Characterization of the human LPIN1‐encoded phosphatidate phosphatase isoforms

Abstract

The mammalian LPIN1 gene encodes the Mg2+‐dependent phosphatidate (PA) phosphatase, which catalyzes the dephosphorylation of PA to produce diacylglycerol (DAG), and its expression by alternative splicing produces the α and β isoforms. Here, we found a novel splice form (γ) of human lipin 1, which differs from the α form by containing additional 26 amino acids. In addition, we characterized the enzymological properties of human LPIN1α, β, and γ‐encoded PA phosphatases purified after heterologous expression in Escherichia coli. The LPIN1‐encoded PA phosphatase enzymes followed surface dilution kinetics with respect to PA using Triton X‐100/PA mixed micelles. These enzymes had similar Km values (4.2–4.5 mol %) for PA, but their Vmax values were in the order of α (34.9 μmol/min/mg) > β (24.9 μmol/min/mg) >> γ (3.4 μmol/min/mg). Although the lipin 1 isoforms showed a significant difference in catalytic activity, they were similar with respect to reaction conditions for optimum activity, inhibitors, and effectors. Supported by NIH grant GM‐28140.