Hydrophobic cell wall protein glycosylation by the pathogenic fungus Candida albicans

Abstract

Cell surface hydrophobicity influences adhesion and virulence of the opportunistic fungal pathogen Candida albicans. Previous studies have shown that cell surface hydrophobicity is due to specific proteins that are exposed on hydrophobic cells but are masked by long fibrils on hydrophilic cells. This observation suggests that hydrophobic cell wall proteins may contain little or no mannosylation. In the present study, the glycosylation levels of three hydrophobic cell wall proteins (molecular mass range between 36 and 40 kDa) derived from yeast cells were examined. One hydrophilic protein (90 kDa) was also tested. Various endoglycosidases (endoglycosidase F – N-glycosidase F, O-glycosidase, β-mannosidase, N-glycosidase F), an exoglycosidase (α-mannosidase), and trifluoromethane sulfonic acid were used to deglycosylate the proteins. All four proteins were reactive to the lectin concanavalin A, demonstrating that they were mannoproteins. However, gel electrophoresis of the control and treated proteins revealed that mannosyl groups of hydrophobic proteins were less than 2 kDa in size, while the mannosyl group of the hydrophilic protein had a molecular mass of approximately 20 kDa. These results suggest that unlike many hydrophilic proteins, hydrophobic proteins may have low levels of glycosylation. Changes in glycosylation may determine exposure of hydrophobic protein regions at the cell surface.Key words: Candida albicans, cell wall, mannoproteins, hydrophobicity, fibrils.