Candida albicans phosphatidylinositol synthase has common features with both Saccharomyces cerevisiae and mammalian phosphatidylinositol synthases

Abstract

Phosphatidylinositol (PI) synthase (cytidine 5′‐diphospho (CDP)‐1,2‐diacyl‐sn‐glycerol:myo‐inositol 3phosphatidyltransferase, EC 2.7.8.11) was isolated from the microsomal cell fraction of Candida albicans. The Triton X‐100 extracted enzyme was enriched 140‐fold by affinity chromatography on CDP‐diacylglycerol–Sepharose. The enzyme had a pH optimum at 9·5 in glycine/NaOH buffer. It had an absolute requirement for Mg2+ or Mn2+ and was inhibited by Ca2+ and Zn2+. Maximal activity was at 0·2–0·6 mm‐CDP‐diacylglycerol, higher concentrations inhibited the enzyme. With 2′‐deoxy‐CDP‐diacylglycerol as the lipid substrate, optimal activity was at 0·7 mm. The Km for myo‐inositol was determined to be 0·55 mm. The optimal temperature for the PI synthase reaction was 55°C. The C. albicans PI synthase shows differences to the Saccharomyces cerevisiae enzyme, such as activation by bivalent cations, inhibition by nucleotides, temperature optimum and activation energy, but also to the human PI synthase in preference for the lipid substrates, inhibition by nucleoside monophosphates and stabilization by Mn2+ and phospholipids.

Regulated transcription of theSaccharomyces cerevisiaephosphatidylinositol biosynthetic gene,PIS1, yields pleiotropic effects on phospholipid synthesis

“…1). Phosphatidylinositol is found in many organisms and PIS1 homologs and/or the cognate enzyme activity have been identified in Toxoplasma (Seron et al , 2000), Mycobacteria (Salman et al , 1999; Jackson et al , 2000), Candida (Antonsson & Klig, 1996), Arabidopsis (Xue et al , 2000), mammals, and humans (Antonsson & Klig, 1996). The Saccharomyces cerevisiae PIS1 gene is essential for viability (Nikawa et al , 1987) and phosphatidylinositol is the third most abundant phospholipid in the membranes of S. cerevisiae , where it represents 12–27% of the total phospholipid composition (Paltauf et al , 1992).…”