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An D, Li Z, Beavis AC, Briggs KR, Harvill M, He B. Cleavage of the syncytial protein of J paramyxovirus is required for its ability to promote cell-cell fusion. Proc Natl Acad Sci U S A 2024; 121:e2403389121. [PMID: 38833471 PMCID: PMC11181024 DOI: 10.1073/pnas.2403389121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2024] [Accepted: 05/02/2024] [Indexed: 06/06/2024] Open
Abstract
Cell-cell fusion mediated by most paramyxovirus requires fusion protein (F) and attachment protein (H, HN, or G). The F protein is proteolytic cleaved to be fusogenically active. J paramyxovirus (JPV) has a unique feature in the family Paramyxoviridae: It encodes an integral membrane protein, syncytial protein (SP, formerly known as transmembrane protein, TM), which is essential in JPV-promoted cell-cell fusion (i.e., syncytial). In this study, we report that cleavage of SP is essential for its syncytial-promoting activity. We have identified the cleavage site of SP at amino acid residues 172 to 175, LKTG, and deletion of the "LKTG" residues abolished SP protein cleavage and its ability to promote cell-cell fusion. Replacing the cleavage site LKTG with a factor Xa protease cleavage site allows cleavage of the SP with factor Xa protease and restores its ability to promote cell-cell fusion. Furthermore, results from a hemifusion assay indicate that cleavage of SP plays an important role in the progression from the intermediate hemifusion state to a complete fusion. This work indicates that SP has many characteristics of a fusion protein. We propose that SP is likely a cell-cell fusion-promoting protein.
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Affiliation(s)
- Dong An
- Department of Infectious Diseases, University of Georgia College of Veterinary Medicine, Athens, GA30602
| | - Zhuo Li
- Department of Infectious Diseases, University of Georgia College of Veterinary Medicine, Athens, GA30602
| | - Ashley C. Beavis
- Department of Infectious Diseases, University of Georgia College of Veterinary Medicine, Athens, GA30602
| | - Kelsey R. Briggs
- Department of Infectious Diseases, University of Georgia College of Veterinary Medicine, Athens, GA30602
| | - Mason Harvill
- Department of Infectious Diseases, University of Georgia College of Veterinary Medicine, Athens, GA30602
| | - Biao He
- Department of Infectious Diseases, University of Georgia College of Veterinary Medicine, Athens, GA30602
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2
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Tomé-Poderti L, Olivero-Deibe N, Carrión F, Portela MM, Obal G, Cabrera G, Bianchi S, Lima A, Addiego A, Durán R, Moratorio G, Pritsch O. Characterization and application of recombinant Bovine Leukemia Virus Env protein. Sci Rep 2024; 14:12190. [PMID: 38806566 PMCID: PMC11133380 DOI: 10.1038/s41598-024-62811-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2024] [Accepted: 05/21/2024] [Indexed: 05/30/2024] Open
Abstract
The Bovine Leukemia Virus (BLV) Envelope (Env) glycoprotein complex is instrumental in viral infectivity and shapes the host's immune response. This study presents the production and characterization of a soluble furin-mutated BLV Env ectodomain (sBLV-EnvFm) expressed in a stable S2 insect cell line. We purified a 63 kDa soluble protein, corresponding to the monomeric sBLV-EnvFm, which predominantly presented oligomannose and paucimannose N-glycans, with a high content of core fucose structures. Our results demonstrate that our recombinant protein can be recognized from specific antibodies in BLV infected cattle, suggesting its potential as a powerful diagnostic tool. Moreover, the robust humoral immune response it elicited in mice shows its potential contribution to the development of subunit-based vaccines against BLV.
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Affiliation(s)
- Lorena Tomé-Poderti
- Immunovirology Lab, Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay.
- Morphogenesis and Antigenicity of HIV and Hepatitis Viruses (MAVIVH), INSERM Unit 1259, Université de Tours and CHRU de Tours, Tours, France.
| | | | - Federico Carrión
- Immunovirology Lab, Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
| | - María Magdalena Portela
- Analytical Biochemistry and Proteomics Unit, Instituto de Investigaciones Biológicas Clemente Estable/Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
- Facultad de Ciencias, Universidad de la República, 11400, Montevideo, Uruguay
| | - Gonzalo Obal
- Immunovirology Lab, Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
| | - Gleysin Cabrera
- Analytical Biochemistry and Proteomics Unit, Instituto de Investigaciones Biológicas Clemente Estable/Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
| | - Sergio Bianchi
- Laboratory of Molecular Biomarkers, Department of Physiopathology, University Hospital, Universidad de la República, 11600, Montevideo, Uruguay
- Functional Genomics Unit, Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
| | - Analia Lima
- Analytical Biochemistry and Proteomics Unit, Instituto de Investigaciones Biológicas Clemente Estable/Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
| | - Andrés Addiego
- Immunovirology Lab, Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
| | - Rosario Durán
- Analytical Biochemistry and Proteomics Unit, Instituto de Investigaciones Biológicas Clemente Estable/Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
| | - Gonzalo Moratorio
- Experimental Evolution of Viruses, Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
- Laboratorio de Virología Molecular, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Otto Pritsch
- Immunovirology Lab, Institut Pasteur de Montevideo, 11400, Montevideo, Uruguay
- Immunobiology Department School of Medicine, Universidad de la República, 11800, Montevideo, Uruguay
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3
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Chen P, Chen M, Menon A, Hussain AI, Carey E, Lee C, Horwitz J, O'Connell S, Cooper JW, Schwartz R, Gowetski DB. Development of a High Yielding Bioprocess for a Pre-fusion RSV Subunit Vaccine. J Biotechnol 2020; 325:261-270. [PMID: 33068697 DOI: 10.1016/j.jbiotec.2020.10.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 09/22/2020] [Accepted: 10/12/2020] [Indexed: 02/03/2023]
Abstract
