Crystallization and preliminary X-ray diffraction analysis of inositol 1,3,4,5,6-pentakisphosphate kinase from Arabidopsis thaliana

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.