus part covers (i) a description of a group of coronaviruses and the diseases they cause, including the prototype coronavirus, murine hepatitis virus, which is one of the recognized animal models for multiple sclerosis, as well as viruses of veterinary importance that infect the pig, chicken, and cat and a summary of the human viruses; (ii) a short summary of the replication cycle of coronaviruses in cell culture; (iii) the development and application of reverse genetics systems; and (iv) the roles of individual coronavirus proteins in replication and pathogenesis. The SARS-CoV part covers the pathogenesis of SARS, the developing animal models for infection, and the progress in vaccine development and antiviral therapies. The data gathered on the animal coronaviruses continue to be helpful in understanding SARS-CoV.
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Affiliation(s)
- Susan R Weiss
- Department of Microbiology, University of Pennsylvania School of Medicine, 36th Street and Hamilton Walk, Philadelphia, Pennsylvania 19104-6076, USA.
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22
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Follis KE, York J, Nunberg JH. Serine-scanning mutagenesis studies of the C-terminal heptad repeats in the SARS coronavirus S glycoprotein highlight the important role of the short helical region. Virology 2005; 341:122-9. [PMID: 16081124 PMCID: PMC7111819 DOI: 10.1016/j.virol.2005.07.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2005] [Revised: 06/28/2005] [Accepted: 07/05/2005] [Indexed: 02/04/2023]
Abstract
The fusion subunit of the SARS-CoV S glycoprotein contains two regions of hydrophobic heptad-repeat amino acid sequences that have been shown in biophysical studies to form a six-helix bundle structure typical of the fusion-active core found in Class I viral fusion proteins. Here, we have applied serine-scanning mutagenesis to the C-terminal-most heptad-repeat region in the SARS-CoV S glycoprotein to investigate the functional role of this region in membrane fusion. We show that hydrophobic sidechains at a and d positions only within the short helical segment of the C-terminal heptad-repeat region (I1161, I1165, L1168, A1172, and L1175) are critical for cell–cell fusion. Serine mutations at outlying heptad-repeat residues that form an extended chain in the core structure (V1158, L1179, and L1182) do not affect fusogenicity. Our study provides genetic evidence for the important role of α-helical packing in promoting S glycoprotein-mediated membrane fusion.
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Affiliation(s)
- Kathryn E Follis
- Montana Biotechnology Center, The University of Montana, Science Complex Room 221, Missoula, MT 59812, USA
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23
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Omerović J, Lev L, Longnecker R. The amino terminus of Epstein-Barr virus glycoprotein gH is important for fusion with epithelial and B cells. J Virol 2005; 79:12408-15. [PMID: 16160168 PMCID: PMC1211543 DOI: 10.1128/jvi.79.19.12408-12415.2005] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Epstein-Barr virus (EBV) infects B lymphocytes and epithelial cells. While the glycoproteins required for entry into these two cell types differ, the gH/gL glycoprotein complex is essential for entry into both epithelial and B cells. Analysis of gH protein sequences from three gammaherpesviruses (EBV, marmoset, and rhesus) revealed a potential coiled-coil domain in the N terminus. Four leucines located in this region in EBV gH were replaced by alanines by site-directed mutagenesis and analyzed for cell-cell membrane fusion with B cells and epithelial cells. Reduction in fusion activity was observed for mutants containing L65A and/or L69A mutations, while substitutions in L55 and L74 enhanced the fusion activity of the mutant gH/gL complexes with both cell types. All of the mutants displayed levels of cell surface expression similar to those of wild-type gH and interacted with gL and gp42. The observation that a conservative mutation of leucine to alanine in the N terminus of EBV gH results in fusion-defective mutant gH/gL complexes is striking and points to an important role for this region in EBV-mediated membrane fusion with B lymphocytes and epithelial cells.
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Affiliation(s)
- Jasmina Omerović
- Department of Microbiology and Immunology, The Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
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24
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Abstract
This chapter describes the interactions between the different structural components of the viruses and discusses their relevance for the process of virion formation. Two key factors determine the efficiency of the assembly process: intracellular transport and molecular interactions. Many viruses have evolved elaborate strategies to ensure the swift and accurate delivery of the virion components to the cellular compartment(s) where they must meet and form (sub) structures. Assembly of viruses starts in the nucleus by the encapsidation of viral DNA, using cytoplasmically synthesized capsid proteins; nucleocapsids then migrate to the cytosol, by budding at the inner nuclear membrane followed by deenvelopment, to pick up the tegument proteins.
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Affiliation(s)
- Cornelis A M de Haan
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, 3584 CL Utrecht, The Netherlands
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25
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Song C, Micoli K, Hunter E. Activity of the Mason-Pfizer monkey virus fusion protein is modulated by single amino acids in the cytoplasmic tail. J Virol 2005; 79:11569-79. [PMID: 16140734 PMCID: PMC1212599 DOI: 10.1128/jvi.79.18.11569-11579.2005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mason-Pfizer monkey virus (M-PMV) encodes a transmembrane glycoprotein with a 38-amino-acid-long cytoplasmic tail. After the release of the immature virus, a viral protease-mediated cleavage of the cytoplasmic tail (CT) results in the loss of 17 amino acids from the carboxy terminus and renders the envelope protein fusion competent. To investigate the role of individual amino acid residues in the CT in fusion, a series of mutations was introduced, and the effects of these mutations on glycoprotein biosynthesis and fusion were examined. Most of the alanine-scanning mutations in the CT had little effect on fusion activity. However, four amino acid substitutions (threonine 4, lysine 7, glutamine 9, and isoleucine 10) resulted in substantially increased fusogenicity, while six (leucine 2, phenylalanine 5, isoleucine 13, lysine 16, proline 17, and glycine 31) resulted in much-reduced fusion. Interestingly, the bulk of these mutations are located upstream of the CT cleavage site in a region that has the potential to form a coiled-coil in the Env trimer. Substitutions at glutamine 9 and isoleucine 10 with alanine had the most dramatic positive effect and resulted in the formation of large syncytia. Taken together, these data demonstrate that individual residues within the cytoplasmic domain of M-PMV Env can modulate, in both a positive and negative manner, biological functions that are associated with the extracellular domains of the glycoprotein complex.
