Pharmacophore determination of a gp120 C terminal-derived anti-HIV peptide construct interfering with membrane fusion suggesting that processing of the gp120 C terminus is a prelude to fusion

A multiple antigen peptide [CLIV; (PTKAKRR(1)VQREKR(2))(4) -K-2-K-betaA] from the C terminus of the gp120 subunit of HIV Env inhibits Env-mediated cell-to-cell fusion through direct interference with the process (Virology 2000; 273: 169). We have examined various CLIV analogs using a cell-to-cell fusion assay, receptor binding assays, and molecular modeling to further address the characteristics of the peptide responsible for its anti-HIV activity. We show that (1) CLIV does not interfere with Env binding to CD4 and does not interact with the binding site of Env on CXCR4; (2) CLIV does not inhibit protease activities already reported to play a role in fusion; and (3) the pharmacophore is composed of cleavage site(1) with amino acid residues at its C terminal end. Based on our data and on the literature, we propose that CLIV interferes with processing of the gp120 C terminus at site1 by the lymphocyte surface after CD4 binding. Our hypothesis implies that the cleavage region of Env is submitted to a stepwise processing including the known intracellular cleavage of gp160 at site(2) in order to set the activation of the fusion peptide and a yet unexplored cleavage at site1 by the target cell surface that triggers fusion.