Nectriatides with No Antifungal Activity Bind to Ergosterol and Potentiate the Antifungal Activity of Amphotericin B against Candida albicans.

Fungal cyclotetrapeptide nectriatide and its synthetic linear derivatives (nectriatide-based compounds, NCTs), having no antifungal activity, potentiated the antifungal activity of amphotericin B (AmB) against Candida albicans. The mechanism of action was investigated using fluorescein-conjugated and biotin-tagged probes. Microscopy revealed fluorescent probe localization at the C. albicans cell surface. The biotinyl probe binding assay toward membrane lipids showed the highest affinity for ergosterol but no affinity for cholesterol. Ergosterol binding was confirmed by a liposome disruption assay. LC-MS quantification of AmB in C. albicans revealed that NCTs increased the level of binding of AmB to C. albicans. These results indicate that NCTs bind to ergosterol on the fungal plasma membrane, subsequently localizing AmB, explaining the observed potentiation of AmB fungicidal activity.