Identification and characterization of a Sac domain-containing phosphoinositide 5-phosphatase

We have characterized a novel Sac domain-containing inositol phosphatase, hSac2. It was ubiquitously expressed but especially abundant in the brain, heart, skeletal muscle, and kidney. Unlike other Sac domain containing proteins, hSac2 protein exhibited B-phosphatase activity specific for phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate. This is the first time that the Sac domain has been reported to possess 5-phosphatase activity. Its B-phosphatase activity for phosphatidylinositol 4,5-bisphosphate (K-m = 14.3 muM) was comparable with those of Type II 5-phosphatases. These results imply that hSac2 functions as an inositol polyphosphate 5-phosphatase.