title: Steric accessibility of the HIV-1 gp41 N-trimer region.
abstract: During human immunodeficiency virus entry, gp41 undergoes a series of conformational changes that induce membrane fusion. Immediately prior to fusion, gp41 exists in a prehairpin intermediate in which the N- and C-peptide regions of gp41 are exposed. Rearrangement of this intermediate into a six-helix bundle composed of a trimeric coiled coil from the N-peptide region (N-trimer) surrounded by three peptides from the C-peptide region provides the driving force for membrane fusion, whereas prevention of six-helix bundle formation inhibits viral entry. Because of its central role in mediating viral entry, the N-trimer region of gp41 is a key vaccine target. Extensive efforts to discover potent and broadly neutralizing antibodies (Abs) against the N-trimer region have, thus far, been unsuccessful. In this study, we attached a potent C-peptide inhibitor that binds to the N-trimer region to cargo proteins of various sizes to examine the steric accessibility of the N-trimer during fusion. These inhibitors show a progressive loss of potency with increasing cargo size. Extension of the cargo/C-peptide linker partially restores inhibitory potency. These results demonstrate that the human immunodeficiency virus defends its critical hairpin-forming machinery by steric exclusion of large proteins and may explain the current dearth of neutralizing Abs against the N-trimer. In contrast, previous results suggest the C-peptide region is freely accessible during fusion, demonstrating that the N- and C-peptide regions are in structurally distinct environments. Based on these results, we also propose new strategies for the generation of neutralizing Abs that overcome this steric block.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Agnes E
authors.initials: AE
authors.lastname: Hamburger
authors.forename: Sunghwan
authors.initials: S
authors.lastname: Kim
authors.forename: Brett D
authors.initials: BD
authors.lastname: Welch
authors.forename: Michael S
authors.initials: MS
authors.lastname: Kay
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry; D002459:Cell Fusion; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015700:HIV Envelope Protein gp41 / Q000737:chemistry* / Q000502:physiology*; D006801:Humans; D020128:Inhibitory Concentration 50; D008954:Models, Biological; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry; D013237:Stereoisomerism; D020349:Surface Plasmon Resonance; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D000911:Antibodies, Monoclonal; D004791:Enzyme Inhibitors; D015700:HIV Envelope Protein gp41; D010455:Peptides; D011506:Proteins