Respiratory syncytial virus (RSV) is a highly contagious virus causing severe infection in infants and the elderly. Various approaches are being used to develop an effective RSV vaccine. The RSV fusion (F) subunit, particularly the cleaved trimeric pre-fusion F, is one of the most promising vaccine candidates under development. The pre-fusion conformation elicits the majority of neutralizing antibodies during natural infection. However, this pre-fusion conformation is metastable and prone to conversion to a post-fusion conformation, thus hindering the potential of this construct as a vaccine antigen. The Vaccine Research Center (VRC) at the National Institutes of Health (NIH) designed a structurally stabilized pre-fusion F glycoprotein, DS-Cav1, that showed high immunogenicity and induced a neutralizing response in animal studies. To advance this candidate to clinical manufacturing, a production process that maintained product quality (i.e. a cleaved trimer with pre-fusion conformation) and delivered high protein expression levels was required. This report describes the development of the vaccine candidate including vector design and cell culture process development to meet these challenges. Co-transfection of individual plasmids to express DS-Cav1 and furin (for DS-Cav1 cleavage and activation) demonstrated a superior protein product expression and pre-fusion conformation compared to co-expression with a double gene vector. A top clone was selected based on these measurements. Protein expression levels were further increased by seeding density optimization and a biphasic hypothermia temperature downshift. The combined efforts led to a high-yield fed-batch production of approximately 1,500 mg/L (or up to 15,000 doses per liter) at harvest. The process was scaled up and demonstrated to be reproducible at 50 L-scale for toxicity and Phase I clinical trial use. Preliminary phase I data indicate the pre-fusion antigen has a promising efficacy (Crank et al., 2019).
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Affiliation(s)
- Peifeng Chen
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA.
| | - Mingzhong Chen
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
| | - Amritha Menon
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
| | - Althaf I Hussain
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
| | - Elizabeth Carey
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
| | - Christopher Lee
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
| | - Joe Horwitz
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
| | - Sarah O'Connell
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
| | - Johnathan W Cooper
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
| | - Richard Schwartz
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
| | - Daniel B Gowetski
- Vaccine Production Program, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9 West Watkins Mill Rd., Gaithersburg, MD, 20878, USA
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4
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Kanai Y, Kawagishi T, Sakai Y, Nouda R, Shimojima M, Saijo M, Matsuura Y, Kobayashi T. Cell-cell fusion induced by reovirus FAST proteins enhances replication and pathogenicity of non-enveloped dsRNA viruses. PLoS Pathog 2019; 15:e1007675. [PMID: 31022290 PMCID: PMC6504114 DOI: 10.1371/journal.ppat.1007675] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2018] [Revised: 05/07/2019] [Accepted: 03/03/2019] [Indexed: 12/13/2022] Open
Abstract
Fusogenic reoviruses encode fusion-associated small transmembrane (FAST) protein, which induces cell-cell fusion. FAST protein is the only known fusogenic protein in non-enveloped viruses, and its role in virus replication is not yet known. We generated replication-competent, FAST protein-deficient pteropine orthoreovirus and demonstrated that FAST protein was not essential for viral replication, but enhanced viral replication in the early phase of infection. Addition of recombinant FAST protein enhanced replication of FAST-deficient virus and other non-fusogenic viruses in a fusion-dependent and FAST-species-independent manner. In a mouse model, replication and pathogenicity of FAST-deficient virus were severely impaired relative to wild-type virus, indicating that FAST protein is a major determinant of the high pathogenicity of fusogenic reovirus. FAST-deficient virus also conferred effective protection against challenge with lethal homologous virus strains in mice. Our results demonstrate a novel role of a viral fusogenic protein and the existence of a cell-cell fusion-dependent replication system in non-enveloped viruses.
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Affiliation(s)
- Yuta Kanai
- Department of Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
| | - Takahiro Kawagishi
- Department of Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
| | - Yusuke Sakai
- Laboratory of Veterinary Pathology, Joint Faculty of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan
| | - Ryotaro Nouda
- Department of Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
| | - Masayuki Shimojima
- Department of Virology I, National Institute of Infectious Diseases, Tokyo, Japan
| | - Masayuki Saijo
- Department of Virology I, National Institute of Infectious Diseases, Tokyo, Japan
| | - Yoshiharu Matsuura
- Department of Molecular Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
| | - Takeshi Kobayashi
- Department of Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
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5
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Structural, antigenic and immunogenic features of respiratory syncytial virus glycoproteins relevant for vaccine development. Vaccine 2016; 35:461-468. [PMID: 27692522 DOI: 10.1016/j.vaccine.2016.09.045] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Accepted: 09/22/2016] [Indexed: 11/22/2022]
Abstract
Extraordinary progress in the structure and immunobiology of the human respiratory syncytial virus glycoproteins has been accomplished during the last few years. Determination of the fusion (F) glycoprotein structure folded in either the prefusion or the postfusion conformation was an inspiring breakthrough not only to understand the structural changes associated with the membrane fusion process but additionally to appreciate the antigenic intricacies of the F protein. Furthermore, these developments have opened new avenues for structure-based designs of promising hRSV vaccine candidates. Finally, recent advances in our knowledge of the attachment (G) glycoprotein and its interaction with cell-surface receptors have revitalized interest in this molecule as a vaccine, as well as its role in hRSV immunobiology.
