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Structure-Function Dissection of Pseudorabies Virus Glycoprotein B Fusion Loops.

Authors
  • Vallbracht, Melina1
  • Brun, Delphine2, 3
  • Tassinari, Matteo2, 3
  • Vaney, Marie-Christine2, 3
  • Pehau-Arnaudet, Gérard4, 5
  • Guardado-Calvo, Pablo2, 3
  • Haouz, Ahmed5, 6
  • Klupp, Barbara G1
  • Mettenleiter, Thomas C1
  • Rey, Felix A2, 3
  • Backovic, Marija7, 3
  • 1 Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany. , (Germany)
  • 2 Institut Pasteur, Unité de Virologie Structurale, Département de Virologie, Paris, France. , (France)
  • 3 CNRS UMR3569, Paris, France. , (France)
  • 4 Institut Pasteur, Ultrapole, Département de Biologie Cellulaire et Infection, Paris, France. , (France)
  • 5 CNRS UMR3528, Paris, France. , (France)
  • 6 Institut Pasteur, Plate-Forme de Cristallographie, Paris, France. , (France)
  • 7 Institut Pasteur, Unité de Virologie Structurale, Département de Virologie, Paris, France [email protected] , (France)
Type
Published Article
Journal
Journal of Virology
Publisher
American Society for Microbiology
Publication Date
Jan 01, 2018
Volume
92
Issue
1
Identifiers
DOI: 10.1128/JVI.01203-17
PMID: 29046441
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Conserved across the family Herpesviridae, glycoprotein B (gB) is responsible for driving fusion of the viral envelope with the host cell membrane for entry upon receptor binding and activation by the viral gH/gL complex. Although crystal structures of the gB ectodomains of several herpesviruses have been reported, the membrane fusion mechanism has remained elusive. Here, we report the X-ray structure of the pseudorabies virus (PrV) gB ectodomain, revealing a typical class III postfusion trimer that binds membranes via its fusion loops (FLs) in a cholesterol-dependent manner. Mutagenesis of FL residues allowed us to dissect those interacting with distinct subregions of the lipid bilayer and their roles in membrane interactions. We tested 15 gB variants for the ability to bind to liposomes and further investigated a subset of them in functional assays. We found that PrV gB FL residues Trp187, Tyr192, Phe275, and Tyr276, which were essential for liposome binding and for fusion in cellular and viral contexts, form a continuous hydrophobic patch at the gB trimer surface. Together with results reported for other alphaherpesvirus gBs, our data suggest a model in which Phe275 from the tip of FL2 protrudes deeper into the hydrocarbon core of the lipid bilayer, while the side chains of Trp187, Tyr192, and Tyr276 form a rim that inserts into the more superficial interfacial region of the membrane to catalyze the fusion process. Comparative analysis with gBs from beta- and gamma-herpesviruses suggests that this membrane interaction model is valid for gBs from all herpesviruses.IMPORTANCE Herpesviruses are common human and animal pathogens that infect cells by entering via fusion of viral and cellular membranes. Central to the membrane fusion event is glycoprotein B (gB), which is the most conserved envelope protein across the herpesvirus family. Like other viral fusion proteins, gB anchors itself in the target membrane via two polypeptide segments called fusion loops (FLs). The molecular details of how gB FLs insert into the lipid bilayer have not been described. Here, we provide structural and functional data regarding key FL residues of gB from pseudorabies virus, a porcine herpesvirus of veterinary concern, which allows us to propose, for the first time, a molecular model to understand how the initial interactions by gBs from all herpesviruses with target membranes are established. Copyright © 2017 American Society for Microbiology.

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