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Affiliation(s)
- Chisu Song
- Department of Microbiology, University of Alabama at Birmingham, 35294, USA
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26
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Guo Y, Sun S, Wang K, Zhang S, Zhu W, Chen Z. Elicitation of immunity in mice after immunization with the S2 subunit of the severe acute respiratory syndrome coronavirus. DNA Cell Biol 2005; 24:510-5. [PMID: 16101349 DOI: 10.1089/dna.2005.24.510] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The S2 domain of the severe acute respiratory syndrome coronavirus (SARS-CoV) spike (S) protein is responsible for fusion between virus and target cell membranes, and is expected to be immungenic. In this study, we investigated the immune responses against the S2 subunit in BALB/c mice, which were vaccinated either with plasmid DNA encoding the S2 domain (residues 681-1120), the recombinant S2 fragment (residues 681-980) in incomplete Freund's adjuvant, or with inactivated SARS-CoV. The increased number of specific cytotoxic cells (CTLs) and the high titer of specific antibody showed stimulation of both arms of the immune system in these groups. The shift in cytokines suggested that Th1-polarized immune response was induced by plasmid pCoVS2, meanwhile the Th2-dominant response was induced by recombinant S2 fragment and inactivated vaccine. However, the titer of neutralizing antibodies was only detectable in mice immunized with inactivated virus, but not with pCoVS2 plasmid. Taken together, the S2 domain could induce specific cellular immune response and a high level of total IgG but little neutralizing antibodies against infection by SARSCoV.
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Affiliation(s)
- Yingjun Guo
- Department of Medical Genetics, The Second Military Medical University, Shanghai, People's Republic of China
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27
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Duquerroy S, Vigouroux A, Rottier PJ, Rey FA, Jan Bosch B. Central ions and lateral asparagine/glutamine zippers stabilize the post-fusion hairpin conformation of the SARS coronavirus spike glycoprotein. Virology 2005; 335:276-85. [PMID: 15840526 PMCID: PMC7111771 DOI: 10.1016/j.virol.2005.02.022] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2005] [Revised: 02/02/2005] [Accepted: 02/22/2005] [Indexed: 10/27/2022]
Abstract
The coronavirus spike glycoprotein is a class I membrane fusion protein with two characteristic heptad repeat regions (HR1 and HR2) in its ectodomain. Here, we report the X-ray structure of a previously characterized HR1/HR2 complex of the severe acute respiratory syndrome coronavirus spike protein. As expected, the HR1 and HR2 segments are organized in antiparallel orientations within a rod-like molecule. The HR1 helices form an exceptionally long (120 A) internal coiled coil stabilized by hydrophobic and polar interactions. A striking arrangement of conserved asparagine and glutamine residues of HR1 propagates from two central chloride ions, providing hydrogen-bonding "zippers" that strongly constrain the path of the HR2 main chain, forcing it to adopt an extended conformation at either end of a short HR2 alpha-helix.
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Affiliation(s)
- Stéphane Duquerroy
- Laboratoire de Virologie Moléculaire and Structurale, UMR 2472/1157 CNRS-INRA and IFR 115, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Armelle Vigouroux
- Laboratoire de Virologie Moléculaire and Structurale, UMR 2472/1157 CNRS-INRA and IFR 115, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Peter J.M. Rottier
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine and Institute of Biomembranes, Utrecht University, 3584 CL Utrecht, The Netherlands
| | - Félix A. Rey
- Laboratoire de Virologie Moléculaire and Structurale, UMR 2472/1157 CNRS-INRA and IFR 115, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
- Corresponding author.
| | - Berend Jan Bosch
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine and Institute of Biomembranes, Utrecht University, 3584 CL Utrecht, The Netherlands
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28
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Nal B, Chan C, Kien F, Siu L, Tse J, Chu K, Kam J, Staropoli I, Crescenzo-Chaigne B, Escriou N, van der Werf S, Yuen KY, Altmeyer R. Differential maturation and subcellular localization of severe acute respiratory syndrome coronavirus surface proteins S, M and E. J Gen Virol 2005; 86:1423-1434. [PMID: 15831954 DOI: 10.1099/vir.0.80671-0] [Citation(s) in RCA: 174] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Post-translational modifications and correct subcellular localization of viral structural proteins are prerequisites for assembly and budding of enveloped viruses. Coronaviruses, like the severe acute respiratory syndrome-associated virus (SARS-CoV), bud from the endoplasmic reticulum-Golgi intermediate compartment. In this study, the subcellular distribution and maturation of SARS-CoV surface proteins S, M and E were analysed by using C-terminally tagged proteins. As early as 30 min post-entry into the endoplasmic reticulum, high-mannosylated S assembles into trimers prior to acquisition of complex N-glycans in the Golgi. Like S, M acquires high-mannose N-glycans that are subsequently modified into complex N-glycans in the Golgi. The N-glycosylation profile and the absence of O-glycosylation on M protein relate SARS-CoV to the previously described group 1 and 3 coronaviruses. Immunofluorescence analysis shows that S is detected in several compartments along the secretory pathway from the endoplasmic reticulum to the plasma membrane while M predominantly localizes in the Golgi, where it accumulates, and in trafficking vesicles. The E protein is not glycosylated. Pulse-chase labelling and confocal microscopy in the presence of protein translation inhibitor cycloheximide revealed that the E protein has a short half-life of 30 min. E protein is found in bright perinuclear patches colocalizing with endoplasmic reticulum markers. In conclusion, SARS-CoV surface proteins S, M and E show differential subcellular localizations when expressed alone suggesting that additional cellular or viral factors might be required for coordinated trafficking to the virus assembly site in the endoplasmic reticulum-Golgi intermediate compartment.
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Affiliation(s)
- Béatrice Nal
- HKU-Pasteur Research Centre, 8 Sassoon Road, Hong Kong, China
| | - Cheman Chan
- HKU-Pasteur Research Centre, 8 Sassoon Road, Hong Kong, China
| | - Francois Kien
- HKU-Pasteur Research Centre, 8 Sassoon Road, Hong Kong, China
| | - Lewis Siu
- HKU-Pasteur Research Centre, 8 Sassoon Road, Hong Kong, China
| | - Jane Tse
- HKU-Pasteur Research Centre, 8 Sassoon Road, Hong Kong, China
| | - Kid Chu
- HKU-Pasteur Research Centre, 8 Sassoon Road, Hong Kong, China
| | - Jason Kam
- HKU-Pasteur Research Centre, 8 Sassoon Road, Hong Kong, China
| | - Isabelle Staropoli
- Unité d'Immunologie Virale, Institut Pasteur, 25 rue du Dr Roux, Paris, France
| | | | - Nicolas Escriou
- Unité de Génétique Moléculaire des Virus Respiratoires, Institut Pasteur, 25 rue du Dr Roux, Paris, France
| | - Sylvie van der Werf
- Unité de Génétique Moléculaire des Virus Respiratoires, Institut Pasteur, 25 rue du Dr Roux, Paris, France
| | - Kwok-Yung Yuen
- Department of Microbiology, The University of Hong Kong, Hong Kong, China
| | - Ralf Altmeyer
- HKU-Pasteur Research Centre, 8 Sassoon Road, Hong Kong, China
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29
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Guillén J, Pérez-Berná AJ, Moreno MR, Villalaín J. Identification of the membrane-active regions of the severe acute respiratory syndrome coronavirus spike membrane glycoprotein using a 16/18-mer peptide scan: implications for the viral fusion mechanism. J Virol 2005; 79:1743-52. [PMID: 15650199 PMCID: PMC544113 DOI: 10.1128/jvi.79.3.1743-1752.2005] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2004] [Accepted: 09/16/2004] [Indexed: 02/07/2023] Open
Abstract
We have identified the membrane-active regions of the severe acute respiratory syndrome coronavirus (SARS CoV) spike glycoprotein by determining the effect on model membrane integrity of a 16/18-mer SARS CoV spike glycoprotein peptide library. By monitoring the effect of this peptide library on membrane leakage in model membranes, we have identified three regions on the SARS CoV spike glycoprotein with membrane-interacting capabilities: region 1, located immediately upstream of heptad repeat 1 (HR1) and suggested to be the fusion peptide; region 2, located between HR1 and HR2, which would be analogous to the loop domain of human immunodeficiency virus type 1; and region 3, which would correspond to the pretransmembrane region. The identification of these membrane-active regions, which are capable of modifying the biophysical properties of phospholipid membranes, supports their direct role in SARS CoV-mediated membrane fusion, as well as facilitating the future development of SARS CoV entry inhibitors.
