Perturbation of peptide conformations induced in anisotropic environments.

Reversed-phase high performance liquid chromatography (RP HPLC) has been found to be a convenient and powerful tool for the study of the secondary structure of peptides. Here, the ability of proline to perturb the secondary structures of peptides induced at aqueous-lipid interfaces and the induced conformation of polyproline peptides were investigated by means of RP HPLC. For these studies, four different complete sets of substitution analogues of model peptides expected to have specific induced conformations were used. In the first two studies, a single lysine was "walked" through two 18-residue polyproline sequences (one N-acetylated, the other not). In the remaining two studies, a proline was "walked" through two different sequences that had been found earlier to be induced into an alpha-helical conformation during RP HPLC (an 18-residue polyalanine sequence and the amphipathic 14-residue sequence Ac-LLKLLKKLLKKLKK-NH2). Sixty-eight individual analogues were synthesized for this study and the effect of the respective substitutions on retention times was determined. The results are consistent with the concept that, upon interaction with the C-18 of the stationary phase during RP HPLC, polyproline is induced into a type II helical conformation, polyalanine into an alpha-helical conformation, and Ac-LLKLLKKLLKKLKK-NH2 into an amphipathic alpha-helical array. In an extension of this study, the antimicrobial activities of Ac-LLKLLKKLLKKLKK-NH2 and its 18 proline substitution analogues were found to be inversely correlated with their RP HPLC retention times.