Fluid or gel phase lipid bilayers to study peptide-membrane interactions?

Since many studies on peptide-membrane interactions are carried out only with fluid phase lipid bilayers (L _α -phase, absence of cholesterol) we have investigated whether this phase is really a suitable model for biological membranes. For this purpose the action of melittin on zwitterionic and negatively charged phospholipid bilayers, in the absence and presence of 30 mol% cholesterol, was investigated by solid state ³¹P-NMR. From the NMR point of view, it appears that systems composed of a single phospholipid best mimic the sterol-containing system a few degrees below the gel-to-fluid phase transition, i. e., in the rippled phase (P _β' ). It is then proposed that a relatively rigid membrane containing local defects, rather than a L _α -bilayer, is required as an appropriate model for natural membranes when probing the action of melittin. Such requirements might be crucial when studying peptide-lipid interactions. Received: 5 February 1996 / Accepted: 1 July 1996