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 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 membrane. The biotinyl probe binding assay towards 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 AmB binding 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.