Purification and characterization of an Ins(1,3,4,5)P4 binding protein from pig platelets: possible identification of a novel non-neuronal Ins(1,3,4,5)P4 receptor

A novel Ins(1,3,4,5)P4-binding protein has been purified to apparent homogeneity from solubilized membranes derived from pig platelets. It has a high affinity for Ins(1,3,4,5)P4 (Kd 6.3 +/- 0.4 nM), a Bmax of 2.5-6.0 nmol/mg of protein, and a high specificity for Ins(1,3,4,5)P4 [Kd values for Ins(1,3,4,5,6)P5, InsP6, GroPtdIns(3,4,5)P3, Ins(1,4,5)P3, Ins(3,4,5,6)P4 and L-Ins(1,3,4,5)P4 of 85.0 +/- 4.1 nM, 800.0 +/- 20.2 nM, 65.6 +/- 2.6 nM, > 10 microM, 793.3 +/- 55.6 nM and 81.0 +/- 5.9 nM respectively]. The protein has an apparent molecular mass of 104 kDa, suggesting that this peripheral tissue protein may be different from Ins(1,3,4,5)P4 binding proteins previously isolated from neuronal tissues.