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Inactivation of CaMIT1 inhibits Candida albicans phospholipomannan beta-mannosylation, reduces virulence, and alters cell wall protein beta-mannosylation
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Edité par CCSD ; American Society for Biochemistry and Molecular Biology -
International audience. Studies on Candida albicans phospholipomannan have suggested a novel biosynthetic pathway for yeast glycosphingolipids. This pathway is thought to diverge from the usual pathway at the mannose-inositol-phospho-ceramide (MIPC) step. To confirm this hypothesis, a C. albicans gene homologue for the Saccharomyces cerevisiae SUR1 gene was identified and named MIT1 as it coded for GDP-mannose:inositol-phospho-ceramide mannose transferase. Two copies of this gene were disrupted. Western blots of cell extracts revealed that strain mit1{Delta} contained no PLM. Thin layer chromatography and mass spectrometry confirmed that mit1{Delta} did not synthesize MIPC, demonstrating a role of MIT1 in the mannosylation of C. albicans IPCs. As MIT1 disruption prevented downstream {beta}-1,2 mannosylation, mit1{Delta} represents a new C. albicans mutant affected in the expression of these specific virulence attributes, which act as adhesins/immunomodulators. mit1{Delta} was less virulent during both the acute and chronic phases of systemic infection in mice (75 and 50% reduction in mortality, respectively). In vitro, mit1{Delta} was not able to escape macrophage lysis through down-regulation of the ERK1/2 phosphorylation pathway previously shown to be triggered by PLM. Phenotypic analysis also revealed pleiotropic effects of MIT1 disruption. The most striking observation was a reduced {beta}-mannosylation of phosphopeptidomannan. Increased {beta}-mannosylation of mannoproteins was observed under growth conditions that prevented the association of {beta}-oligomannosides with phosphopeptidomannan, but not with PLM. This suggests that C. albicans has strong regulatory mechanisms associating {beta}-oligomannoses with different cell wall carrier molecules. These mechanisms and the impact of the different presentations of {beta}-oligomannoses on the host response need to be defined.
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