PROBABILITY OF ALAMETHICIN CONDUCTANCE STATES VARIES WITH NONLAMELLARTENDENCY OF BILAYER PHOSPHOLIPIDS

With few exceptions, membrane lipids are usually regarded as a kind of filler or passive solvent for membrane proteins. Yet, cells exquisite ly control membrane composition. Many phospholipids found in plasma me mbrane bilayers favor packing into inverted hexagonal bulk phases. It was suggested that the strain of forcing such lipids into a bilayer ma y affect membrane protein function, such as the operation of transmemb rane channels. To investigate this, we have inserted the peptide alame thicin into bilayer membranes composed of lipids of empirically determ ined inverted hexagonal phase ''spontaneous radii'' Ro, which will hav e expectably different degrees of strain when forced into bilayer form . We observe a correlation between measured Ro and the relative probab ilities of different conductance states. States of higher conductance are more probable in dioleoylphosphatidylethanolamine, the lipid of hi ghest curvature, 1/Ro, than in dioleoylphosphatidylcholine, the lipid of lowest curvature.