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Affiliation(s)
- Jaime Guillén
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, E-03202 Elche-Alicante, Spain
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30
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Coronaviridae: a review of coronaviruses and toroviruses. CORONAVIRUSES WITH SPECIAL EMPHASIS ON FIRST INSIGHTS CONCERNING SARS 2005. [PMCID: PMC7123520 DOI: 10.1007/3-7643-7339-3_1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/22/2023]
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31
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Enjuanes L, Sola I, Alonso S, Escors D, Zúñiga S. Coronavirus reverse genetics and development of vectors for gene expression. Curr Top Microbiol Immunol 2005; 287:161-97. [PMID: 15609512 PMCID: PMC7120368 DOI: 10.1007/3-540-26765-4_6] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/23/2023]
Abstract
Knowledge of coronavirus replication, transcription, and virus-host interaction has been recently improved by engineering of coronavirus infectious cDNAs. With the transmissible gastroenteritis virus (TGEV) genome the efficient (>40 microg per 106 cells) and stable (>20 passages) expression of the foreign genes has been shown. Knowledge of the transcription mechanism in coronaviruses has been significantly increased, making possible the fine regulation of foreign gene expression. A new family of vectors based on single coronavirus genomes, in which essential genes have been deleted, has emerged including replication-competent, propagation-deficient vectors. Vector biosafety is being increased by relocating the RNA packaging signal to the position previously occupied by deleted essential genes, to prevent the rescue of fully competent viruses that might arise from recombination events with wild-type field coronaviruses. The large cloning capacity of coronaviruses (>5 kb) and the possibility of engineering the tissue and species tropism to target expression to different organs and animal species, including humans, has increased the potential of coronaviruses as vectors for vaccine development and, possibly, gene therapy.
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Affiliation(s)
- L Enjuanes
- Department of Molecular and Cell Biology, Centro Nacional de Biotecnología, CSIC, Campus Universidad Autónoma, 28049 Cantoblanco, Madrid, Spain.
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32
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Hsu CH, Ko TP, Yu HM, Tang TK, Chen ST, Wang AHJ. Immunological, structural, and preliminary X-ray diffraction characterizations of the fusion core of the SARS-coronavirus spike protein. Biochem Biophys Res Commun 2004; 324:761-7. [PMID: 15474492 PMCID: PMC7092949 DOI: 10.1016/j.bbrc.2004.09.116] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Indexed: 02/04/2023]
Abstract
The SARS-CoV spike protein, a glycoprotein essential for viral entry, is a primary target for vaccine and drug development. Two peptides denoted HR-N(SN50) and HR-C(SC40), corresponding to the Leu/Ile/Val-rich heptad-repeat regions from the N-terminal and C-terminal segments of the SARS-CoV spike S2 sequence, respectively, were synthesized and predicted to form trimeric assembly of hairpin-like structures. The polyclonal antibodies produced by recombinant S2 protein were tested for antigenicity of the two heptad repeats. We report here the first crystallographic study of the SARS spike HR-N/HR-C complex. The crystal belongs to the triclinic space group P1 and the data-set collected to 2.98 Å resolution showed noncrystallographic pseudo-222 and 3-fold symmetries. Based on these data, comparative modeling of the SARS-CoV fusion core was performed. The immunological and structural information presented herein may provide a more detailed understanding of the viral fusion mechanism as well as the development of effective therapy against SARS-CoV infection.
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Affiliation(s)
- Chun-Hua Hsu
- Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan, ROC
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33
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Song HC, Seo MY, Stadler K, Yoo BJ, Choo QL, Coates SR, Uematsu Y, Harada T, Greer CE, Polo JM, Pileri P, Eickmann M, Rappuoli R, Abrignani S, Houghton M, Han JH. Synthesis and characterization of a native, oligomeric form of recombinant severe acute respiratory syndrome coronavirus spike glycoprotein. J Virol 2004; 78:10328-35. [PMID: 15367599 PMCID: PMC516425 DOI: 10.1128/jvi.78.19.10328-10335.2004] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have expressed and characterized the severe acute respiratory syndrome coronavirus (SARS-CoV) spike protein in cDNA-transfected mammalian cells. The full-length spike protein (S) was newly synthesized as an endoglycosidase H (endo H)-sensitive glycoprotein (gp170) that is further modified into an endo H-resistant glycoprotein (gp180) in the Golgi apparatus. No substantial proteolytic cleavage of S was observed, suggesting that S is not processed into head (S1) and stalk (S2) domains as observed for certain other coronaviruses. While the expressed full-length S glycoprotein was exclusively cell associated, a truncation of S by excluding the C-terminal transmembrane and cytoplasmic tail domains resulted in the expression of an endoplasmic reticulum-localized glycoprotein (gp160) as well as a Golgi-specific form (gp170) which was ultimately secreted into the cell culture medium. Chemical cross-linking, thermal denaturation, and size fractionation analyses suggested that the full-length S glycoprotein of SARS-CoV forms a higher order structure of approximately 500 kDa, which is consistent with it being an S homotrimer. The latter was also observed in purified virions. The intracellular form of the C-terminally truncated S protein (but not the secreted form) also forms trimers, but with much less efficiency than full-length S. Deglycosylation of the full-length homotrimer with peptide N-glycosidase-F under native conditions abolished recognition of the protein by virus-neutralizing antisera raised against purified virions, suggesting the importance of the carbohydrate in the correct folding of the S protein. These data should aid in the design of recombinant vaccine antigens to prevent the spread of this emerging pathogen.
