The NH2-terminal alpha-helical domain 1-18 of dermaseptin is responsible for antimicrobial activity

Dermaseptin, a 34-amino acid residue cationic peptide, was recently shown to inhibit the growth of pathogenic fungi responsible for severe opportunistic infections accompanying immunodeficiency syndrome and the use of immunosuppressive agents. To improve our understanding of the mechanism by which dermaseptin exerts its potent antimicrobial action, a series of either NH2- or COOH-terminally truncated analogs was synthesized. These analogs were evaluated for their ability to inhibit the growth of various pathogenic agents in culture medium. Dermaseptin exerted a lytic action upon bacteria, protozoa, yeasts, and filamentous fungi at micromolar concentrations. No inhibition of proliferation was observed with human KB cells, and dermaseptin did not lyse guinea pig lymphocytes or rabbit erythrocytes at doses up to 200 micrograms/ml. Shortening the peptide chain of dermaseptin to dermaseptin-(3-34) slightly reduced the activity of the peptide, while further reduction of the chain length to residues 14-34, 16-34, 20-34, and 28-34 yielded peptide derivatives devoid of antimicrobial activity. On the other hand, lengthening the peptide chain starting from residues 1-4 to residues 1-8 and 1-18 led to a progressive recovery of the activity of the parent molecule. Whereas the central core of dermaseptin (residues 10-19) was virtually inactive, alteration of the COOH-terminal carboxylic group of dermaseptin-(1-18) to a carboxamide yielded a peptide exhibiting enhanced antimicrobial potency, yet displaying even less in vitro toxicity compared with dermaseptin. Overall, the data indicate that molecular elements responsible for the exceptional antimicrobial potency of dermaseptin are to be traced to the NH2-terminal alpha-helical amphipathic segment spanning residues 1-18 of the molecule. Dermaseptin-(1-18)-NH2 may therefore be considered as a useful and highly tractable tool for identifying key features responsible for membrane permeabilization and as a starting point for the design of new therapeutic agents.