Antibody Epitopes Sensitive to the State of Human Immunodeficiency Virus Type 1 gp41 Oligomerization Map to a Putative α-Helical Region

Abstract

Two antibodies, affinity-purified from human immunodeficiency virus-positive human plasma with synthetic peptides in the region gp41(566–596), were found to recognize oligomeric gp41 more strongly than the monomeric form in an immunoblot assay. In contrast, a murine anti-gp160 monoclonal antibody, which maps within this sequence to gp41(581–596), recognized only monomeric gp41 after disruption of the oligomer with sodium dodecyl sulfate. This monoclonal anti-gp160 antibody did not recognize chemically crosslinked oligomeric gp41 that had been treated with similar conditions used to disrupt the gp41 oligomer. These results indicate that this epitope is inaccessible to binding by this antibody when gp41 is oligomeric. Cyanogen bromide cleavage of gp41 resulted in a 17-kD fragment Thr-541-Met-631. A significant proportion of this fragment was oligomeric when derived from chemically crosslinked gp41. The region Ala-566-Gln-596, within the cyanogen bromide fragment, contains the oligomerization-sensitive epitopes as well as two lysine residues available for crosslinkage. This region is relatively conserved and has the propensity to form an amphipathic α-helix.