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MESH Headings
- Animals
- Antigens, Viral/chemistry
- Antigens, Viral/genetics
- Antigens, Viral/immunology
- Antigens, Viral/metabolism
- COS Cells
- Cell Line
- Chlorocebus aethiops
- Cricetinae
- Culture Media/chemistry
- DNA, Complementary
- DNA, Viral/genetics
- DNA, Viral/metabolism
- Endoplasmic Reticulum/chemistry
- Glycoside Hydrolases/metabolism
- Golgi Apparatus/chemistry
- Membrane Glycoproteins/chemistry
- Membrane Glycoproteins/genetics
- Membrane Glycoproteins/immunology
- Membrane Glycoproteins/metabolism
- Molecular Weight
- Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase/metabolism
- Protein Folding
- Protein Processing, Post-Translational
- Protein Structure, Tertiary
- Protein Subunits/analysis
- Protein Transport
- Recombinant Proteins/chemistry
- Recombinant Proteins/genetics
- Recombinant Proteins/immunology
- Recombinant Proteins/metabolism
- Severe acute respiratory syndrome-related coronavirus/genetics
- Spike Glycoprotein, Coronavirus
- Viral Envelope Proteins/chemistry
- Viral Envelope Proteins/genetics
- Viral Envelope Proteins/immunology
- Viral Envelope Proteins/metabolism
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Affiliation(s)
- Hyun Chul Song
- Vaccines Research, Chiron Corporation, 4560 Horton St., Emeryville, CA 94608, USA
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34
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Shen S, Law Y, Liu D. A single amino acid mutation in the spike protein of coronavirus infectious bronchitis virus hampers its maturation and incorporation into virions at the nonpermissive temperature. Virology 2004; 326:288-98. [PMID: 15302214 PMCID: PMC7126609 DOI: 10.1016/j.virol.2004.06.016] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2004] [Revised: 05/25/2004] [Accepted: 06/03/2004] [Indexed: 11/22/2022]
Abstract
The spike (S) glycoprotein of coronavirus is responsible for receptor binding and membrane fusion. A number of variants with deletions and mutations in the S protein have been isolated from naturally and persistently infected animals and tissue cultures. Here, we report the emergence and isolation of two temperature sensitive (ts) mutants and a revertant in the process of cold-adaptation of coronavirus infectious bronchitis virus (IBV) to a monkey kidney cell line. The complete sequences of wild type (wt) virus, two ts mutants, and the revertant were compared and variations linked to phenotypes were mapped. A single amino acid reversion (L294-to-Q) in the S protein is sufficient to abrogate the ts phenotype. Interestingly, unlike wt virus, the revertant grows well at and below 32 degrees C, the permissive temperature, as it carries other mutations in multiple genes that might be associated with the cold-adaptation phenotype. If the two ts mutants were allowed to enter cells at 32 degrees C, the S protein was synthesized, core-glycosylated and at least partially modified at 40 degrees C. However, compared with wt virus and the revertant, no infectious particles of these ts mutants were assembled and released from the ts mutant-infected cells at 40 degrees C. Evidence presented demonstrated that the Q294-to-L294 mutation, located at a highly conserved domain of the S1 subunit, might hamper processing of the S protein to a matured 180-kDa, endo-glycosidase H-resistant glycoprotein and the translocation of the protein to the cell surface. Consequently, some essential functions of the S protein, including mediation of cell-to-cell fusion and its incorporation into virions, were completely abolished.
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Affiliation(s)
| | | | - D.X Liu
- Corresponding author. Institute of Molecular and Cell Biology, 30 Medical Drive, 117609, Singapore. Fax: +65-67791117.
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35
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Sanchez-Morgado JM, Poynter S, Morris TH. Molecular characterization of a virulent canine coronavirus BGF strain. Virus Res 2004; 104:27-31. [PMID: 15177889 PMCID: PMC7114380 DOI: 10.1016/j.virusres.2004.02.038] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2003] [Revised: 02/22/2004] [Accepted: 02/24/2004] [Indexed: 10/31/2022]
Abstract
Molecular characterisation of a canine coronavirus (CCoV) isolate (BGF), associated with an outbreak of diarrhoea in puppies, showed 92.7% identity with attenuated Insavc-1 strain. Canine coronavirus BGF revealed a full length non-structural protein 3b (nsp 3b), associated with virulence in other coronaviruses, and a highly divergent region at the amino terminal domain of the membrane protein that may be implicated in avoiding the host immune reaction. This new canine coronavirus strain could help to identify virulence factors in coronavirus.
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36
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Xu Y, Liu Y, Lou Z, Qin L, Li X, Bai Z, Pang H, Tien P, Gao GF, Rao Z. Structural basis for coronavirus-mediated membrane fusion. Crystal structure of mouse hepatitis virus spike protein fusion core. J Biol Chem 2004; 279:30514-22. [PMID: 15123674 PMCID: PMC7982547 DOI: 10.1074/jbc.m403760200] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The surface transmembrane glycoprotein is responsible for mediating virion attachment to cell and subsequent virus-cell membrane fusion. However, the molecular mechanisms for the viral entry of coronaviruses remain poorly understood. The crystal structure of the fusion core of mouse hepatitis virus S protein, which represents the first fusion core structure of any coronavirus, reveals a central hydrophobic coiled coil trimer surrounded by three helices in an oblique, antiparallel manner. This structure shares significant similarity with both the low pH-induced conformation of influenza hemagglutinin and fusion core of HIV gp41, indicating that the structure represents a fusion-active state formed after several conformational changes. Our results also indicate that the mechanisms for the viral fusion of coronaviruses are similar to those of influenza virus and HIV. The coiled coil structure has unique features, which are different from other viral fusion cores. Highly conserved heptad repeat 1 (HR1) and HR2 regions in coronavirus spike proteins indicate a similar three-dimensional structure among these fusion cores and common mechanisms for the viral fusion. We have proposed the binding regions of HR1 and HR2 of other coronaviruses and a structure model of their fusion core based on our mouse hepatitis virus fusion core structure and sequence alignment. Drug discovery strategies aimed at inhibiting viral entry by blocking hairpin formation may be applied to the inhibition of a number of emerging infectious diseases, including severe acute respiratory syndrome.
