| Summary: | Candida albicans is the major fungal pathogen of humans and its cell surface mannoproteins play important roles in adhesion, interactions with the host and signal transduction. Most of the covalently attached mannoproteins are linked to the cell surface by glycosylphosphatidylinositol (GPI) anchors. Over 100 putative GPI-proteins have been identified in silico in the C. albicans genome, yet the majority remain uncharacterised with regards to their function and regulation. This study uses different approaches to define the role and regulation of selected GPI-protein genes. Expression analyses demonstrated transcriptional regulation of these genes in response to membrane and wall stresses including antifungal drugs. We propose that these genes encode proteins with important roles in cell wall remodelling. One protein, Pga54 was selected for further analysis. Null mutant and reintegrant strains were constructed and phenotypically analysed. The mutant phenotype was for the greatest parts inconclusive, but it showed a minor virulence defect in a mouse model of systemic infection. Using a tagged version of Pga54 the protein could be detected in the GPI fraction of the cell wall in wild type C. albicans cells and was shown to be higher expressed in cells subjected to stress. To establish whether they play a role in adhesion to host cells selected uncharacterised GPI proteins were heterologously expressed in the non-adherent yeast Saccharomyces cerevisiae. The newly generated S. cerevisiae strains did not show any differences in adhesion to human buccal epithelial cells. Further, the examination of tandem repeat variation in genes encoding GPI anchored proteins in different C. albicans strains indicates that this is could be a further means of creating diversity and heterogeneity at the cell surface. This study employs different methods to study the role and the dynamics of cell surface proteins. In future studies these approaches could be applied to all identified GPI proteins to obtain a comprehensive picture of cell surface diversity in Candida albicans.
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