RESISTANCE TO V3-DIRECTED NEUTRALIZATION CAUSED BY AN N-LINKED OLIGOSACCHARIDE DEPENDS ON THE QUATERNARY STRUCTURE OF THE HIV-1 ENVELOPE OLIGOMER

A conserved N-glycan present within the V3 loop of gp120 modulates the sensitivity to neutralization by antibodies directed to the Vs loop. A glycan-deficient mutant of HIVLAI, designated HIVA308, displayed a 1 00-fold increase in sensitivity to neutralization by anti-V3 MAb NEA-9 205 compared to wild-type HIVLAI. This difference in sensitivity was n ot caused by an alteration of the antibody binding site itself, as NEA -9205 had equal affinity for both wild-type and mutant monomeric gp120 , In contrast, virion-associated wild-type gp120 was immunoprecipitate d less efficiently with NEA-9205 than virion-associated mutant gp120. This difference was completely abrogated, if immunoprecipitation were carried out in the presence of detergent. Furthermore, treatment of vi rion preparations with detergent exposed the C-terminal D7324 epitope, which is inaccessible on virion-associated gp120 but readily accessib le on monomeric, soluble gp120. Finally, both wild-type and mutant mon omeric, soluble gp120 were precipitated equally efficiently by NEA-920 5 in the absence of detergent. Thus, the NEA-9205 epitope was readily accessible on monomeric gp120 regardless of the presence of the N-306- glycan, and inaccessibility of the NEA-9205 epitope imparted by the N- 306-glycan was observed only on the intact envelope oligomer. (C) 1996 Academic Press, Inc.