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 a-helical model antimicrobial peptide (K9L8W) and its diastereomeric peptide (D-9-K9L8W) composed of D,L-amino acids. K9L8W killed completely Candida albicans within 30 min, but D-9-K9L8W killed only 72% of C. albicans even after 100 min. Tryptophan fluorescence spectroscopy indicated that the fungal cell selectivity of D-9-K9L8W 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. K9L8W 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-K9L8W 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-K9L8W penetrated the cell wall and cell membrane and accumulated inside the cells, whereas FITC-labeled K9L8W did not penetrate but associated with the membranes. Collectively, our results demonstrated that the candidacidal activity of K9L8 W and D-9-K9L8W 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-K9L8W with potent anti-Candida activity but no hemolytic activity may be potentially a useful lead compound for the development of novel antifungal agents. Copyright (c) 2010 European Peptide Society and John Wiley & Sons, Ltd.