Inositol 1,3,4,5,6-pentakisphosphate kinase from A. thaliana has been expressed in E. coli, purified and crystallized and diffraction data have been collected to 2.3 Å resolution. Two heavy-atom crystal derivatives are under study.
Inositol 1,3,4,5,6-pentakisphosphate kinase (IP5 2-K) is an enzyme involved in inositol metabolism that synthesizes IP6 (inositol 1,2,3,4,5,6-hexakisphosphate) from inositol 1,3,4,5,6-pentakisphosphate (IP5) and ATP. IP6 is the major phosphorus reserve in plants, while in mammals it is involved in multiple cellular events such as DNA editing and chromatin remodelling. In addition, IP6 is the precursor of other highly phosphorylated inositols which also play highly relevant roles. IP5 2-K is the only enzyme that phosphorylates the 2-OH axial position of the inositide and understanding its molecular mechanism of substrate specificity is of great interest in cell biology. IP5 2-K from Arabidopsis thaliana has been expressed in Escherichia coli as two different fusion proteins and purified. Both protein preparations yielded crystals of different quality, always in the presence of IP6. The best crystals obtained for X-ray crystallographic analysis belonged to space group P212121, with unit-cell parameters a = 58.124, b = 113.591, c = 142.478 Å. Several diffraction data sets were collected for the native enzyme and two heavy-atom derivatives using a synchrotron source.