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Affiliation(s)
- Yanhui Xu
- Laboratory of Structural Biology, Tsinghua University, Beijing 100084, China
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37
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Liu S, Xiao G, Chen Y, He Y, Niu J, Escalante CR, Xiong H, Farmar J, Debnath AK, Tien P, Jiang S. Interaction between heptad repeat 1 and 2 regions in spike protein of SARS-associated coronavirus: implications for virus fusogenic mechanism and identification of fusion inhibitors. Lancet 2004; 363:938-47. [PMID: 15043961 PMCID: PMC7140173 DOI: 10.1016/s0140-6736(04)15788-7] [Citation(s) in RCA: 397] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
BACKGROUND Studies on the fusion-inhibitory peptides derived from the heptad repeat 1 and 2 (HR1 and HR2) regions of the HIV-1 envelope glycoprotein gp41 provided crucial information on the viral fusogenic mechanism. We used a similar approach to study the fusogenic mechanism of severe-acute-respiratory-syndrome-associated coronavirus (SARS-CoV). METHODS We tested the inhibitory activity against infection of two sets of peptides corresponding to sequences of SARS-CoV spike protein HR1 and HR2 regions and investigated the interactions between the HR1 and HR2 peptides by surface plasmon resonance, sedimentation equilibration analysis, circular dichroism, native polyacrylamide-gel electrophoresis, size exclusion high-performance liquid chromatography, and computer-aided homology modelling and molecule docking analysis. FINDINGS One peptide, CP-1, derived from the HR2 region, inhibited SARS-CoV infection in the micromolar range. CP-1 bound with high affinity to a peptide from the HR1 region, NP-1. CP-1 alone had low alpha-helicity and self-associated to form a trimer in phosphate buffer (pH 7.2). CP-1 and NP-1 mixed in equimolar concentrations formed a six-helix bundle, similar to the fusogenic core structure of HIV-1 gp41. INTERPRETATION After binding to the target cell, the transmembrane spike protein might change conformation by association between the HR1 and HR2 regions to form an oligomeric structure, leading to fusion between the viral and target-cell membranes. At the prefusion intermediate state, CP-1 could bind to the HR1 region and interfere with the conformational changes, resulting in inhibition of SARS-CoV fusion with the target cells. CP-1 might be modifiable to increase its anti-SARS-CoV activity and could be further developed as an antiviral agent for treatment or prophylaxis of SARS-CoV infection.
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Affiliation(s)
- Shuwen Liu
- Lindsley F Kimball Research Institute, New York Blood Center, New York, NY, USA
| | - Gengfu Xiao
- Modern Virology Research Center, Wuhan University, Wuhan, China
| | - Yibang Chen
- Mount Sinai School of Medicine, New York, NY, USA
| | - Yuxian He
- Lindsley F Kimball Research Institute, New York Blood Center, New York, NY, USA
| | - Jinkui Niu
- Mount Sinai School of Medicine, New York, NY, USA
| | | | - Huabao Xiong
- Mount Sinai School of Medicine, New York, NY, USA
| | - James Farmar
- Lindsley F Kimball Research Institute, New York Blood Center, New York, NY, USA
| | - Asim K Debnath
- Lindsley F Kimball Research Institute, New York Blood Center, New York, NY, USA
| | - Po Tien
- Modern Virology Research Center, Wuhan University, Wuhan, China
| | - Shibo Jiang
- Lindsley F Kimball Research Institute, New York Blood Center, New York, NY, USA
- Correspondence to: Dr Shibo Jiang, Lindsley F Kimball Research Institute, New York Blood Center, 310 East 67th Street, New York, NY 10021, US
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38
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Tripet B, Howard MW, Jobling M, Holmes RK, Holmes KV, Hodges RS. Structural characterization of the SARS-coronavirus spike S fusion protein core. J Biol Chem 2004; 279:20836-49. [PMID: 14996844 PMCID: PMC8060857 DOI: 10.1074/jbc.m400759200] [Citation(s) in RCA: 164] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The spike (S) glycoprotein of coronaviruses mediates viral entry into host cells. It is a type 1 viral fusion protein that characteristically contains two heptad repeat regions, denoted HR-N and HR-C, that form coiled-coil structures within the ectodomain of the protein. Previous studies have shown that the two heptad repeat regions can undergo a conformational change from their native state to a 6-helix bundle (trimer of dimers), which mediates fusion of viral and host cell membranes. Here we describe the biophysical analysis of the two predicted heptad repeat regions within the severe acute respiratory syndrome coronavirus S protein. Our results show that in isolation the HR-N region forms a stable α-helical coiled coil that associates in a tetrameric state. The HR-C region in isolation formed a weakly stable trimeric coiled coil. When mixed together, the two peptide regions (HR-N and HR-C) associated to form a very stable α-helical 6-stranded structure (trimer of heterodimers). Systematic peptide mapping showed that the site of interaction between the HR-N and HR-C regions is between residues 916–950 of HR-N and residues 1151–1185 of HR-C. Additionally, interchain disulfide bridge experiments showed that the relative orientation of the HR-N and HR-C helices in the complex was antiparallel. Overall, the structure of the hetero-stranded complex is consistent with the structures observed for other type 1 viral fusion proteins in their fusion-competent state.
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Affiliation(s)
- Brian Tripet
- Department of Biochemistry and Molecular Genetics, University of Colorado Health Sciences Center, Denver, CO 80262, USA
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39
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Abstract
Sixty-one SARS coronavirus genomic sequences derived from the early, middle, and late phases of the severe acute respiratory syndrome (SARS) epidemic were analyzed together with two viral sequences from palm civets. Genotypes characteristic of each phase were discovered, and the earliest genotypes were similar to the animal SARS-like coronaviruses. Major deletions were observed in the Orf8 region of the genome, both at the start and the end of the epidemic. The neutral mutation rate of the viral genome was constant but the amino acid substitution rate of the coding sequences slowed during the course of the epidemic. The spike protein showed the strongest initial responses to positive selection pressures, followed by subsequent purifying selection and eventual stabilization.
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40
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Blaudez D, Kohler A, Martin F, Sanders D, Chalot M. Poplar metal tolerance protein 1 confers zinc tolerance and is an oligomeric vacuolar zinc transporter with an essential leucine zipper motif. THE PLANT CELL 2003; 15:2911-28. [PMID: 14630973 PMCID: PMC282827 DOI: 10.1105/tpc.017541] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2003] [Accepted: 09/18/2003] [Indexed: 05/18/2023]
Abstract
Cation diffusion facilitator (CDF) proteins are a recently discovered family of cation efflux transporters that might play an essential role in metal homeostasis and tolerance. Here, we describe the identification, characterization, and localization of PtdMTP1, a member of the CDF family from the hybrid poplar Populus trichocarpa x Populus deltoides. PtdMTP1 is expressed constitutively and ubiquitously, although at low levels. Heterologous expression in yeast showed that PtdMTP1 was able to complement the hypersensitivity of mutant strains to Zn but not to other metals, including Cd, Co, Mn, and Ni. PtdMTP1 fused to green fluorescent protein localized to the vacuolar membrane both in yeast and in plant cells, consistent with a function of PtdMTP1 in zinc sequestration. Overexpression of PtdMTP1 in Arabidopsis confers Zn tolerance. We show that PtdMTP1, when expressed in yeast and Arabidopsis, forms homooligomers, a novel feature of CDF members. Oligomer formation is disrupted by reducing agents, indicating possible disulfide bridge formation. PtdMTP1 also contains a conserved Leu zipper motif. Although not necessary for oligomer formation, Leu residues within this motif are required for PtdMTP1 functional activity.
