The GPI-modified proteins Pga59 and Pga62 of Candida albicans are required for cell wall integrity

Abstract

The fungal cell wall is essential in maintaining cellular integrity and plays key roles in the interplay between fungal pathogens and their hosts. ThePGA59andPGA62genes encode two short and related glycosylphosphatidylinositol-anchored cell wall proteins and their expression has been previously shown to be strongly upregulated when the human pathogenCandida albicansgrows as biofilms. Using GFP fusion proteins, we have shown that Pga59 and Pga62 are cell-wall-located,N- andO-glycosylated proteins. The characterization ofC. albicans pga59Δ/pga59Δ,pga62Δ/pga62Δ andpga59Δ/pga59Δpga62Δ/pga62Δ mutants suggested a minor role of these two proteins in hyphal morphogenesis and that they are not critical to biofilm formation. Importantly, the sensitivity to different cell-wall-perturbing agents was altered in these mutants. In particular, simultaneous inactivation ofPGA59andPGA62resulted in high sensitivity to Calcofluor white, Congo red and nikkomicin Z and in resistance to caspofungin. Furthermore, cell wall composition and observation by transmission electron microscopy indicated an altered cell wall structure in the mutant strains. Collectively, these data suggest that the cell wall proteins Pga59 and Pga62 contribute to cell wall stability and structure.