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6
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Trisaccharide containing α2,3-linked sialic acid is a receptor for mumps virus. Proc Natl Acad Sci U S A 2016; 113:11579-11584. [PMID: 27671656 DOI: 10.1073/pnas.1608383113] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mumps virus (MuV) remains an important pathogen worldwide, causing epidemic parotitis, orchitis, meningitis, and encephalitis. Here we show that MuV preferentially uses a trisaccharide containing α2,3-linked sialic acid in unbranched sugar chains as a receptor. Crystal structures of the MuV attachment protein hemagglutinin-neuraminidase (MuV-HN) alone and in complex with the α2,3-sialylated trisaccharide revealed that in addition to the interaction between the MuV-HN active site residues and sialic acid, other residues, including an aromatic residue, stabilize the third sugar of the trisaccharide. The importance of the aromatic residue and the third sugar in the MuV-HN-receptor interaction was confirmed by computational energy calculations, isothermal titration calorimetry studies, and glycan-binding assays. Furthermore, MuV-HN was found to bind more efficiently to unbranched α2,3-sialylated sugar chains compared with branched ones. Importantly, the strategically located aromatic residue is conserved among the HN proteins of sialic acid-using paramyxoviruses, and alanine substitution compromised their ability to support cell-cell fusion. These results suggest that not only the terminal sialic acid but also the adjacent sugar moiety contribute to receptor function for mumps and these paramyxoviruses. The distribution of structurally different sialylated glycans in tissues and organs may explain in part MuV's distinct tropism to glandular tissues and the central nervous system. In the crystal structure, the epitopes for neutralizing antibodies are located around the α-helices of MuV-HN that are not well conserved in amino acid sequences among different genotypes of MuV. This may explain the fact that MuV reinfection sometimes occurs.
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7
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Más V, Rodriguez L, Olmedillas E, Cano O, Palomo C, Terrón MC, Luque D, Melero JA, McLellan JS. Engineering, Structure and Immunogenicity of the Human Metapneumovirus F Protein in the Postfusion Conformation. PLoS Pathog 2016; 12:e1005859. [PMID: 27611367 PMCID: PMC5017722 DOI: 10.1371/journal.ppat.1005859] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2016] [Accepted: 08/10/2016] [Indexed: 12/03/2022] Open
Abstract
Human metapneumovirus (hMPV) is a paramyxovirus that is a common cause of bronchiolitis and pneumonia in children less than five years of age. The hMPV fusion (F) glycoprotein is the primary target of neutralizing antibodies and is thus a critical vaccine antigen. To facilitate structure-based vaccine design, we stabilized the ectodomain of the hMPV F protein in the postfusion conformation and determined its structure to a resolution of 3.3 Å by X-ray crystallography. The structure resembles an elongated cone and is very similar to the postfusion F protein from the related human respiratory syncytial virus (hRSV). In contrast, significant differences were apparent with the postfusion F proteins from other paramyxoviruses, such as human parainfluenza type 3 (hPIV3) and Newcastle disease virus (NDV). The high similarity of hMPV and hRSV postfusion F in two antigenic sites targeted by neutralizing antibodies prompted us to test for antibody cross-reactivity. The widely used monoclonal antibody 101F, which binds to antigenic site IV of hRSV F, was found to cross-react with hMPV postfusion F and neutralize both hRSV and hMPV. Despite the cross-reactivity of 101F and the reported cross-reactivity of two other antibodies, 54G10 and MPE8, we found no detectable cross-reactivity in the polyclonal antibody responses raised in mice against the postfusion forms of either hMPV or hRSV F. The postfusion-stabilized hMPV F protein did, however, elicit high titers of hMPV-neutralizing activity, suggesting that it could serve as an effective subunit vaccine. Structural insights from these studies should be useful for designing novel immunogens able to induce wider cross-reactive antibody responses.
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MESH Headings
- Amino Acid Sequence
- Animals
- Antibodies, Monoclonal/immunology
- Antibodies, Neutralizing/immunology
- Antibodies, Viral/immunology
- Antigens, Viral/chemistry
- Antigens, Viral/genetics
- Antigens, Viral/immunology
- Cross Reactions
- Crystallography, X-Ray
- Female
- Genetic Engineering
- Humans
- Metapneumovirus/genetics
- Metapneumovirus/immunology
- Mice
- Mice, Inbred BALB C
- Models, Molecular
- Molecular Conformation
- Respiratory Syncytial Virus, Human/genetics
- Respiratory Syncytial Virus, Human/immunology
- Sequence Alignment
- Viral Fusion Proteins/chemistry
- Viral Fusion Proteins/genetics
- Viral Fusion Proteins/immunology
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Affiliation(s)
- Vicente Más
- Unidad de Biología Viral, Centro Nacional de Microbiología and CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Laura Rodriguez
- Unidad de Biología Viral, Centro Nacional de Microbiología and CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Eduardo Olmedillas
- Unidad de Biología Viral, Centro Nacional de Microbiología and CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Olga Cano
- Unidad de Biología Viral, Centro Nacional de Microbiología and CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Concepción Palomo
- Unidad de Biología Viral, Centro Nacional de Microbiología and CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - María C. Terrón
- Unidad de Microscopía Electrónica y Confocal, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Daniel Luque
- Unidad de Microscopía Electrónica y Confocal, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - José A. Melero
- Unidad de Biología Viral, Centro Nacional de Microbiología and CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Jason S. McLellan
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America
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8
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Bose S, Jardetzky TS, Lamb RA. Timing is everything: Fine-tuned molecular machines orchestrate paramyxovirus entry. Virology 2015; 479-480:518-31. [PMID: 25771804 PMCID: PMC4424121 DOI: 10.1016/j.virol.2015.02.037] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Revised: 01/21/2015] [Accepted: 02/18/2015] [Indexed: 11/30/2022]
Abstract
The Paramyxoviridae include some of the great and ubiquitous disease-causing viruses of humans and animals. In most paramyxoviruses, two viral membrane glycoproteins, fusion protein (F) and receptor binding protein (HN, H or G) mediate a concerted process of recognition of host cell surface molecules followed by fusion of viral and cellular membranes, resulting in viral nucleocapsid entry into the cytoplasm. The interactions between the F and HN, H or G viral glycoproteins and host molecules are critical in determining host range, virulence and spread of these viruses. Recently, atomic structures, together with biochemical and biophysical studies, have provided major insights into how these two viral glycoproteins successfully interact with host receptors on cellular membranes and initiate the membrane fusion process to gain entry into cells. These studies highlight the conserved core mechanisms of paramyxovirus entry that provide the fundamental basis for rational anti-viral drug design and vaccine development. New structural and functional insights into paramyxovirus entry mechanisms. Current data on paramyxovirus glycoproteins suggest a core conserved entry mechanism. Diverse mechanisms preventing premature fusion activation exist in these viruses. Precise spacio-temporal interplay between paramyxovirus glycoproteins initiate entry.
