Two separate groups, González et al. and Miller and Hurley, described the three-dimensional structure of the catalytic region of inositol 1,4,5-trisphosphate 3-kinase (IP3-3K), which catalyzes the transfer of phosphate from ATP to the second messenger inositol 1,4,5-trisphosphate (IP3) to produce inositol 1,4,5,6-tetrakisphosphate. González et al. crystallized residues 187 to 461 of the human IP3-3K A isoform, whereas Miller and Hurley crystallized residues 185 to 459 of the rat IP3-3K A isoform. Both groups described N- and C-terminal lobes with a cleft in between where ATP binds, which resembles the structures of other protein kinases, and a unique four-helix substrate-binding domain that determines IP3-3K's substrate specificity and its inability to phosphorylate membrane-associated phosphoinositides.
B. González, M. J. Schell, A. J. Letcher, D. B. Veprintsev, R. F. Irvine, R. L. Williams, Structure of a human inositol 1,4,5-trisphosphate 3-kinase: Substrate binding reveals why it is not a phosphoinositide 3-kinase. Mol. Cell 15, 689-701 (2004). [Online Journal]
G. J. Miller, J. H. Hurley, Crystal structure of the catalytic core of inositol 1,4,5-trisphosphate 3-kinase. Mol. Cell 15, 703-711 (2004). [Online Journal]