Specific interaction of conformational polypeptides derived from HIV gp120 with human T lymphocyte CD4 receptor.

Specifically cross-linked peptides (peptomers) have been prepared from the repeating sequences of the C4 domains of glycoproteins 120 present in different isolates of human immunodeficiency virus (HIV). In order to investigate if the HIV C4 peptomers could function as gp120 protein, we have used a novel protein-binding assay to examine if and which components of the peptomers could interact with CD4 receptor in vitro. Here, we demonstrate that all the polymeric components of the HIV-1 C4 peptomer could bind to recombinant soluble CD4 protein. A similar result was also obtained with HIV-2 C4 peptomer except that the binding occured only in those of constituents having molecular weights higher than that of trimer. Remarkably, the CD4-binding was demonstrated to be specific to the HIV C4 peptomers as it did not occur with control peptomers such as Poly V3 MN and Poly NINA whose peptide sequences bore no homology to those of the HIV C4 peptomers. Furthermore, consistent with previous findings, no interaction of HIV-1 C4 monomeric peptide (419-436) with CD4 was detected under the same conditions. Since it is known that the HIV C4 peptomers have much higher contents of alpha-helical conformation than those of their monomeric peptides, we conclude that the secondary structure is a pivotal determinant for the successful CD4-binding by the peptomers. Our finding reveals a more defined molecular nature of the gp120-CD4 interaction and may be important for designing HIV vaccines and therapeutics which target the first step in the virus infection.