Fungicidal effect of antimicrobial peptide arenicin-1.

Arenicin-1 is a 21-residue peptide which was derived from Arenicola marina. In this study, we investigated the antifungal effects and its mechanism of action towards human pathogenic fungi. Arenicin-1 exerted remarkable fungicidal activity with both energy-dependent and salt-insensitive manners. To investigate the fungicidal mechanisms of arenicin-1, the membrane interactions of arenicin-1 were examined. Flow cytometric analysis, using propidium iodide (PI) and bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC(4)(3)], as well as fluorescence analysis, regarding the membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH), were conducted against Candida albicans. The results demonstrated that arenicin-1 was associated with lipid bilayers and induced membrane permeabilization. Additionally, the membrane studies in regard to liposomes resembling the phospholipid bilayer of C. albicans confirmed the membrane-disruptive potency of arenicin-1. Therefore, the present study suggests that arenicin-1 exerts its fungicidal effect by disrupting fungal phospholipid membranes.

Cell selectivity-membrane phospholipids relationship of the antimicrobial effects shown by pleurocidin enantiomeric peptides.

Previously, we investigated the antimicrobial properties of pleurocidin (Ple) enantiomers. Our studies showed that the L-enantiomer exhibited about a 2-16 fold more potent activity against bacterial strains as compared to that of the D-enantiomer. However, fungal strains were about two-fold more susceptible to the D-enantiomer than to the L-enantiomer. In this study, confocal laser scanning microscopy indicates that the Ple enantiomers internalize into the cell surface. The present results also suggest that they could be characterized by a membrane-active mechanism. To further elucidate their selective membranolytic activities, we conducted a fluorescence analysis. A study with 1,6-diphenyl-1,3,5-hexatriene, a hydrophobic molecule, showed that the L-and the D-enantiomer exert more potent antibacterial or antifungal activity than their opposite enantiomer, respectively. Furthermore, we synthesized liposomes by using representative phospholipids consisting of bacterial or fungal membranes. Our results show that the L-enantiomer causes significant dye leakage from negatively charged liposomes (PG/CL; 58:42, PC/PG; 1:1, w/w) which mimic bacterial membranes such as Staphylococcus aureus. Conversely, the D-enantiomer has more potent leakage effects against fungal liposomes (PC/PE/PI/ergosterol; 5:4:1:2, w/w/w/w, PC/ergosterol; 10:1, w/w). In summary, these results suggest that the selective antimicrobial effects of the Ple enantiomers against bacterial and fungal cells may be due to the different lipid compositions of prokaryotes and eukaryotes.