Identification of salivary basic proline-rich proteins as receptors for Candida albicans adhesion

The adherence of Candida albicans cells to oral surfaces is believed to be an important step in the development of oral candidosis. Electrophoretically separated parotid salivary proteins were transferred to nitrocellulose membranes and incubated with [35S]methionine-radiolabelled C. albicans cells in a cell overlay adherence assay. A subset of four proteins with apparent molecular masses of 17, 20, 24 and 27 kDa (designated bands A-D) acted as receptors for cells of C. albicans ATCC 10261 and four clinical C. albicans isolates, in overlay assays. The N-terminal amino acid sequence of bands A-D indicated that these proteins were members of the basic proline-rich protein (bPRP) family. Digestion of protein A with endoproteinase Glu-C resulted in a single band (designated Ap) detected by Coomassie blue staining after SDS-PAGE. This band was not bound by C. albicans cells in overlay assays and comprised two fragments, designated ApN and ApC. These fragments had N-terminal sequences corresponding to the N-terminal and post endoproteinase Glu-C cleavage site sequences of bPRP IB-6 and had molecular masses of 6189 and 4261 Da as determined by mass spectrometry. Thus intact bPRP IB-6, and other bPRPs, may act as receptors for C. albicans adhesion.