DESIGN AND SYNTHESIS OF AMPHIPATHIC 3(10)-HELICAL PEPTIDES AND THEIR INTERACTIONS WITH PHOSPHOLIPID-BILAYERS AND ION-CHANNEL FORMATION

It has been reported that a peptide corresponding to the S-4 segment i n sodium channel protein is able to form voltage-dependent cation-sele ctive ion channels (Tosteson, M. T., Auld, D. S., and Tosteson, D. C. (1989) Proc. Natl. Acad. Sci. U.S. A. 86, 707-710). However biological and other physical properties remain unexamined. In the present study , three peptides, H-(Ala-Arg-Leu)(8)-OH (ARL(8)), H-(Val-Arg-Leu)(8)-O H (VRL(8)), and H-(Leu-Arg-Leu)(8)-OH (LRL(8)) which were designed on the basis of the S-4 Segment and expected to form 3(10)-helix, were sy nthesized and examined with regard to conformational change by the int eraction with membranes, membrane perturbation ability, ion channel fo rmation, and antimicrobial activity. According to CD spectre, these pe ptides were found to form a 3(10)-helical structure in the presence of dipalmitoyl-DL-alpha-phosphatidylcholine/ dipalmitoyl-DL-alpha-phosph atidylglycerol (3:1) liposomes. The experiment of the peptide-induced leakage of carboxyfluorescein from Liposomes showed that all the pepti des had a strong ability to perturb membranes. The peptides were able to form cation-selective ion channels in planar asolectin lipid bilaye rs. The conductances of the ion channels were small (similar to 2 pico siemens for VRL(8) and LRL(8) and similar to 23 picosiemens for ARL(8) ), suggesting that the peptides produce narrow pores or wider pores wi th certain permeable barriers that are a portion of the whole channels . The differences in their conductances depend possibly on the sizes o f the side chains of Ala, Val, and Leu residues. However, non of the p eptides showed antimicrobial activity (minimum inhibitory concentratio ns, >50 mu g/ml). Here, we present the first evidence that the peptide s can form 3(10)-helical structures with long chain lengths in a lipid bilayer environment.