IDENTIFICATION AND CLONING OF CENTAURIN-ALPHA - A NOVEL PHOSPHATIDYLINOSITOL 3,4,5-TRISPHOSPHATE-BINDING PROTEIN FROM RAT-BRAIN

Using an affinity resin and photoaffinity label based on phospholipid analogs of inositol 1,3,4,5-tetrakisphosphate (InsP(4)), we have isola ted, characterized, and cloned a 46-kDa protein from rat brain, which we have named centaurin-alpha. Binding specificity was determined usin g displacement of H-3](3-[4-benzoyldihydrocinnamidyl]propyl)-InsP(4) p hotoaffinity labeling. Centaurin-alpha displayed highest affinity for phosphatidylinositol 3,4,5-trisphosphate (PtdInsP(3)) (IC50 = 120 nm), whereas InsP(4), PtdInsP(2), and InsP(3) bound with 5-, 12-, and >50- fold lower affinity, respectively. Screening a rat brain cDNA library with a polymerase chain reaction product, generated using partial amin o acid sequence from tryptic peptides, yielded a full-length clone. Th e 2,450-base pair cDNA contained an open reading frame (ORF) encoding a novel protein of 419 amino acids. Northern analysis revealed a 2.5-k ilobase transcript that is highly expressed in brain. The deduced sequ ence contains a novel putative zinc finger motif, 10 ankyrin-like repe ats, and shows homology to recently identified yeast and mammalian Arf GTPase-activating proteins. Given the specificity of binding and enri chment in brain, centaurin-alpha is a candidate PtdInsP(3) receptor th at may link the activation of phosphoinositide 3-kinase to downstream responses in the brain.