Molecular mechanisms of the human pathogen <i>Candida glabrata</i> involved in the interaction with the host

Abstract

Besides superficial skin and vaginal infections Candida glabrata causes life threatening disseminated candidiasis. C. glabrata is now the second most common cause of systemic Candidiasis in humans and isolated strains show a high rate of Fluconazole resistance, which aggravates successful treatment. C. glabrata occupies a variety of niches in its human host (skin, vaginal mucosa, blood) and must therefore respond and adapt effectively to different environmental conditions. The cell wall is of utmost importance as it is the front line in respect to host pathogen interaction as well as the recognition of environmental clues. Despite the immense medical importance of C. glabrata, data on molecular mechanisms of pathogenicity are still rare. In the present study we have investigated the function of one of the most abundant GPI-anchored cell wall proteins of C. glabrata (Cwp1.1p) and its protein family as well as the proteomic changes which occur upon exposition to different environmental pH values. We found Cwp1.1p to be a major structural component of the C. glabrata cell wall, which mediates protection of the fungus from cell wall degrading enzymes such as β-1,3-glucanase. Deletion of all three CWP1 genes resulted in reduced growth at alkaline pH and remarkable structural changes in the cell wall, as indicated by enhanced sensitivity towards calcofluor white. These changes also reduced the fungus ability to adhere to epithelial cells. The exposure of C. glabrata to changing ambient pH induced copious alterations in protein expression. We found enzymes of glucose catabolism and the TCA cycle to be expressed at much higher levels at acidic than at alkaline pH, indicating that higher metabolic activity might be needed for intracellular pH homeostasis in acidic environments. At alkaline conditions protein catabolism was induced while protein synthesis was significantly downregulated, thereby shifting protein metabolism to the usage of reserves. Thus, C. glabrata seems to perceive acidic pH as less stressful. This suggestion was further supported by the observed induction of stress response proteins at alkaline pH and contrasts with the human pathogen C. albicans. In this study we performed the first systematic proteomic analysis of the global pH response of C. glabrata and characterized the important function of structural cell wall proteins, namely Cwp1p, in the cell wall of this pathogenic yeast.