Design and characterization of anchoring amphiphilic peptides and their interactions with lipid vesicles

In an effort to develop a polymer/peptide assembly for the immobilization o f lipid vesicles, we have made and characterized four water-soluble amphiph ilic peptides designed to associate spontaneously and strongly with lipid v esicles without causing significant leakage from anchored vesicles. These p eptides have a primary amphiphilic structure with the following sequences: AAAAAAAAAAAAWKKKKKK, AALLLAAAAAAAAAAAAAAAAAAAWKKKKKK, and KKAALLLAAAAAAAAAA AAAAAAAAAWKKKKKK and its reversed homologue KKKKKKWAAAAA AAAAAAAAAAAAAALLLA AKK. Two of the four the four peptides have their hydrophobic segments capp ed at both termini with basic residues to stabilize the transmembrane orien tation and to increase the affinity for negatively charged vesicles. We hav e studied the secondary structure and the membrane affinity of the peptides as well as the effect of the different peptides on the membrane permeabili ty. The influence of the hydrophobic length and the role of lysine residues were clearly established. First, a hydrophobic segment of 24 amino acids, corresponding approximately to the thickness of a lipid bilayer, improves c onsiderably the affinity to zwitterionic lipids compared to the shorter one of 12 amino acids. The shorter peptide has a low membrane affinity since i t may not be long enough to adopt a stable conformation. Second, the presen ce of lysine residues is essential since the binding is dominated by electr ostatic interactions, as illustrated by the enhanced binding with anionic l ipids. The charges at both ends, however, prevent the peptide from insertin g spontaneously in the bilayer since it would involve the translocation of a charged end through the apolar core of the bilayer. The direction of the amino acid sequence of the peptide has no significant influence on its beha vior. None of these peptides perturbs membrane permeability even at an incu bation lipid to peptide molar ratio of 0.5. Among the four peptides, AALLLA AAAAAAAAAAAAAAAAAAWKKKKKK is identified as the most suitable anchor for the immobilization of lipid vesicles. (C) 1999 John Wiley & Sons, Inc.