A TARGET OF PHOSPHATIDYLINOSITOL 3,4,5-TRISPHOSPHATE WITH A ZINC-FINGER MOTIF SIMILAR TO THAT OF THE ADP-RIBOSYLATION-FACTOR GTPASE-ACTIVATING PROTEIN AND 2 PLECKSTRIN HOMOLOGY DOMAINS

We have purified a protein that binds phosphatidylinositol 3,4,5-trisp hosphate [PtdIns(3,4,5)P-3] using beads bearing a PtdIns(3,4,5)P-3 ana logue. This protein, with a molecular mass of 43 kDa, was termed PtdIn s(3,3,5)P-3-binding protein. The partial amino acid sequences were det ermined and a full-length cDNA encoding the protein was isolated from bovine brain cDNA library. The clone harbored an open reading frame of 373 amino acids which contained one zinc finger motif similar to that of ADP-ribosylation-factor GTPase-activating protein and two pleckstr in homology domains. The entire sequence was 83% similar to centaurin alpha, another PtdLns(3,3,5)P-3-binding protein. The protein bound Ptd Ins(3,4,5)P, with a higher affinity than it did inositol 1,3,4,5-tetra kisphosphate, phosphoatidylinositol 4,5-bisphosphate, phosphatidylinos itol 3,4-bisphosphate, and phosphatidylinositol 3-phosphate suggesting that the binding to PtdIns(3,3,5)P-3 was specific. The binding activi ty was weaker in the mutants with a point mutation in the conserved se quences in each pleckstrin homology domain. Introduction of both mutat ions abolished the activity. These results suggest that this new bindi ng protein binds PtdIns(3,4,5)P-3 through two pleckstrin domains prese nt in the molecule.