Candidacidal mechanism of a Leu/Lys‐rich α‐helical amphipathic model antimicrobial peptide and its diastereomer composed of D , L ‐amino acids

We investigated the mechanism of candidacidal action of a Lys/Leu‐rich α‐helical model antimicrobial peptide (K 9 L 8 W) and its diastereomeric peptide (D 9 ‐K 9 L 8 W) composed of D , L ‐amino acids. K 9 L 8 W killed completely Candida albicans within 30 min, but D 9 ‐K 9 L 8 W killed only 72% of C. albicans even after 100 min. Tryptophan fluorescence spectroscopy indicated that the fungal cell selectivity of D 9 ‐K 9 L 8 W is closely correlated with a selective interaction with the negatively charged PC/PE/PI/ergosterol (5:2.5:2.5:1, w/w/w/w) phospholipids, which mimic the outer leaflet of the plasma membrane of C. albicans . K 9 L 8 W was able to induce almost 100% calcein leakage from PC/PE/PI/ergosterol (5:2.5:2.5:1, w/w/w/w) liposomes at a peptide:lipid molar ratio of 1:16, whereas D 9 ‐K 9 L 8 W caused only 25% dye leakage even at a peptide:lipid molar ratio of 1:2. Confocal laser‐scanning microscopy revealed that FITC‐labeled D 9 ‐K 9 L 8 W penetrated the cell wall and cell membrane and accumulated inside the cells, whereas FITC‐labeled K 9 L 8 W did not penetrate but associated with the membranes. Collectively, our results demonstrated that the candidacidal activity of K 9 L 8 W and D 9 ‐K 9 L 8 W may be due to the transmembrane pore/channel formation or perturbation of the fungal cytoplasmic membranes and the inhibition of intracellular functions, respectively. Finally, D 9 ‐K 9 L 8 W with potent anti‐ Candida activity but no hemolytic activity may be potentially a useful lead compound for the development of novel antifungal agents. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.