title: Electrostatic Architecture of the Infectious Salmon Anemia Virus (ISAV) Core Fusion Protein Illustrates a Carboxyl-Carboxylate pH Sensor.
abstract: Segment 5, ORF 1 of the infectious salmon anemia virus (ISAV) genome, encodes for the ISAV F protein, which is responsible for viral-host endosomal membrane fusion during a productive ISAV infection. The entry machinery of ISAV is composed of a complex of the ISAV F and ISAV hemagglutinin esterase (HE) proteins in an unknown stoichiometry prior to receptor engagement by ISAV HE. Following binding of the receptor to ISAV HE, dissociation of the ISAV F protein from HE, and subsequent endocytosis, the ISAV F protein resolves into a fusion-competent oligomeric state. Here, we present a 2.1 Å crystal structure of the fusion core of the ISAV F protein determined at low pH. This structure has allowed us to unambiguously demonstrate that the ISAV entry machinery exhibits typical class I viral fusion protein architecture. Furthermore, we have determined stabilizing factors that accommodate the pH-dependent mode of ISAV transmission, and our structure has allowed the identification of a central coil that is conserved across numerous and varied post-fusion viral glycoprotein structures. We then discuss a mechanistic model of ISAV fusion that parallels the paramyxoviral class I fusion strategy wherein attachment and fusion are relegated to separate proteins in a similar fashion to ISAV fusion.
authors.affiliation: From the Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Cook
authors.affiliation: From the Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Hazel
authors.initials: H
authors.lastname: Soto-Montoya
authors.affiliation: From the Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Markus K
authors.initials: MK
authors.lastname: Korpela
authors.affiliation: From the Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada jeff.lee@utoronto.ca.
authors.forename: Jeffrey E
authors.initials: JE
authors.lastname: Lee
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D006389:Hemagglutinins, Viral / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D046829:Isavirus / Q000737:chemistry* / Q000235:genetics; D009976:Orthomyxoviridae Infections / Q000235:genetics / Q000378:metabolism / Q000821:virology*; D011487:Protein Conformation; D014760:Viral Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D053586:Virus Internalization
chemical_list: D006389:Hemagglutinins, Viral; D014760:Viral Fusion Proteins; C060814:hemagglutinin esterase
keywords: Class I viral fusion protein; ISAV; Isavirus; X-ray crystallography; animal virus; carboxyl-carboxylate; circular dichroism (CD); crystal structure; infectious salmon anemia virus; virus entry