Identification of potential cell-surface proteins in Candida albicans and investigation of the role of a putative cell-surface glycosidase in adhesion and virulence.

Cell-surface proteins are attractive targets for the development of novel antifungals as they are more accessible to drugs than are intracellular targets. By using a computational biology approach, we identified 180 potential cell-surface proteins in Candida albicans, including the known cell-surface adhesin Als1 and other cell-surface antigens, such as Pra1 and Csa1. Six proteins (named Csf1-6 for cell-surface factors) were selected for further biological characterization. First, we verified that the selected CSF genes are expressed in the yeast and/or hyphal form and then we investigated the effect of the loss of each CSF gene on cell-wall integrity, filamentation, adhesion to mammalian cells and virulence. As a result, we identified Csf4, a putative glycosidase with an apparent orthologue in Saccharomyces cerevisiae (Utr2), as an important factor for cell-wall integrity and maintenance. Interestingly, deletion of CSF4 also resulted in a defect in filamentation, a reduction in adherence to mammalian cells in an in vitro adhesion assay, and a prolongation of survival in an immunocompetent mouse model of disseminated candidiasis. A delay in colonization of key organs (e.g. kidney) was also observed, which is consistent with a reduction in virulence of the csf4-deletion strain. These data indicate a key role for extracellular glycosidases in fungal pathogenesis and represent a new site for therapeutic intervention to cure and prevent fungal disease.