SECONDARY STRUCTURE AND LOCATION OF A MAGAININ ANALOG IN SYNTHETIC PHOSPHOLIPID-BILAYERS

Magainins are cationic, membrane-active peptides which show broad-spec trum antimicrobial activity. We have investigated the secondary struct ure and location of an analogue of magainin 2 in synthetic phospholipi d bilayers using a combination of Fourier transform infrared (FTIR) sp ectroscopy and solid-state nuclear magnetic resonance (NMR) spectrosco py. Ala(19)-magainin 2 amide exhibits both alpha-helix and beta-sheet secondary structures in lipid bilayers containing either dipalmitoylph osphatidylglycerol (DPPG) or a 1:1 molar mixture of DPPG and dipalmito ylphosphatidylcholine (DPPC). The combination of FTIR and solid-state NMR results suggests that there are two populations of peptide. The se condary structure of one population is alpha-helix while that of the o ther population is beta-sheet. We demonstrate that the solid-state NMR technique, rotational-echo double resonance (REDOR), can be used to m easure both intra- and intermolecular dipole-dipole interactions in me mbrane-bound peptides. Our REDOR experiments indicate that alpha-helic al Ala(19)-magainin 2 amide is bound near the phospholipid head groups .