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Affiliation(s)
- Damien Blaudez
- Biology Department, University of York, York YO10 5YW, United Kingdom
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41
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Tsai JC, Groot LD, Pinon JD, Iacono KT, Phillips JJ, Seo SH, Lavi E, Weiss SR. Amino acid substitutions within the heptad repeat domain 1 of murine coronavirus spike protein restrict viral antigen spread in the central nervous system. Virology 2003; 312:369-80. [PMID: 12919742 PMCID: PMC7125853 DOI: 10.1016/s0042-6822(03)00248-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Targeted recombination was carried out to select mouse hepatitis viruses (MHVs) in a defined genetic background, containing an MHV-JHM spike gene encoding either three heptad repeat 1 (HR1) substitutions (Q1067H, Q1094H, and L1114R) or L1114R alone. The recombinant virus, which expresses spike with the three substitutions, was nonfusogenic at neutral pH. Its replication was significantly inhibited by lysosomotropic agents, and it was highly neuroattenuated in vivo. In contrast, the recombinant expressing spike with L1114R alone mediated cell-to-cell fusion at neutral pH and replicated efficiently despite the presence of lysosomotropic agents; however, it still caused only subclinical morbidity and no mortality in animals. Thus, both recombinant viruses were highly attenuated and expressed viral antigen which was restricted to the olfactory bulbs and was markedly absent from other regions of the brains at 5 days postinfection. These data demonstrate that amino acid substitutions, in particular L1114R, within HR1 of the JHM spike reduced the ability of MHV to spread in the central nervous system. Furthermore, the requirements for low pH for fusion and viral entry are not prerequisites for the highly attenuated phenotype.
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Affiliation(s)
- Jean C Tsai
- Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6076, USA
| | - Linda de Groot
- Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6076, USA
| | - Josefina D Pinon
- Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6076, USA
| | - Kathryn T Iacono
- Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6076, USA
| | - Joanna J Phillips
- Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6076, USA
| | - Su-hun Seo
- Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6076, USA
| | - Ehud Lavi
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6076, USA
| | - Susan R Weiss
- Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6076, USA
- Corresponding author. Department of Microbiology, 203A Johnson Pavilion, University of Pennsylvania, Philadelphia, PA 19104-6076, USA. Fax: +1-215-573-4858.
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42
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Bosch BJ, van der Zee R, de Haan CAM, Rottier PJM. The coronavirus spike protein is a class I virus fusion protein: structural and functional characterization of the fusion core complex. J Virol 2003; 77:8801-11. [PMID: 12885899 PMCID: PMC167208 DOI: 10.1128/jvi.77.16.8801-8811.2003] [Citation(s) in RCA: 1037] [Impact Index Per Article: 49.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Coronavirus entry is mediated by the viral spike (S) glycoprotein. The 180-kDa oligomeric S protein of the murine coronavirus mouse hepatitis virus strain A59 is posttranslationally cleaved into an S1 receptor binding unit and an S2 membrane fusion unit. The latter is thought to contain an internal fusion peptide and has two 4,3 hydrophobic (heptad) repeat regions designated HR1 and HR2. HR2 is located close to the membrane anchor, and HR1 is some 170 amino acids (aa) upstream of it. Heptad repeat (HR) regions are found in fusion proteins of many different viruses and form an important characteristic of class I viral fusion proteins. We investigated the role of these regions in coronavirus membrane fusion. Peptides HR1 (96 aa) and HR2 (39 aa), corresponding to the HR1 and HR2 regions, were produced in Escherichia coli. When mixed together, the two peptides were found to assemble into an extremely stable oligomeric complex. Both on their own and within the complex, the peptides were highly alpha helical. Electron microscopic analysis of the complex revealed a rod-like structure approximately 14.5 nm in length. Limited proteolysis in combination with mass spectrometry indicated that HR1 and HR2 occur in the complex in an antiparallel fashion. In the native protein, such a conformation would bring the proposed fusion peptide, located in the N-terminal domain of HR1, and the transmembrane anchor into close proximity. Using biological assays, the HR2 peptide was shown to be a potent inhibitor of virus entry into the cell, as well as of cell-cell fusion. Both biochemical and functional data show that the coronavirus spike protein is a class I viral fusion protein.
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Affiliation(s)
- Berend Jan Bosch
- Virology Division, Department of Infectious Diseases and Immunity, Faculty of Veterinary Medicine, and Institute of Biomembranes, Utrecht University, 3584 CL Utrecht, The Netherlands
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43
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Casais R, Dove B, Cavanagh D, Britton P. Recombinant avian infectious bronchitis virus expressing a heterologous spike gene demonstrates that the spike protein is a determinant of cell tropism. J Virol 2003; 77:9084-9. [PMID: 12885925 PMCID: PMC167237 DOI: 10.1128/jvi.77.16.9084-9089.2003] [Citation(s) in RCA: 216] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2003] [Accepted: 05/19/2003] [Indexed: 12/11/2022] Open
Abstract
A recombinant infectious bronchitis virus (IBV), BeauR-M41(S), was generated using our reverse genetics system (R. Casais, V. Thiel, S. G. Siddell, D. Cavanagh, and P. Britton, J. Virol. 75:12359-12369, 2001), in which the ectodomain region of the spike gene from IBV M41-CK replaced the corresponding region of the IBV Beaudette genome. BeauR-M41(S) acquired the same cell tropism phenotype as IBV M41-CK in four different cell types, demonstrating that the IBV spike glycoprotein is a determinant of cell tropism.
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Affiliation(s)
- Rosa Casais
- Division of Molecular Biology, Institute for Animal Health, Compton Laboratory, Compton, Newbury, Berkshire RG20 7NN, United Kingdom
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44
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Abstract
Bcr-Abl is a dysregulated tyrosine kinase whose mechanism of activation is unclear. Here, we demonstrate that, like c-Abl, Bcr-Abl is negatively regulated through its SH3 domain. Kinase activity, transformation, and leukemogenesis by Bcr-Abl are greatly impaired by mutations of the Bcr coiled-coil domain that disrupt oligomerization, but restored by an SH3 point mutation that blocks ligand binding or a complementary mutation at the intramolecular SH3 binding site defined in c-Abl. Phosphorylation of tyrosines in the activation loop of the catalytic domain and the linker between the SH2 and catalytic domains (SH2-CD linker) is dependent on oligomerization and required for leukemogenesis. These results suggest that Bcr-Abl has a monomeric, unphosphorylated state with the SH3 domain engaged intramolecularly to Pro1124 in the SH2-CD linker, the form that is sensitive to the inhibitor imatinib (STI-571). The sole function of the coiled-coil domain is to disrupt the autoinhibited conformation through oligomerization and intermolecular autophosphorylation.
