The Saccharomyces cerevisiae lipin homolog is a Mg2+-dependent phosphatidate phosphatase enzyme

Mg2+-dependent phosphatidate (PA) phosphatase (3-sn-phosphatidate phosphohydrolase, EC3.1.3.4) catalyzes the dephosphorylation of PA to yield diacylglycerol and Pi. In this work, we identified the Saccharomyces cerevisiae PAH1 (previously known as SMP2) gene that encodes Mg2+-dependent PA phosphatase using amino acid sequence information derived from a purified preparation of the enzyme (Lin, Y.-P., and Carman, G. M. (1989) J. Biol. Chem. 264, 8641-8645). Overexpression of PAH1 in S. cerevisiae directed elevated levels of Mg2+-dependent PA phosphatase activity, whereas the pah1 Delta mutation caused reduced levels of enzyme activity. Heterologous expression of PAH1 in Escherichia coli confirmed that Pah1p is a Mg2+-dependent PA phosphatase enzyme and showed that its enzymological properties were very similar to those of the enzyme purified from S. cerevisiae. The PAH1-encoded enzyme activity was associated with both the membrane and cytosolic fractions of the cell, and the membrane-bound form of the enzyme was salt-extractable. Lipid analysis showed that mutants lacking PAH1 accumulated PA and had reduced amounts of diacyl-glycerol and its derivative triacylglycerol. The PAH1-encoded Mg2+-dependent PA phosphatase shows homology to mammalian lipin, a fat-regulating protein whose molecular function is unknown. Heterologous expression of human LPIN1 in E. coli showed that lipin 1 is also a Mg2+-dependent PA phosphatase enzyme.