IDENTIFICATION OF RAT-BRAIN P42(IP4), A HIGH-AFFINITY INOSITOL(1,3,4,5)TETRAKISPHOSPHATE PHOSPHATIDYLINOSITOL(3,4,5)TRISPHOSPHATE BINDING-PROTEIN

Inositol(1,3,4,5)tetrakisphosphate (InsP(4)) and phosphatidylinositol( 3,4,5)trisphosphate (PtdInsP(3)) are two potential second messengers w ith a still largely unknown mode of action. We recently cloned the 42 kDa protein p42(IP4) previously purified from pig cerebellum, which bi nds InsP(4) (K-d similar to 2 nM) and PtdInsP3 with comparable affinit ies (Stricker et al., FEES Lett. 405 (1997) 229). The protein p42(IP4) (pig) is highly homologous to centaurin-alpha, a larger protein of 46 kDa, derived from a rat brain cDNA library clone (Hammonds-Odie et al ., J. Biol. Chem. 271 (1996) 18859). Here we investigated whether also p42(IP4) is expressed in rat brain and how it might be related to cen taurin-a. When we carried out RT-PCR using mRNA from brain of rats of different ages we obtained several clones corresponding to p42(IP4), b ut not to centaurin-alpha. The existence of p42(IP4) in rat brain is s upported by the following findings: (1) biochemical analysis of the pu rified rat brain protein shows inositol phosphate ligand affinities id entical to those of the protein from other species; (2) Western blot a nalysis of rat brain membrane fractions using a peptide-specific antis erum revealed only the 42 kDa protein (p42(IP4)), but did not give evi dence for the occurrence of a larger 46 kDa centaurin-alpha-like prote in in rat brain; and (3) the amino acid sequences deduced from p42(IP4 ) cDNA are highly homologous in several species and are confirmed by p rotein fragment microsequences. Thus, p42(IP4) from rat brain which ha s two pleckstrin homology domains is a protein largely conserved betwe en different species and most likely has an important function in inos itol phosphate or inositol lipid signal transduction. (C) 1998 Elsevie r Science B.V. All rights reserved.