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MESH Headings
- 3T3 Cells
- Alanine/genetics
- Alanine/metabolism
- Amino Acid Sequence/genetics
- Animals
- Binding Sites/genetics
- Catalytic Domain/drug effects
- Catalytic Domain/genetics
- Cell Transformation, Neoplastic/genetics
- Cell Transformation, Neoplastic/metabolism
- Enzyme Inhibitors/pharmacology
- Eukaryotic Cells/enzymology
- Feedback, Physiological/drug effects
- Feedback, Physiological/genetics
- Fusion Proteins, bcr-abl
- Humans
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/enzymology
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/genetics
- Mice
- Mice, Inbred BALB C
- Models, Molecular
- Mutation/drug effects
- Mutation/genetics
- Phosphorylation/drug effects
- Proline/genetics
- Proline/metabolism
- Protein Binding/drug effects
- Protein Binding/genetics
- Protein Structure, Tertiary/drug effects
- Protein Structure, Tertiary/genetics
- Protein-Tyrosine Kinases/antagonists & inhibitors
- Protein-Tyrosine Kinases/genetics
- Protein-Tyrosine Kinases/metabolism
- Tyrosine/metabolism
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45
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Song C, Hunter E. Variable sensitivity to substitutions in the N-terminal heptad repeat of Mason-Pfizer monkey virus transmembrane protein. J Virol 2003; 77:7779-85. [PMID: 12829817 PMCID: PMC161947 DOI: 10.1128/jvi.77.14.7779-7785.2003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The transmembrane protein of Mason-Pfizer monkey virus contains two heptad repeats that are predicted to form amphipathic alpha-helices that mediate the conformational change necessary for membrane fusion. To analyze the relative sensitivity of the predicted hydrophobic face of the N-terminal heptad repeat to the insertion of uncharged, polar, and charged substitutions, mutations that introduced alanine, serine, or glutamic acid into positions 436, 443, 450, and 457 of the envelope protein were examined. Novel systems using Tat protein and the GHOST cell line were developed to test and quantitate the effects of the mutations on Env-mediated fusion and infectivity of the virus. While no single amino acid change at any of the positions interfered significantly with the synthesis, processing, or transport to the plasma membrane of glycoprotein complexes, 9 of the 12 nonconservative mutations in these residues completely abolished fusion activity and virus infectivity. Mutations in the central positions (443 and 450) of the heptad repeat region were the most detrimental to Env function, and even single alanine substitutions in these positions dramatically altered the fusogenicity of the protein. These results demonstrate that this N-terminal heptad repeat plays a critical role in Env-mediated membrane fusion and highlight the key function of central hydrophobic residues in this process and the sensitivity of all positions to charge substitutions.
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Affiliation(s)
- Chisu Song
- Department of Microbiology and Center for AIDS Research, University of Alabama at Birmingham, 845 19th Street S., Birmingham, AL 35294, USA
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46
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Jitrapakdee S, Unajak S, Sittidilokratna N, Hodgson RAJ, Cowley JA, Walker PJ, Panyim S, Boonsaeng V. Identification and analysis of gp116 and gp64 structural glycoproteins of yellow head nidovirus of Penaeus monodon shrimp. J Gen Virol 2003; 84:863-873. [PMID: 12655087 DOI: 10.1099/vir.0.18811-0] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Yellow head virus (YHV) is a major agent of disease in farmed penaeid shrimp. YHV virions purified from infected shrimp contain three major structural proteins of molecular mass 116 kDa (gp116), 64 kDa (gp64) and 20 kDa (p20). Two different staining methods indicated that the gp116 and gp64 proteins are glycosylated. Here we report the complete nucleotide sequence of ORF3, which encodes a polypeptide of 1666 amino acids with a calculated molecular mass of 185 713 Da (pI=6.68). Hydropathy analysis of the deduced ORF3 protein sequence identified six potential transmembrane helices and three ectodomains containing multiple sites for potential N-linked and O-linked glycosylation. N-terminal sequence analysis of mature gp116 and gp64 proteins indicated that each was derived from ORF3 by proteolytic cleavage of the polyprotein between residues Ala(228) and Thr(229), and Ala(1127) and Leu(1128), located at the C-terminal side of transmembrane helices 3 and 5, respectively. Comparison with the deduced ORF3 protein sequence of Australian gill-associated virus (GAV) indicated 83 % amino acid identity in gp64 and 71 % identity in gp116, which featured two significant sequence deletions near the N terminus. Database searches revealed no significant homology with other proteins. Recombinant gp64 expressed in E. coli with and without the C-terminal transmembrane region was shown to react with antibody raised against native gp64 purified from virions.
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Affiliation(s)
- Sarawut Jitrapakdee
- Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
- CENTEX Shrimp, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
| | - Sasimanas Unajak
- Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
- CENTEX Shrimp, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
| | - Nusra Sittidilokratna
- Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
- CENTEX Shrimp, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
| | - Richard A J Hodgson
- CSIRO Livestock Industries, Long Pocket Laboratories, Indooroopilly, Queensland, Australia
| | - Jeff A Cowley
- CSIRO Livestock Industries, Long Pocket Laboratories, Indooroopilly, Queensland, Australia
| | - Peter J Walker
- CSIRO Livestock Industries, Long Pocket Laboratories, Indooroopilly, Queensland, Australia
| | - Sakol Panyim
- Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
| | - Vichai Boonsaeng
- Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
- CENTEX Shrimp, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
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47
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Abstract
Membrane fusion, one of the most fundamental processes in life, occurs when two separate lipid membranes merge into a single continuous bilayer. Fusion reactions share common features, but are catalyzed by diverse proteins. These proteins mediate the initial recognition of the membranes that are destined for fusion and pull the membranes close together to destabilize the lipid/water interface and to initiate mixing of the lipids. A single fusion protein may do everything or assemblies of protein complexes may be required for intracellular fusion reactions to guarantee rigorous regulation in space and time. Cellular fusion machines are adapted to fit the needs of different reactions but operate by similar principles in order to achieve merging of the bilayers.
