Vesicular self-assembly of a helical peptide in water

The formation of a molecular assembly composed of a naturally occurring peptide with a helical structure was investigated. Gramicidin A, a 15-mer peptide antibiotic, was conjugated with poly(ethylene glycol) (PEG, average molecular weight 600). This peptide conjugate formed vesicles with an unilamellar membrane in water as shown by frozen-hydrated/cryo-transmission electron microscopy (cryo-TEM) observations. The peptide fragment adopted an antiparallel double-helix conformation. The vesicles of the gramicidin conjugate encapsulating PEG showed much greater stability than encapsulation by dimyristoylphosphatidylcholine liposomes with respect to resistance to collapse upon detergent addition. Since the peptide membrane core is constituted of the secondary structured units, the peptide vesicles (named peptosomes) may be advantageous to functional membranes due to their highly regular structure.