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Affiliation(s)
- Sayantan Bose
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208-3500, United States.
| | - Theodore S Jardetzky
- Department of Structural Biology and Program in Immunology, Stanford University School of Medicine, Stanford, CA 94305, United States
| | - Robert A Lamb
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208-3500, United States; Howard Hughes Medical Institute, Northwestern University, Evanston, IL 60208-3500, United States.
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9
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Palomo C, Mas V, Vázquez M, Cano O, Luque D, Terrón MC, Calder LJ, Melero JA. Polyclonal and monoclonal antibodies specific for the six-helix bundle of the human respiratory syncytial virus fusion glycoprotein as probes of the protein post-fusion conformation. Virology 2014; 460-461:119-27. [PMID: 25010277 DOI: 10.1016/j.virol.2014.05.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Revised: 03/28/2014] [Accepted: 05/01/2014] [Indexed: 12/01/2022]
Abstract
Human respiratory syncytial virus (hRSV) has two major surface glycoproteins (G and F) anchored in the lipid envelope. Membrane fusion promoted by hRSV_F occurs via refolding from a pre-fusion form to a highly stable post-fusion state involving large conformational changes of the F trimer. One of these changes results in assembly of two heptad repeat sequences (HRA and HRB) into a six-helix bundle (6HB) motif. To assist in distinguishing pre- and post-fusion conformations of hRSV_F, we have prepared polyclonal (α-6HB) and monoclonal (R145) rabbit antibodies specific for the 6HB. Among other applications, these antibodies were used to explore the requirements of 6HB formation by isolated protein segments or peptides and by truncated mutants of the F protein. Site-directed mutagenesis and electron microscopy located the R145 epitope in the post-fusion hRSV_F at a site distantly located from previously mapped epitopes, extending the repertoire of antibodies that can decorate the F molecule.
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Affiliation(s)
- Concepción Palomo
- Unidad de Biología Viral, Centro Nacional de Microbiología, Madrid, Spain; CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
| | - Vicente Mas
- Unidad de Biología Viral, Centro Nacional de Microbiología, Madrid, Spain; CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
| | - Mónica Vázquez
- Unidad de Biología Viral, Centro Nacional de Microbiología, Madrid, Spain; CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
| | - Olga Cano
- Unidad de Biología Viral, Centro Nacional de Microbiología, Madrid, Spain; CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
| | - Daniel Luque
- Unidad de Microscopía Electrónica y Confocal, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
| | - María C Terrón
- Unidad de Microscopía Electrónica y Confocal, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
| | - Lesley J Calder
- National Institute for Medical Research, MRC, Mill Hill, London NW7 1AA, UK
| | - José A Melero
- Unidad de Biología Viral, Centro Nacional de Microbiología, Madrid, Spain; CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain.
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10
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Detection of respiratory syncytial virus fusion protein variants between 2009 and 2012 in China. Arch Virol 2013; 159:1089-98. [PMID: 24297488 DOI: 10.1007/s00705-013-1870-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Accepted: 09/23/2013] [Indexed: 10/26/2022]
Abstract
Respiratory syncytial virus (RSV) causes respiratory tract infection, particularly acute lower respiratory tract infection (ALRTI), in early childhood. The RSV fusion protein (F protein) is an important surface protein, and it is the target of both cytotoxic T lymphocytes (CTL) and neutralizing antibodies; thus, it may be useful as a candidate for vaccine research. This study investigated the genetic diversity of the RSV F protein. To this end, a total of 1800 nasopharyngeal aspirates from hospitalized children with ALRTI were collected for virus isolation between June 2009 and March 2012. There were 333 RSV-positive cases (277 cases of RSV A, 55 of RSV B, and 1 with both RSV A and RSV B), accounting for 18.5 % of the total cases. Next, 130 clinical strains (107 of RSV A, 23 of RSV B) were selected for F gene sequencing. Phylogenetic analysis revealed that the F gene sequence is highly conserved, with significant amino acid changes at residues 16, 25, 45, 102, 122, 124, 209, and 447. Mutations in human histocompatibility leukocyte antigen (HLA)-restricted CTL epitopes were also observed. Variations in RSV A F protein at the palivizumab binding site 276 (N→S) increased between 2009 and 2012 and became predominant. Western blot analysis and microneutralization data showed a substitution at residue 276 (N→S) in RSV A that did not cause resistance to palivizumab. In conclusion, the RSV F gene is geographically and temporally conserved, but limited genetic variations were still observed. These data could be helpful for the development of vaccines against RSV infection.
