The Candida albicans homologue of PIG-P, CaGpi19p: gene dosage and role in growth and filamentation

Abstract

Glycosylphosphatidyl inositol (GPI)-anchored proteins inCandida albicansare responsible for a vast range of functions, and deletions in certain GPI-anchored proteins severely reduce adhesion and virulence of this organism. In addition, completely modified GPIs are necessary for virulence. GPI anchor biosynthesis is essential for viability and starts with the transfer ofN-acetylglucosamine to phosphatidylinositol. This step is catalysed by a multi-subunit complex, GPI–N-acetylglucosaminyltransferase (GPI–GnT). In this, the first report to our knowledge on a subunit of theCandidaGPI–GnT complex, we show thatCaGpi19p is the functional equivalent of theSaccharomyces cerevisiaeGpi19p. An N-terminal truncation mutant ofCaGpi19p functionally complements a conditionally lethalS. cerevisiae gpi19mutant. Further, we constructed a conditional null mutant ofCaGPI19by disrupting one allele and placing the remaining copy under the control of the MET3 promoter. Repression leads to growth defects, cell wall biogenesis aberrations, azole sensitivity and hyperfilamention. In addition, there is a noticeable gene dosage effect, with the heterozygote also displaying intermediate degrees of most phenotypes. The mutants also displayed a reduced susceptibility to the antifungal agent amphotericin B. Collectively, the results suggest thatCaGPI19is required for normal morphology and cell wall architecture.