Mechanism of anti-HIV activity of succinylated human serum albumin

In the present study, we described the interaction of succinylated human se rum albumin (Suc-HSA), a negatively charged anti-HIV-1 active protein, with HIV-1 gp120 and in detail with the third variable domain of gp120 (V3 loop ). To this end, different assay formats were tested in which gp120- and V3- related peptides were presented in various configurations in order to inves tigate the effect of the conformational structure of the V3 loop on the int eraction with negatively charged albumins. When gp120 presented via a lecti n was used, it was observed that Suc-HSA bound to native gp120. The binding site appeared to be located at or near the thrombin digestion site (GPGRAF sequence) in the V3 loop of gp120, since the cleavage of the loop resulted in decreased binding of Suc-HSA. In addition, Suc-HSA was able to protect the V3 region of gp120 from cleaving with thrombin. In contrast, significan t binding of Suc-HSA to V3 loop or gp120 peptides was not observed when bot h were presented in a fluid phase system, suggesting the involvement of a m onovalent low affinity binding of Suc-HSA. Using overlapping peptides delin eating the whole V3 loop immobilized to CNBr-Sepharose, we noticed that the interaction of the V3 loop with Suc-HSA was predominantly induced by elect rostatic interactions between positively charged linearized peptide fragmen ts and Suc-HSA and was positively influenced by the presence of hydrophobic amino in the V3 loop fragments as well. Moreover, the highest affinity sit e was located at sites near the GPGRAF sequence These observations add to t he evidence, collected earlier, that Suc-HSA interferes at the level of vir us entry, independent of interaction with the CD4 receptor. Since the recen tly discovered chemokine receptors are negatively charged, we can hypothesi ze that Suc-HSA is able to prevent the positively charged V3 loop from inte racting with these types of receptors, thereby inhibiting virus entry. BIOC HEM PHARMACOL 57;8:889-898, 1999. (C) 1999 Elsevier Science Inc.