SPIN-LABEL ELECTRON-SPIN-RESONANCE STUDIES ON THE INTERACTIONS OF LYSINE PEPTIDES WITH PHOSPHOLIPID-MEMBRANES

The interactions of lysine oligopeptides with dimyristoyl phosphatidyl glycerol (DMPG) bilayer membranes were studied using spin-labeled lipi ds and electron spin resonance spectroscopy. Tetralysine and pentalysi ne were chosen as models for the basic amino acid clusters found in a variety of cytoplasmic membrane-associating proteins, and polylysine w as chosen as representative of highly basic peripherally bound protein s. A greater motional restriction of the lipid chains was found with i ncreasing length of the peptide, while the saturation ratio of lipids per peptide was lower for the shorter peptides. In DMPG and dimyristoy lphosphatidylserine host membranes, the perturbation of the lipid chai n mobility by polylysine was greater for negatively charged spin-label ed lipids than for zwitterionic lipids, but for the shorter lysine pep tides these differences were smaller. In mixed bilayers composed of DM PG and dimyristoylphosphatidylcholine, little difference was found in selectivity between spin-labeled phospholipid species on binding penta lysine. Surface binding of the basic lysine peptides strongly reduced the interfacial pK of spin-labeled fatty acid incorporated into the DM PG bilayers, to a greater extent for polylysine than for tetralysine o r pentalysine at saturation. The results are consistent with a predomi nantly electrostatic interaction with the shorter lysine peptides, but with a closer surface association with the longer polylysine peptide.