The influence of acylation on the lipid structure modulating properties of the transmembrane polypeptide gramicidin

In order to get insight into the effect of acylation of a transmembrane polypeptide on the interaction of the polypeptide with the membrane lipids we used 31P-NMR to investigate the influence of acylated gramicidins on the polymorphic phase behavior of hydrated dispersions of 1-palmitoyllysophosphatidylcholine (lyso-PC), 1,2-dioleoylphosphatidylcholine (DOPC) and 1,2-dielaidoylphosphatidylethanolamine (DEPE). Palmitoylgramicidin induces a micelle to extended bilayer organization in lyso-PC with a slightly lower efficiency than the parent gramicidin molecule. In DOPC and DEPE acylgramicidins induce the formation of HII phase at the expense of a bilayer organization with a similar high efficiency as gramicidin. The ability of acylgramicidin to induce lipid mixing between vesicles prepared of DOPC was decreased relative to gramicidin. The results are discussed in the light of the proposed models for gramicidin-induced HII phase formation and emphasize that gramicidin itself has a very strong lipid structure modulating activity.