The cell wall architecture of Candida albicans wild-type cells and cell wall-defective mutants

In Candida albicans wild-type cells, the beta 1,6-glucanase-extractable gly cosylphosphatidylinositol (GPI)dependent cell wall proteins (CWPs) account for about 88% of all covalently linked CWPs. Approximately 90% of these GPI -CWPs, including Als1p and Als3p, are attached via beta 1,6-glucan to beta 1,3-glucan. The remaining GPI-CWPs are linked through beta 1,6-glucan to ch itin. The beta 1,6-glucanase-resistant protein fraction is small and consis ts of Pir-related CWPs, which are attached to beta 1,3-glucan through an al kalilabile linkage. Immunogold labelling and Western analysis, using an ant iserum directed against Saccharomyces cerevisiae Pir2p/Hsp150, point to the localization of at least two differentially expressed Pir2 homologues in t he cell wall of C. albicans. In mnn9 Delta and pmt1 Delta mutant strains, w hich are defective in N- and O-glycosylation of proteins respectively, we o bserved enhanced chitin levels together with an increased coupling of GPI-C WPs through beta 1,6-glucan to chitin. In these cells, the level of Pir-CWP s was slightly upregulated. A slightly increased incorporation of Pir prote ins was also observed in a beta 1,6-glucan-deficient hemizygous kre6 Delta mutant. Taken together, these observations show that C. albicans follows th e same basic rules as S. cerevisiae in constructing a cell wall and indicat e that a cell wall salvage mechanism is activated when Candida cells are co nfronted with cell wall weakening.