Hepatitis C Virus Is Primed by CD81 Protein for Low pH-dependent Fusion*

• Type of Material: Article
• Authors: Nishi R. Sharma, Emory University; Guaniri Mateu, Université de Lyon; Marlene Dreux, Université de Lyon; Arash Grakoui, Emory University; Francois-Loic Cosset, Université de Lyon; Gregory Melikian, Emory University
• Language: English
• Date: 2011-09-02
• Publisher: American Society for Biochemistry and Molecular Biology
• Publication Version: Final Published Version
• Copyright Statement: © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.
• Final Published Version (URL): http://www.jbc.org/content/286/35/30361
• Title of Journal or Parent Work: Journal of Biological Chemistry
• Volume: 286
• Issue: 35
• Start Page: 30361
• End Page: 30376
• Grant/Funding Information: This work was supported, in whole or in part, by National Institutes of Health Grants DK083356 and AI070101 from USPHS (to A. G.).; This work was also supported by American Recovery and Reinvestment Act Grant R21 AI079714 (to G. M.), Agence Nationale pour la Recherche Contre le SIDA et les Hépatites Virales, and European Research Council Grant ERC-2008-AdG-233130-HEPCENT (to F.-L. C.).; A.G. supported by Yerkes Research Center Base Grant RR-00165.
• Keywords: Hepatitis Virus; Endocytosis; Membrane Fusion; Viral Protein; Fusion Protein; Virus Entry; Receptor-mediated Conformational Changes
• Research Categories: Chemistry, Biochemistry; Biology, Virology

Abstract

Hepatitis C virus (HCV) entry into permissive cells is a complex process that involves interactions with at least four co-factors followed by endocytosis and low pH-dependent fusion with endosomes. The precise sequence of receptor engagement and their roles in promoting HCV E1E2 glycoprotein-mediated fusion are poorly characterized. Because cell-free HCV tolerates an acidic environment, we hypothesized that binding to one or more receptors on the cell surface renders E1E2 competent to undergo low pH-induced conformational changes and promote fusion with endosomes. To test this hypothesis, we examined the effects of low pH and of the second extracellular loop (ECL2) of CD81, one of the four entry factors, on HCV infectivity. Pretreatment with an acidic buffer or with ECL2 enhanced infection through changing the E1E2 conformation, as evidenced by the altered reactivity of these proteins with conformation-specific antibodies and stable association with liposomes. However, neither of the two treatments alone permitted direct fusion with the cell plasma membrane. Sequential HCV preincubation with ECL2 and acidic buffer in the absence of target cells resulted in a marked loss of infectivity, implying that the receptor-bound HCV is primed for low pH-dependent conformational changes. Indeed, soluble receptor-pretreated HCV fused with the cell plasma membrane at low pH under conditions blocking an endocytic entry pathway. These findings suggest that CD81 primes HCV for low pH-dependent fusion early in the entry process. The simple triggering paradigm and intermediate conformations of E1E2 identified in this study could help guide future vaccine and therapeutic efforts to block HCV infection.