Enhanced membrane permeabilization and antibacterial activity of a disulfide-dimerized magainin analogue

A cysteine substitution analogue of magainin-2 amide (magainin-F12W, N22C; denoted here as mag-N22C), and a disulfide-linked dimer prepared by air oxidation [(mag-N22C)(2)], were compared in their ability to release carboxyfluorescein (CF) from 100-nm large unilamellar vesicles (LUV) and to kill the Gram negative bacteria Stenotrophomonas maltophilia and Escherichia coli. The disulfide-dimerized peptide showed enhanced permeabilization and antimicrobial activity, when compared with the monomeric peptide, that was particularly marked at very low peptide concentrations. The enhanced CF-releasing activity of the dimer at low concentrations in vesicles results from (i) enhanced binding to negatively charged membrane surfaces and (ii) a low concentration dependence for permeabilization in the dimer compared to the monomer. The unique properties of the dimeric peptide suggest a role for structural diversity of antimicrobial peptides in frog skin, including the recent identification of a heterodimer composed of disulfide-linked amphipathic helical peptides [Batista et al. (2001) FEBS Lett. 494, 85-89]. Disulfide-dimerization of pore-forming, positively charged, amphipathic helical peptides may be a useful general approach to the generation of peptide antimicrobials having activity at very low concentrations.