The design of a specific ligand of HIV gp 120

The crystal structure of CD4 suggested that the C/G(38) and C/L-44 replacements with the consequent cystine bridge formation are compatible with the native structure of that molecular moiety. As the NQGSF sequence, corresponding to the 39-43 fragment of human CD4 protein, was found to be involved in the HIV gp120 interaction, it has been synthesized in a cyclic form by adding two cysteine residues at the amino and carboxy termini. H-1-NMR studies show that the predominant solution conformation of cyclo-[CNQGSFC] is a type II beta-turn centred on the NQGS segment. Structural and dynamic properties of the peptide are also analysed in relation to the in vitro activity.