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Lipid Synthesis Story Now Complete

Phosphatidate phosphatase catalyzes the dephosphorylation of phosphatidate (PA) to yield diacylglycerol and P_i. There are two different types of PA phosphatase, Mg²⁺-dependent or Mg²⁺-independent, based on the cofactor requirement. Mg²⁺-dependent PA phosphatase is thought to be mainly involved in the de novo synthesis of triacylglycerol and phospholipids, but this has not been proven because the gene encoding the enzyme has yet to be found. This has changed, however, with the publication of this Paper of the Week by Gil-Soo Han and colleagues.

Using a reverse genetic approach, Han et al. identified PAH1 as the gene encoding an Mg²⁺-dependent PA phosphatase enzyme in Saccharomyces cerevisiae. Overexpression of the PAH1 gene in S. cerevisiae resulted in elevated levels of Mg²⁺-dependent PA phosphatase activity, and deletion of the gene resulted in the reduction of enzyme activity. Characterization of the Mg²⁺-dependent PA phosphatase activity resulting from the heterologous expression of PAH1 in Escherichia coli confirmed the gene-enzyme relationship. Additionally, cells containing a pah1 mutation accumulated PA and had reduced amounts of diacylglycerol and triacylglycerol. Interestingly, this gene turns out to be a homolog of the LPIN1 gene identified in mammalian cells as controlling adipogenesis. Because Mg²⁺-dependent PA phosphatase has been the only remaining enzyme in the pathway for glycerolipid synthesis whose molecular description is missing in reviews and textbooks, this work fills in a major gap currently present in our knowledge of lipid synthesis.

FOOTNOTES

See referenced article, J. Biol. Chem. 2006, 281, 9210-9218

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