On the contribution of stereochemistry to human ITPK1 specificity: Ins(1,4,5,6)P-4 is not a physiologic substrate

Abstract

Ins(1,4,5,6)P-4, a biologically active cell constituent, was recently advocated as a substrate of human Ins(3,4,5,6)P4 1-kinase (hITPK1), because stereochemical factors were believed relatively unimportant to specificity [Miller, G.J., Wilson, M.P., Majerus, P.W. and Hurley, J.H. (2005) Specificity determinants in inositol polyphosphate synthesis: crystal structure of inositol 1,3,4-triphosphate 5/6-kinase. Mol. Cell. 18, 201-212]. Contrarily, we provide three examples of hITPK1 stereospecificity. hITPK1 phosphorylates only the 1-hydroxyl of both Ins(3,5,6)P-3 and the meso-compound, Ins(4,5,6)P-3. Moreover, h1TPKI has > 13,000-fold preference for Ins(3,4,5,6)P4 over its enantiomer, Ins(1,4,5,6)P4. The biological significance of hITPK1 being stereospecific, and not physiologically phosphorylating Ins (1,4,5,6)P4, is reinforced by our demonstrating that Ins(1,4,5,6)P4 is phosphorylated (K-m = 0.18 mu M) by inositolphosphate-multikinase. Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.