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Affiliation(s)
- Reinhard Jahn
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
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48
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Torres GE, Carneiro A, Seamans K, Fiorentini C, Sweeney A, Yao WD, Caron MG. Oligomerization and trafficking of the human dopamine transporter. Mutational analysis identifies critical domains important for the functional expression of the transporter. J Biol Chem 2003; 278:2731-9. [PMID: 12429746 DOI: 10.1074/jbc.m201926200] [Citation(s) in RCA: 204] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The dopamine transporter (DAT) is a presynaptic plasma membrane protein responsible for the termination of dopaminergic neurotransmission in the central nervous system. While most studies have focused on structure/function analysis, much less information is available regarding the assembly and the trafficking of this protein. To address this problem, we performed a mutational analysis of the DAT protein, combined with biochemical, immunological, and functional approaches. In mammalian cells co-expressing differentially tagged DAT molecules, HA-tagged DAT co-purified with 6His-tagged DAT demonstrating a physical interaction between transporter proteins. Evidence for the functional oligomerization of DAT was obtained using dominant-negative mutants of DAT. Two loss-of-function mutant transporters (Y335A and D79G) that were targeted to the cell surface inhibited wild-type DAT uptake activity without affecting the membrane targeting of the wild-type transporter. Moreover, non-functional amino and carboxyl termini-truncated mutants of DAT inhibited wild-type DAT function by interfering with the normal processing of the wild-type transporter to the cell membrane. Mutations in the leucine repeat of the second transmembrane domain of the transporter could eliminate the dominant-negative effect of all these mutants. In addition, a small fragment comprising the first two transmembrane domains of DAT inhibited wild-type transporter function but not when the leucine repeat motif was mutated. Taken together, our results suggest that the assembly of DAT monomers plays a critical role in the expression and function of the transporter.
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Affiliation(s)
- Gonzalo E Torres
- Howard Hughes Medical Institute, Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
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49
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Zelus BD, Schickli JH, Blau DM, Weiss SR, Holmes KV. Conformational changes in the spike glycoprotein of murine coronavirus are induced at 37 degrees C either by soluble murine CEACAM1 receptors or by pH 8. J Virol 2003; 77:830-40. [PMID: 12502799 PMCID: PMC140793 DOI: 10.1128/jvi.77.2.830-840.2003] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2002] [Accepted: 10/15/2002] [Indexed: 11/20/2022] Open
Abstract
The spike glycoprotein (S) of the murine coronavirus mouse hepatitis virus (MHV) binds to viral murine CEACAM receptor glycoproteins and causes membrane fusion. On virions, the 180-kDa S glycoprotein of the MHV-A59 strain can be cleaved by trypsin to form the 90-kDa N-terminal receptor-binding subunit (S1) and the 90-kDa membrane-anchored fusion subunit (S2). Incubation of virions with purified, soluble CEACAM1a receptor proteins at 37 degrees C and pH 6.5 neutralizes virus infectivity (B. D. Zelus, D. R. Wessner, R. K. Williams, M. N. Pensiero, F. T. Phibbs, M. deSouza, G. S. Dveksler, and K. V. Holmes, J. Virol. 72:7237-7244, 1998). We used liposome flotation and protease sensitivity assays to investigate the mechanism of receptor-induced, temperature-dependent virus neutralization. After incubation with soluble receptor at 37 degrees C and pH 6.5, virions became hydrophobic and bound to liposomes. Receptor binding induced a profound, apparently irreversible conformational change in S on the viral envelope that allowed S2, but not S1, to be degraded by trypsin at 4 degrees C. Various murine CEACAM proteins triggered conformational changes in S on recombinant MHV strains expressing S glycoproteins of MHV-A59 or MHV-4 (MHV-JHM) with the same specificities as seen for virus neutralization and virus-receptor activities. Increased hydrophobicity of virions and conformational change in S2 of MHV-A59 could also be induced by incubating virions at pH 8 and 37 degrees C, without soluble receptor. Surprisingly, the S protein of recombinant MHV-A59 virions with a mutation, H716D, that precluded cleavage between S1 and S2 could also be triggered to undergo a conformational change at 37 degrees C by soluble receptor at neutral pH or by pH 8 alone. A novel 120-kDa subunit was formed following incubation of the receptor-triggered S(A59)H716D virions with trypsin at 4 degrees C. The data show that unlike class 1 fusion glycoproteins of other enveloped viruses, the murine coronavirus S protein can be triggered to a membrane-binding conformation at 37 degrees C either by soluble receptor at neutral pH or by alkaline pH alone, without requiring previous activation by cleavage between S1 and S2.
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Affiliation(s)
- Bruce D Zelus
- Department of Microbiology, University of Colorado Health Sciences Center, Denver 80262, USA
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50
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Tsai JC, Zelus BD, Holmes KV, Weiss SR. The N-terminal domain of the murine coronavirus spike glycoprotein determines the CEACAM1 receptor specificity of the virus strain. J Virol 2003; 77:841-50. [PMID: 12502800 PMCID: PMC140794 DOI: 10.1128/jvi.77.2.841-850.2003] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Using isogenic recombinant murine coronaviruses expressing wild-type murine hepatitis virus strain 4 (MHV-4) or MHV-A59 spike glycoproteins or chimeric MHV-4/MHV-A59 spike glycoproteins, we have demonstrated the biological functionality of the N-terminus of the spike, encompassing the receptor binding domain (RBD). We have used two assays, one an in vitro liposome binding assay and the other a tissue culture replication assay. The liposome binding assay shows that interaction of the receptor with spikes on virions at 37 degrees C causes a conformational change that makes the virions hydrophobic so that they bind to liposomes (B. D. Zelus, J. H. Schickli, D. M. Blau, S. R. Weiss, and K. V. Holmes, J. Virol. 77: 830-840, 2003). Recombinant viruses with spikes containing the RBD of either MHV-A59 or MHV-4 readily associated with liposomes at 37 degrees C in the presence of soluble mCEACAM1(a), except for S(4)R, which expresses the entire wild-type MHV-4 spike and associated only inefficiently with liposomes following incubation with soluble mCEACAM1(a). In contrast, soluble mCEACAM1(b) allowed viruses with the MHV-A59 RBD to associate with liposomes more efficiently than did viruses with the MHV-4 RBD. In the second assay, which requires virus entry and replication, all recombinant viruses replicated efficiently in BHK cells expressing mCEACAM1(a). In BHK cells expressing mCEACAM1(b), only viruses expressing chimeric spikes with the MHV-A59 RBD could replicate, while replication of viruses expressing chimeric spikes with the MHV-4 RBD was undetectable. Despite having the MHV-4 RBD, S(4)R replicated in BHK cells expressing mCEACAM1(b); this is most probably due to spread via CEACAM1 receptor-independent cell-to-cell fusion, an activity displayed only by S(4)R among the recombinant viruses studied here. These data suggest that the RBD domain and the rest of the spike must coevolve to optimize function in viral entry and spread.
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Affiliation(s)
- Jean C Tsai
- Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia 19104, USA
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