title: The prefusogenic intermediate of HIV-1 gp41 contains exposed C-peptide regions.
abstract: The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein is composed of a complex between the surface subunit gp120, which binds to cellular receptors, and the transmembrane subunit gp41. Upon activation of the envelope glycoprotein by cellular receptors, gp41 undergoes conformational changes that mediate fusion of the viral and cellular membranes. Prior to formation of a fusogenic "trimer-of-hairpins" structure, gp41 transiently adopts a prefusogenic conformation whose structural features are poorly understood. An important approach toward understanding structural conformations of gp41 during HIV-1 entry has been to analyze the structural targets of gp41 inhibitors. We have constructed epitope-tagged versions of 5-Helix, a designed protein that binds to the C-peptide region of gp41 and inhibits HIV-1 membrane fusion. Using these 5-Helix variants, we examined which conformation of gp41 is the target of 5-Helix. We find that although 5-Helix binds poorly to native gp41, it binds strongly to gp41 activated by interaction of the envelope protein with either soluble CD4 or membrane-bound cellular receptors. This preferential interaction with activated gp41 results in the accumulation of 5-Helix on the surface of activated cells. These results strongly suggest that the gp41 prefusogenic intermediate is the target of 5-Helix and that this intermediate has a remarkably "open" structure, with exposed C-peptide regions. These results provide important structural information about this intermediate that should facilitate the development of HIV-1 entry inhibitors and may lead to new vaccine strategies.
authors.affiliation: Division of Biology, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Takumi
authors.initials: T
authors.lastname: Koshiba
authors.forename: David C
authors.initials: DC
authors.lastname: Chan
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D015704:CD4 Antigens / Q000096:biosynthesis; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002942:Circular Dichroism; D003001:Cloning, Molecular; D000939:Epitopes; D004926:Escherichia coli / Q000378:metabolism; D015700:HIV Envelope Protein gp41 / Q000378:metabolism*; D006801:Humans; D008561:Membrane Fusion; D051379:Mice; D008954:Models, Biological; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010455:Peptides / Q000737:chemistry; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013053:Spectrophotometry
chemical_list: D015704:CD4 Antigens; D000939:Epitopes; D015700:HIV Envelope Protein gp41; D010455:Peptides