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11
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The respiratory syncytial virus fusion protein and neutrophils mediate the airway mucin response to pathogenic respiratory syncytial virus infection. J Virol 2013; 87:10070-82. [PMID: 23843644 DOI: 10.1128/jvi.01347-13] [Citation(s) in RCA: 80] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Respiratory syncytial virus (RSV) is the leading cause of death due to a viral etiology in infants. RSV disease is characterized by epithelial desquamation, neutrophilic bronchiolitis and pneumonia, and obstructive pulmonary mucus. It has been shown that infection of BALB/cJ mice with RSV clinical isolate A2001/2-20 (2-20) results in a higher early viral load, greater airway necrosis, and higher levels of interleukin-13 (IL-13) and airway mucin expression than infection with RSV laboratory strain A2. We hypothesized that the fusion (F) protein of RSV 2-20 is a mucus-inducing viral factor. In vitro, the fusion activity of 2-20 F but not that of A2 F was enhanced by expression of RSV G. We generated a recombinant F-chimeric RSV by replacing the F gene of A2 with the F gene of 2-20, generating A2-2-20F. Similar to the results obtained with the parent 2-20 strain, infection of BALB/cJ mice with A2-2-20F resulted in a higher early viral load and higher levels of subsequent pulmonary mucin expression than infection with the A2 strain. A2-2-20F infection induced greater necrotic airway damage and neutrophil infiltration than A2 infection. We hypothesized that the neutrophil response to A2-2-20F infection is involved in mucin expression. Antibody-mediated depletion of neutrophils in RSV-infected mice resulted in lower tumor necrosis factor alpha levels, fewer IL-13-expressing CD4 T cells, and less airway mucin production in the lung. Our data are consistent with a model in which the F and attachment (G) glycoprotein functional interaction leads to enhanced fusion and F is a key factor in airway epithelium infection, pathogenesis, and subsequent airway mucin expression.
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12
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Nipah virus envelope-pseudotyped lentiviruses efficiently target ephrinB2-positive stem cell populations in vitro and bypass the liver sink when administered in vivo. J Virol 2012. [PMID: 23192877 DOI: 10.1128/jvi.02032-12] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Sophisticated retargeting systems for lentiviral vectors have been developed in recent years. Most seek to suppress the viral envelope's natural tropism while modifying the receptor-binding domain such that its tropism is determined by the specificity of the engineered ligand-binding motif. Here we took advantage of the natural tropism of Nipah virus (NiV), whose attachment envelope glycoprotein has picomolar affinity for ephrinB2, a molecule proposed as a molecular marker of "stemness" (present on embryonic, hematopoietic, and neural stem cells) as well as being implicated in tumorigenesis of specific cancers. NiV entry requires both the fusion (F) and attachment (G) glycoproteins. Truncation of the NiV-F cytoplasmic tail (T5F) alone, combined with full-length NiV-G, resulted in optimal titers of NiV-pseudotyped particles (NiVpp) (∼10(6) IU/ml), even without ultracentrifugation. To further enhance the infectivity of NiVpp, we engineered a hyperfusogenic NiV-F protein lacking an N-linked glycosylation site (T5FΔN3). T5FΔN3/wt G particles exhibited enhanced infectivity on less permissive cell lines and efficiently targeted ephrinB2(+) cells even in a 1,000-fold excess of ephrinB2-negative cells, all without any loss of specificity, as entry was abrogated by soluble ephrinB2. NiVpp also transduced human embryonic, hematopoietic, and neural stem cell populations in an ephrinB2-dependent manner. Finally, intravenous administration of the luciferase reporter NiVpp-T5FΔN3/G to mice resulted in signals being detected in the spleen and lung but not in the liver. Bypassing the liver sink is a critical barrier for targeted gene therapy. The extraordinary specificity of NiV-G for ephrinB2 holds promise for targeting specific ephrinB2(+) populations in vivo or in vitro.
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13
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Chang A, Dutch RE. Paramyxovirus fusion and entry: multiple paths to a common end. Viruses 2012; 4:613-36. [PMID: 22590688 PMCID: PMC3347325 DOI: 10.3390/v4040613] [Citation(s) in RCA: 145] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Revised: 03/10/2012] [Accepted: 04/12/2012] [Indexed: 12/24/2022] Open
Abstract
The paramyxovirus family contains many common human pathogenic viruses, including measles, mumps, the parainfluenza viruses, respiratory syncytial virus, human metapneumovirus, and the zoonotic henipaviruses, Hendra and Nipah. While the expression of a type 1 fusion protein and a type 2 attachment protein is common to all paramyxoviruses, there is considerable variation in viral attachment, the activation and triggering of the fusion protein, and the process of viral entry. In this review, we discuss recent advances in the understanding of paramyxovirus F protein-mediated membrane fusion, an essential process in viral infectivity. We also review the role of the other surface glycoproteins in receptor binding and viral entry, and the implications for viral infection. Throughout, we concentrate on the commonalities and differences in fusion triggering and viral entry among the members of the family. Finally, we highlight key unanswered questions and how further studies can identify novel targets for the development of therapeutic treatments against these human pathogens.
