HPLC demonstration that an all Trp-->Phe replacement in gramicidin A results in a conformational rearrangement from beta-helical monomer to double-stranded dimer in model membranes.

We have taken advantage of our previously reported high performance liquid chromatographic (HPLC) strategy to investigate the conformational behavior of the optically reversed gramicidin M (gM-), an analog of gramicidin A with all tryptophans replaced by phenylalanines, in different model membranes. It is quantitatively demonstrated for the first time that once inserted in the lipid environment, gM- (unlike the native peptide) undergoes a conformational transition from beta-helical monomers to thermodynamically stable double-stranded dimers. This transition is faster the higher the incubation temperature and can be neatly observed in both small unilamellar phospholipid vesicles and lysophospholipid micelles. The results of this study are discussed in the light of presently available data from other techniques, in the framework of the current efforts to understand structure-function relationships of linear gramicidins.