Membrane Perturbation by the Lipopeptide Surfactin and Detergents as Studied by Deuterium NMR

Surfactin is a lipopeptide produced by bacillus subtilis, which has been shown to permeabilize cell and model membranes by an unspecific mechanism often referred to as detergent-like. We have compared the structural effects of surfactin on lipid membranes with those of two nonionic detergents, C12EO6 and C12EO8, by means of solid-state NMR of selectively deuterated lipids. The detergents exhibit the expected behavior of increasing the lateral pressure in the headgroup region and disordering the acyl chains. In contrast, the strong activity of surfactin to destabilize membranes is not reflected in an extreme disordering of the fatty acyl chains. However, surfactin tilts the acyl chains of the lipid and leads to a reorientation of the lipid headgroup toward the membrane interior. These effects provide evidence for a rather deep insertion of the peptide moiety into the hydrophobic−hydrophilic interface of the membrane. The results are discussed in terms of the molecular parameters governing the activity of a molecule to destabilize lipid membranes and the activity of antibiotic peptides to induce unspecific leakage of membranes.