Interaction between amphipathic peptides and phospholipid membranes: a deuterium NMR study.

The actions of bee venom melittin and of delta-lysin from Staphylococcus aureus on membranes have been monitored by solid state deuterium NMR. Despite inducing quite similar effects on dipalmitoylphosphatidylcholine, significant differences can be shown depending on temperature and on the lipid to peptide molar ratio, Ri. In the fluid phases, for moderate amounts of toxins and at temperatures T>Tc (Tc gel to fluid transition temperature), analysis of the quadrupolar splittings in terms of chain ordering indicates that both melittin and delta-lysin similarly disorder the membrane. The addition of greater amounts of toxins (Ri=4), results in the occurrence of very small structures. At temperatures above but close to Tc, melittin preferentially orders the center of the bilayer while delta-lysin promotes ordering throughout the entire bilayer thickness. These effects are interpreted as reflecting different locations of the peptides with respect to the membrane surface. In the gel phase, for lipid to peptide molar ratios >15, melittin induces isotropic lines reflecting the presence of small discoidal structures whereas delta-lysin does not. The ability of both toxins to induce bilayer fragmentation is proposed as a possible step in the direct lysis of membranes. [ABSTRACT FROM AUTHOR]