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Affiliation(s)
| | - Rebecca E. Dutch
- Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, KY 40536, USA
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14
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Abstract
The proprotein convertases (PCs) are secretory mammalian serine proteinases related to bacterial subtilisin-like enzymes. The family of PCs comprises nine members, PC1/3, PC2, furin, PC4, PC5/6, PACE4, PC7, SKI-1/S1P, and PCSK9 (Fig. 3.1). While the first seven PCs cleave after single or paired basic residues, the last two cleave at non-basic residues and the last one PCSK9 only cleaves one substrate, itself, for its activation. The targets and substrates of these convertases are very varied covering many aspects of cellular biology and communication. While it took more than 22 years to begin to identify the first member in 1989-1990, in less than 14 years they were all characterized. So where are we 20 years later in 2011? We have now reached a level of maturity needed to begin to unravel the mechanisms behind the complex physiological functions of these PCs both in health and disease states. We are still far away from comprehensively understanding the various ramifications of their roles and to identify their physiological substrates unequivocally. How do these enzymes function in vivo? Are there other partners to be identified that would modulate their activity and/or cellular localization? Would non-toxic inhibitors/silencers of some PCs provide alternative therapies to control some pathologies and improve human health? Are there human SNPs or mutations in these PCs that correlate with disease, and can these help define the finesses of their functions and/or cellular sorting? The more we know about a given field, the more questions will arise, until we are convinced that we have cornered the important angles. And yet the future may well reserve for us many surprises that may allow new leaps in our understanding of the fascinating biology of these phylogenetically ancient eukaryotic proteases (Fig. 3.2) implicated in health and disease, which traffic through the cells via multiple sorting pathways (Fig. 3.3).
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Affiliation(s)
- Nabil G Seidah
- Biochemical Neuroendocrinology Laboratory, Clinical Research Institute of Montreal, Montreal, QC, Canada H2W 1R7.
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15
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Abstract
Nipah (NiV) and Hendra (HeV) viruses cause cell-cell fusion (syncytia) in brain, lung, heart, and kidney tissues, leading to encephalitis, pneumonia, and often death. Membrane fusion is essential to both viral entry and virus-induced cell-cell fusion, a hallmark of henipavirus infections. Elucidiation of the mechanism(s) of membrane fusion is critical to understanding henipavirus pathobiology and has the potential to identify novel strategies for the development of antiviral therapeutic agents. Henipavirus membrane fusion requires the coordinated actions of the viral attachment (G) and fusion (F) glycoproteins. Current henipavirus fusion models posit that attachment of NiV or HeV G to its cell surface receptors releases F from its metastable pre-fusion conformation to mediate membrane fusion. The identification of ephrinB2 and ephrinB3 as henipavirus receptors has paved the way for recent advances in our understanding of henipavirus membrane fusion. These advances highlight mechanistic similarities and differences between membrane fusion for the henipavirus and other genera within the Paramyxoviridae family. Here, we review these mechanisms and the current gaps in our knowledge in the field.
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Affiliation(s)
- Hector C Aguilar
- Department of Veterinary Microbiology and Pathology, Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-7010, USA.
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16
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Collins PL, Melero JA. Progress in understanding and controlling respiratory syncytial virus: still crazy after all these years. Virus Res 2011; 162:80-99. [PMID: 21963675 PMCID: PMC3221877 DOI: 10.1016/j.virusres.2011.09.020] [Citation(s) in RCA: 338] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2011] [Revised: 09/13/2011] [Accepted: 09/14/2011] [Indexed: 01/25/2023]
Abstract
Human respiratory syncytial virus (RSV) is a ubiquitous pathogen that infects everyone worldwide early in life and is a leading cause of severe lower respiratory tract disease in the pediatric population as well as in the elderly and in profoundly immunosuppressed individuals. RSV is an enveloped, nonsegmented negative-sense RNA virus that is classified in Family Paramyxoviridae and is one of its more complex members. Although the replicative cycle of RSV follows the general pattern of the Paramyxoviridae, it encodes additional proteins. Two of these (NS1 and NS2) inhibit the host type I and type III interferon (IFN) responses, among other functions, and another gene encodes two novel RNA synthesis factors (M2-1 and M2-2). The attachment (G) glycoprotein also exhibits unusual features, such as high sequence variability, extensive glycosylation, cytokine mimicry, and a shed form that helps the virus evade neutralizing antibodies. RSV is notable for being able to efficiently infect early in life, with the peak of hospitalization at 2-3 months of age. It also is notable for the ability to reinfect symptomatically throughout life without need for significant antigenic change, although immunity from prior infection reduces disease. It is widely thought that re-infection is due to an ability of RSV to inhibit or subvert the host immune response. Mechanisms of viral pathogenesis remain controversial. RSV is notable for a historic, tragic pediatric vaccine failure involving a formalin-inactivated virus preparation that was evaluated in the 1960s and that was poorly protective and paradoxically primed for enhanced RSV disease. RSV also is notable for the development of a successful strategy for passive immunoprophylaxis of high-risk infants using RSV-neutralizing antibodies. Vaccines and new antiviral drugs are in pre-clinical and clinical development, but controlling RSV remains a formidable challenge.
