Characterisation of the phosphatidylinositol synthase gene of Plasmodium species.

Phosphatidylinositol (PI) is a versatile lipid that not only serves as a structural component of cellular membranes, but also plays important roles in membrane anchorage of proteins and in signal transduction through distinct phosphorylated derivatives of the inositol head group. PI is synthesised by PI synthase from CDP-diacylglycerol and myo-inositol. The enzymatic activity in Plasmodium falciparum and P. knowlesi has previously been characterised at the biochemical level. Here we characterise the PI synthase gene of P. falciparum and P. knowlesi. The cDNA sequence identified a highly spliced gene consisting of nine exons and encoding a protein of 209 and 207 amino acids, respectively. High sequence conservation enabled the prediction of the PI synthase genes of P. berghei, P. chabaudi and P. vivax. All Plasmodium PI synthase proteins appear to be highly hydrophobic, although no consensus for the number and location of distinct transmembrane domains could be detected. The P. falciparum PI synthase (PfPIS) gene successfully complemented a Saccharomyces cerevisiae PIS1 deletion mutant, demonstrating its enzymatic function. Complementation efficiency was dramatically improved when hybrid constructs between N-terminal S. cerevisiae and C-terminal P. falciparum sequences were used. Determination of in vitro PIS activities of complemented yeast strains confirmed the enzymatic function of the Plasmodium protein.