Design and synthesis of amphipathic 3(10)-helical peptides and their interactions with phospholipid bilayers and ion channel formation.

Abstract

It has been reported that a peptide corresponding to the S4 segment in sodium channel protein is able to form voltage-dependent cation-selective 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 (ARL8), H-(Val-Arg-Leu)8-OH (VRL8), and H-(Leu-Arg-Leu)8-OH (LRL8) which were designed on the basis of the S4 segment and expected to form 3(10)-helix, were synthesized and examined with regard to conformational change by the interaction with membranes, membrane perturbation ability, ion channel formation, and antimicrobial activity. According to CD spectra, these peptides were found to form a 3(10)-helical structure in the presence of dipalmitoyl-DL-alpha-phosphatidylcholine/dipalmitoyl-DL-alpha- phosphatidylglycerol (3:1) liposomes. The experiment of the peptide-induced leakage of carboxyfluorescein from liposomes showed that all the peptides had a strong ability to perturb membranes. The peptides were able to form cation-selective ion channels in planar asolectin lipid bilayers. The conductances of the ion channels were small (approximately 2 picosiemens for VRL8 and LRL8 and approximately 23 picosiemens for ARL8), suggesting that the peptides produce narrow pores or wider pores with certain permeable barriers that are a portion of the whole channels. The differences in their conductances depend possibly on the sizes of the side chains of Ala, Val, and Leu residues. However, non of the peptides showed antimicrobial activity (minimum inhibitory concentrations, > 50 micrograms/ml). Here, we present the first evidence that the peptides can form 3(10)-helical structures with long chain lengths in a lipid bilayer environment.