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MESH Headings
- Aged
- Aged, 80 and over
- Antibodies, Neutralizing/administration & dosage
- Antibodies, Neutralizing/immunology
- Antibodies, Viral/genetics
- Antibodies, Viral/immunology
- Antigens, Viral/genetics
- Antigens, Viral/immunology
- Antiviral Agents/administration & dosage
- Child
- Communicable Disease Control/organization & administration
- Cytokines/immunology
- Humans
- Immunity, Innate
- Infant
- RNA, Viral/genetics
- RNA, Viral/immunology
- Respiratory Syncytial Virus Infections/drug therapy
- Respiratory Syncytial Virus Infections/immunology
- Respiratory Syncytial Virus Infections/prevention & control
- Respiratory Syncytial Virus Infections/virology
- Respiratory Syncytial Virus Vaccines/administration & dosage
- Respiratory Syncytial Virus, Human/genetics
- Respiratory Syncytial Virus, Human/immunology
- Vaccination
- Vaccines, Attenuated/administration & dosage
- Viral Proteins/chemistry
- Viral Proteins/genetics
- Viral Proteins/immunology
- Virus Replication/genetics
- Virus Replication/immunology
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Affiliation(s)
- Peter L. Collins
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - José A. Melero
- Centro Nacional de Microbiología and CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Majadahonda, 28220 Madrid, Spain
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Residues of the human metapneumovirus fusion (F) protein critical for its strain-related fusion phenotype: implications for the virus replication cycle. J Virol 2011; 85:12650-61. [PMID: 21937649 DOI: 10.1128/jvi.05485-11] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The paramyxovirus F protein promotes fusion of the viral and cell membranes for virus entry, as well as cell-cell fusion for syncytium formation. Most paramyxovirus F proteins are triggered at neutral pH to initiate membrane fusion. Previous studies, however, demonstrated that human metapneumovirus (hMPV) F proteins are triggered at neutral or acidic pH in transfected cells, depending on the strain origin of the F sequences (S. Herfst et al., J. Virol. 82:8891-8895, 2008). We now report an extensive mutational analysis which identifies four variable residues (294, 296, 396, and 404) as the main determinants of the different syncytial phenotypes found among hMPV F proteins. These residues lie near two conserved histidines (H368 and H435) in a three-dimensional (3D) model of the pretriggered hMPV F trimer. Mutagenesis of H368 and H435 indicates that protonation of these histidines (particularly His435) is a key event to destabilize the hMPV F proteins that require low pH for cell-cell fusion. The syncytial phenotypes were reproduced in cells infected with the corresponding hMPV strains. However, the low-pH dependency for syncytium formation could not be related with a virus entry pathway dependent on an acidic environment. It is postulated that low pH may be acting for some hMPV strains as certain destabilizing mutations found in unusual strains of other paramyxoviruses. In any case, the results presented here and those reported by Schowalter et al. (J. Virol. 83:1511-1522, 2009) highlight the relevance of certain residues in the linker region and domain II of the pretriggered hMPV F protein for the process of membrane fusion.
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18
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Infection of lymphoblastoid cell lines by Kaposi's sarcoma-associated herpesvirus: critical role of cell-associated virus. J Virol 2011; 85:9767-77. [PMID: 21795352 DOI: 10.1128/jvi.05136-11] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV) displays strong lymphotropism in vivo, but paradoxically, established B cell lines have largely been refractory to infection by soluble KSHV virions. Here we show that this block can be overcome by exposure to cell-associated virus. Doxycycline-inducible recombinant KSHV.219 (rKSHV.219)-harboring SLK (iSLK.219) cells were employed as KSHV donors. Cocultivation of lymphoid cell lines with reactivated iSLK.219 cells resulted in readily demonstrable viral entry into each cell line; similar observations were made in primary tonsillar B cell cultures. Moreover, infected lymphoid cells were able to outgrow upon puromycin selection, indicating development of persistent infection. Infected BJAB cells display signatures of latent infection, including classical latency-associated transcripts, a punctate pattern of LANA expression, and episomal maintenance of the KSHV genome. However, when lytically activated by various chemical stimuli, infected BJAB cells were able to produce only low levels of infectious virions. These data demonstrate that (i) cell-associated viruses can bypass viral entry blocks in most lymphoid cell lines, (ii) the determinants of cell-associated virus entry differ from those of soluble virion infection, and (iii) immortalized lymphoblastoid lines have partial postentry blocks to efficient lytic reactivation.
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19
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Recombinant Sendai viruses expressing fusion proteins with two furin cleavage sites mimic the syncytial and receptor-independent infection properties of respiratory syncytial virus. J Virol 2011; 85:2771-80. [PMID: 21228237 DOI: 10.1128/jvi.02065-10] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cell entry by paramyxoviruses requires fusion between viral and cellular membranes. Paramyxovirus infection also gives rise to the formation of multinuclear, fused cells (syncytia). Both types of fusion are mediated by the viral fusion (F) protein, which requires proteolytic processing at a basic cleavage site in order to be active for fusion. In common with most paramyxoviruses, fusion mediated by Sendai virus F protein (F(SeV)) requires coexpression of the homologous attachment (hemagglutinin-neuraminidase [HN]) protein, which binds to cell surface sialic acid receptors. In contrast, respiratory syncytial virus fusion protein (F(RSV)) is capable of fusing membranes in the absence of the viral attachment (G) protein. Moreover, F(RSV) is unique among paramyxovirus fusion proteins since F(RSV) possesses two multibasic cleavage sites, which are separated by an intervening region of 27 amino acids. We have previously shown that insertion of both F(RSV) cleavage sites in F(SeV) decreases dependency on the HN attachment protein for syncytium formation in transfected cells. We now describe recombinant Sendai viruses (rSeV) that express mutant F proteins containing one or both F(RSV) cleavage sites. All cleavage-site mutant viruses displayed reduced thermostability, with double-cleavage-site mutants exhibiting a hyperfusogenic phenotype in infected cells. Furthermore, insertion of both F(RSV) cleavage sites in F(SeV) reduced dependency on the interaction of HN with sialic acid for infection, thus mimicking the unique ability of RSV to fuse and infect cells in the absence of a separate attachment protein.
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20
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Side chain packing below the fusion peptide strongly modulates triggering of the Hendra virus F protein. J Virol 2010; 84:10928-32. [PMID: 20702638 DOI: 10.1128/jvi.01108-10] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Triggering of the Hendra virus fusion (F) protein is required to initiate the conformational changes which drive membrane fusion, but the factors which control triggering remain poorly understood. Mutation of a histidine predicted to lie near the fusion peptide to alanine greatly reduced fusion despite wild-type cell surface expression levels, while asparagine substitution resulted in a moderate restoration in fusion levels. Slowed kinetics of six-helix bundle formation, as judged by sensitivity to heptad repeat B-derived peptides, was observed for all H372 mutants. These data suggest that side chain packing beneath the fusion peptide is an important regulator of Hendra virus F triggering.
