Proteomics unravels extracellular vesicles as carriers of classical cytoplasmic proteins in Candida albicans

Abstract

The commensal fungus Candida albicans secretes a considerable number of proteins and, as in different fungal pathogens, extracellular vesicles (EVs) have also been observed. Our report contains the first proteomic analysis of EVs in C. albicans and a comparative proteomic study of the soluble secreted proteins. With this purpose, cell-free culture supernatants from C. albicans were separated into EVs and EV-free supernatant and analyzed by LC-MS/MS. A total of 96 proteins were identified including 75 and 61 proteins in EVs and EV-free supernatant, respectively. Out of these, 40 proteins were found in secretome by proteomic analysis for the first time. The soluble proteins were enriched in cell wall and secreted pathogenesis related proteins. Interestingly, more than 90% of these EV-free supernatant proteins were classical secretory proteins with predicted N-terminal signal peptide, whereas all the leaderless proteins involved in metabolism, including some moonlighting proteins, or in the exocytosis and endocytosis process were exclusively cargo of the EVs. We propose a model of the different mechanisms used by C. albicans secreted proteins to reach the extracellular medium. Furthermore, we tested the potential of the Bgl2 protein, identified in vesicles and EV-free supernatant, to protect against a systemic candidiasis in a murine model.

Keywords: Candida albicans; LC−MS/MS analysis; extracellular vesicles; moonlighting proteins; secreted proteins.