Homo sapiens Dullard Protein Phosphatase Shows a Preference for the Insulin-Dependent Phosphorylation Site of Lipin1

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Abstract
Human lipin1 catalyzes the highly regulated conversion of phosphatidic acids to diacylglycerides. Lipin’s cellular location, protein partners, and biological function are directed by phosphorylation−dephosphorylation events catalyzed by the phosphoserine phosphatase dullard. To define the determinants of dullard substrate recognition and catalysis, and hence, lipin regulation, steady-state kinetic analysis was performed on phosphoserine-bearing nonapeptides based on the phosphorylation sites of lipin. The results demonstrate that dullard shows specificity for the peptide corresponding to the insulin-dependent phosphorylation site (Ser106) of lipin with a kcat/Km of 2.9 × 104 M−1 s−1. These results are consistent with a coil−loop structure for the insulin-dependent phosphorylation site on human lipin1 and make unlikely the requirement for an adaptor protein to confer activity such as that proposed for the yeast homologue.