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21
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Smith EC, Popa A, Chang A, Masante C, Dutch RE. Viral entry mechanisms: the increasing diversity of paramyxovirus entry. FEBS J 2010; 276:7217-27. [PMID: 19878307 DOI: 10.1111/j.1742-4658.2009.07401.x] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The paramyxovirus family contains established human pathogens such as the measles virus and human respiratory syncytial virus, as well as emerging pathogens including the Hendra and Nipah viruses and the recently identified human metapneumovirus. Two major envelope glycoproteins, the attachment protein and the fusion protein, promote the processes of viral attachment and virus-cell membrane fusion required for entry. Although common mechanisms of fusion protein proteolytic activation and the mechanism of membrane fusion promotion have been shown in recent years, considerable diversity exists in the family relating to receptor binding and the potential mechanisms of fusion triggering.
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Affiliation(s)
- Everett C Smith
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, KY 40536-0509, USA
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22
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Belouzard S, Chu VC, Whittaker GR. Activation of the SARS coronavirus spike protein via sequential proteolytic cleavage at two distinct sites. Proc Natl Acad Sci U S A 2009; 106:5871-6. [PMID: 19321428 PMCID: PMC2660061 DOI: 10.1073/pnas.0809524106] [Citation(s) in RCA: 749] [Impact Index Per Article: 49.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2008] [Indexed: 11/18/2022] Open
Abstract
The coronavirus spike protein (S) plays a key role in the early steps of viral infection, with the S1 domain responsible for receptor binding and the S2 domain mediating membrane fusion. In some cases, the S protein is proteolytically cleaved at the S1-S2 boundary. In the case of the severe acute respiratory syndrome coronavirus (SARS-CoV), it has been shown that virus entry requires the endosomal protease cathepsin L; however, it was also found that infection of SARS-CoV could be strongly induced by trypsin treatment. Overall, in terms of how cleavage might activate membrane fusion, proteolytic processing of the SARS-CoV S protein remains unclear. Here, we identify a proteolytic cleavage site within the SARS-CoV S2 domain (S2', R797). Mutation of R797 specifically inhibited trypsin-dependent fusion in both cell-cell fusion and pseudovirion entry assays. We also introduced a furin cleavage site at both the S2' cleavage site within S2 793-KPTKR-797 (S2'), as well as at the junction of S1 and S2. Introduction of a furin cleavage site at the S2' position allowed trypsin-independent cell-cell fusion, which was strongly increased by the presence of a second furin cleavage site at the S1-S2 position. Taken together, these data suggest a novel priming mechanism for a viral fusion protein, with a critical proteolytic cleavage event on the SARS-CoV S protein at position 797 (S2'), acting in concert with the S1-S2 cleavage site to mediate membrane fusion and virus infectivity.
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Affiliation(s)
- Sandrine Belouzard
- Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853
| | - Victor C. Chu
- Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853
| | - Gary R. Whittaker
- Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853
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23
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de Graaf M, Schrauwen EJA, Herfst S, van Amerongen G, Osterhaus ADME, Fouchier RAM. Fusion protein is the main determinant of metapneumovirus host tropism. J Gen Virol 2009; 90:1408-1416. [PMID: 19264630 DOI: 10.1099/vir.0.009688-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Human metapneumovirus (HMPV) and avian metapneumovirus subgroup C (AMPV-C) infect humans and birds, respectively. This study confirmed the difference in host range in turkey poults, and analysed the contribution of the individual metapneumovirus genes to host range in an in vitro cell-culture model. Mammalian Vero-118 cells supported replication of both HMPV and AMPV-C in contrast to avian quail fibroblast (QT6) cells in which only AMPV-C replicated to high titres. Inoculation of Vero-118 and QT6 cells with recombinant HMPV in which genes were exchanged with those of AMPV-C revealed that the metapneumovirus fusion (F) protein is the main determinant for host tropism. Chimeric viruses in which polymerase complex proteins were exchanged between HMPV and AMPV-C replicated less efficiently compared with HMPV in QT6 cells. Using mini-genome systems, it was shown that exchanging these polymerase proteins resulted in reduced replication and transcription efficiency in QT6 cells. Examination of infected Vero-118 and QT6 cells revealed that viruses containing the F protein of AMPV-C yielded larger syncytia compared with viruses containing the HMPV F protein. Cell-content mixing assays revealed that the F protein of AMPV-C was more fusogenic compared with the F protein of HMPV, and that the F2 region is responsible for the difference observed between AMPV-C and HMPV F-promoted fusion in QT6 and Vero-118 cells. This study provides insight into the determinants of host tropism and membrane fusion of metapneumoviruses.
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Affiliation(s)
- Miranda de Graaf
- Department of Virology, Erasmus Medical Centre, PO Box 2040, 3000 CA Rotterdam, The Netherlands
| | - Eefje J A Schrauwen
- Department of Virology, Erasmus Medical Centre, PO Box 2040, 3000 CA Rotterdam, The Netherlands
| | - Sander Herfst
- Department of Virology, Erasmus Medical Centre, PO Box 2040, 3000 CA Rotterdam, The Netherlands
| | - Geert van Amerongen
- Department of Virology, Erasmus Medical Centre, PO Box 2040, 3000 CA Rotterdam, The Netherlands
| | - Albert D M E Osterhaus
- Department of Virology, Erasmus Medical Centre, PO Box 2040, 3000 CA Rotterdam, The Netherlands
| | - Ron A M Fouchier
- Department of Virology, Erasmus Medical Centre, PO Box 2040, 3000 CA Rotterdam, The Netherlands
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