POSITIONING OF POSITIVELY CHARGED RESIDUES IN THE V3 LOOP CORRELATES WITH HIV TYPE-1 SYNCYTIUM-INDUCING PHENOTYPE

Although the V3 loop of the envelope glycoprotein (gp120) plays a role in determining the phenotype, pathogenesis, and tropism of human immu nodeficiency virus-1 (HIV-1), there has not been any consistent correl ation between structure and phenotype, Theoretically determined struct ures of the V3 loop of gp120, from 20 different viral strains, 10 sync ytium-inducing (SI) and 10 non-syncytium-inducing (NSI) phenotype, rev ealed that all V3 loops from SI phenotypic strains had at least two po sitively charged residues in close proximity, on the same face of the loop, All of the SI phenotypic V3 loop structures were capable of form ing strong divalent electrostatic interactions with disulfated sugars. The ability to form this interaction may be a determinant of the phen otype, tropism, and pathogenicity of HIV-1 viral strains, This structu ral motif was absent in all V3 loops from viral strains with the NSI p henotype.