Robust Utilization of Phospholipase-Generated Metabolites, Glycerophosphodiesters, by Candida albicans: Role of the CaGit1 Permease

摘要

Glycerophosphodiesters are the products of phospholipase-mediated deacylation of phospholipids. In Saccharomyces cerevisiae, a single gene, GIT1, encodes a permease responsible for importing glycerophosphodiesters, such as glycerophosphoinositol and glycerophosphocholine, into the cell. In contrast, the Candida albicans genome contains four open reading frames (ORFs) with a high degree of similarity to S. cerevisiae GIT1 (ScGIT1) Here, we report that C. albicans utilizes glycerophosphoinositol (GroPIns) and glycerophosphocholine (GroPCho) as sources of phosphate at both mildly acidic and physiological pHs. Insertional mutagenesis of C. albicans GIT1 (CaGIT1) (orf19.34), the ORF most similar to ScGit1, abolished the ability of cells to use GroPIns as a phosphate source at acidic pH and to transport [3H]GroPIns at acidic and physiological pHs, while reintegration of a GIT1 allele into the genome restored those functions. Several lines of evidence, including the detection of internal [3H]GroPIns, indicated that GroPIns is transported intact through CaGit1. GroPIns transport was shown to conform to Michaelis-Menten kinetics, with an apparent K_m of 28 ± 6 μM. Notably, uptake of label from [3H]GroPCho was found to be roughly 50-fold greater than uptake of label from [3H]GroPIns and roughly 500-fold greater than the equivalent activity in S. cerevisiae. Insertional mutagenesis of CaGIT1 had no effect on the utilization of GroPCho as a phosphate source or on the uptake of label from [3H]GroPCho. Growth under low-phosphate conditions was shown to increase label uptake from both [3H]GroPIns and [3H]GroPCho. Screening of a transcription factor deletion set identified CaPHO4 as required for the utilization of GroPIns, but not GroPCho, as a phosphate source.