title: Herpes simplex virus type 1 mediates fusion through a hemifusion intermediate by sequential activity of glycoproteins D, H, L, and B.
abstract: Virus-induced membrane fusion can be subdivided into three phases defined by studies of class I and class II fusion proteins. During Phase I, two membranes are brought into close apposition. Phase II marks the mixing of the outer membrane leaflets leading to formation of a hemifusion intermediate. A fusion pore stably forms and expands in Phase III, thereby completing the fusion process. Herpes simplex virus type 1 (HSV-1) requires four glycoproteins to complete membrane fusion, but none has been defined as class I or II. Therefore, we investigated whether HSV-1-induced membrane fusion occurred following the same general phases as those described for class I and II proteins. In this study we demonstrate that glycoprotein D (gD) and the glycoprotein H and glycoprotein L complex (gHL) mediated lipid mixing indicative of hemifusion. However, content mixing and full fusion required glycoprotein B (gB) to be present along with gD and gHL. Our results indicate that, like class I and II fusion proteins, fusion mediated by HSV-1 glycoproteins occurred through a hemifusion intermediate. In addition, both gB and gHL are probably directly involved in the fusion process. From this, we propose a sequential model for fusion via HSV-1 glycoproteins whereby gD is required for Phase I, gHL is required for Phase II, and gB is required for Phase III. We further propose that glycoprotein H and gB are likely to function sequentially to promote membrane fusion in other herpesviruses such as Epstein-Barr virus and human herpesvirus 8.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky, 800 Rose Street, Lexington, KY 40536, USA.
authors.forename: Ravi P
authors.initials: RP
authors.lastname: Subramanian
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Geraghty
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000494:pharmacology; D016466:CHO Cells; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D006023:Glycoproteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D018259:Herpesvirus 1, Human / Q000187:drug effects / Q000378:metabolism*; D050356:Lipid Metabolism / Q000187:drug effects; D008561:Membrane Fusion / Q000187:drug effects; D009154:Mutation / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014709:Vero Cells; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D000914:Antibodies, Viral; D006023:Glycoproteins; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D049452:Green Fluorescent Proteins