Differential stereoselectivity of D- and L-myo-inositol 1,2,4,5-tetrakisphosphate binding to the inositol 1,4,5-trisphosphate receptor and 3-kinase

Abstract

D- and L-myo-inositol 1,2,4,5-tetrakisphosphate (Ins(1,2,4,5)P-4) were investigated for their ability to bind to the D-myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P-3) receptor in a bovine adrenal cortical membrane fraction, to mobilize intracellular Ca2+ stores in Xenopus oocytes, and to bind to the rat brain Ins(1,4,5)P-3 3-kinase overexpressed and purified in E. coli. In competitive binding experiments with the Ins(1,4,5)P-3 receptor, D-Ins(1,2,4,5)P-4 effectively displaced [H-3]Ins(1,4,5)P-3 in a concentration-dependent manner with a potency comparable to that of D-Ins(1,4,5)P-3, while L-Ins(1,2,4,5)P-4 was similar to 50-fold less effective than D-Ins(1,4,5)P-3 and D-Ins(1,2,4,5)P-4. The DL-Ins(1,2,4,5)P-4 racemate bound to the Ins(1,4,5)P-3 receptor with an apparent intermediate efficiency. Injection of D-Ins(1,2,4,5)P-4 into oocytes evoked a chloride current dependent on intracellular Ca2+ mobilization in which the agonists ranked in a similar order of potency as in the Ins(1,4,5)P-3 receptor binding. On the other hand, D-Ins(1,2,4,5)P-4 only inhibited the binding of [H-3]Ins(1,4,5)P-3 to 3-kinase very weakly with a markedly reduced potency compared to D-Ins(1,4,5)P-3, indicating that D-Ins(1,2,4,5)P-4 is not an effective competitor in the phosphorylation of [H-3]Ins(1,4,5)P-3 by 3-kinase. The results, therefore, clearly indicate that D-Ins(1,2,4,5)P-4 is as effective as D-Ins(1,4,5)P3 in the binding to the receptor but not 3-kinase, and access of Ins(1,2,4,5)P-4 over the Ins(1,4,5)P-3 receptor calls for stringent stereospecificity with D-Ins(1,2,4,5)P-4 being the active form in DL-Ins(1,2,4,5)P-4-mediated Ca2+ mobilization. (C) 2000 Elsevier Science Ltd. All rights reserved.