Heparin and its derivatives bind to HIV-1 recombinant envelope glycoproteins, rather than to recombinant HIV-1 receptor, CD4

We have employed a direct radiolabel binding assay to investigate theinteraction between3H-heparin and recombinant envelope glycoproteins,rgp120s, derived from several different isolates of HIV-1. Comparabledose-dependent binding is exhibited by rgp120s from isolates IIIB, GB8, MNand SF-2. Under identical experimental conditions the binding of3H- heparinto a recombinant soluble form of the cellular receptor for gp120, CD4, isnegligible. The binding of3H-heparin to rgp120 is competed for by excessunlabeled heparin and certain other, but not all, glycosaminoglycan andchemically modified heparins. Of a range of such polysaccharides tested,ability to compete with3H-heparin for binding was strictly correlated withinhibition of HIV-1 replication in vitro. Those possessing potentanti-HIV-1 activity were effective competitors, whereas those having no orlittle anti-HIV-1 activity were poor competitors. Scatchard analysisindicates that the K d of the interaction between heparin and rgp120 is 10nM. Binding studies conducted in increasing salt concentrations confirmthat the interaction is ionic in nature. Synthetic 33-35 amino acidpeptides based on the sequence of the V3 loop of gp120 also bind to heparinwith high affinity. V3 loop peptides that are cyclized due to terminalcysteine residues show more selective binding than their uncyclizedcounterparts. Overall, these data demonstrate further that heparin exertsits anti-HIV-1 activity by binding to the envelope glycoprotein of HIV-1,rather than its cellular receptor, CD4. This study confirms that the V3loop of gp120 is the site at which heparin exerts its anti- HIV-1 activity.Moreover, it reveals that high affinity binding to heparin is shared by allfour rgp120s examined, despite amino acid substitutions within the V3 loop.