Enhanced expression and purification of inositol 1,4,5-trisphosphate 3-kinase A through use of the pCold1-GST vector and a C-terminal hexahistidine tag in Escherichia coli

Inositol 1,4,5-trisphosphate 3-kinase A (IP₃K-A, alternative name: ITPKA) is a neuron-specific enzyme that converts 1,4,5-trisphosphate (IP₃) into inositol 1,3,4,5-tetrakisphosphate (IP₄) through its kinase domain. In addition, transient overexpression of IP ₃K-A induces morphological changes in dendritic spines of excitatory synapses in a kinase-independent manner, apparently by modulating the organization of the neuronal cytoskeleton. Although the procurement of a purified recombinant IP₃K-A protein would be indispensable for the biochemical elucidation of its physiological roles, production of recombinant IP₃K-A has proven technically challenging in conventional Escherichia coli expression systems. These difficulties stem from low enzyme solubility, as well as poor protein quality caused by the tendency of IP₃K-A to split into partial fragments. In present study, we newly introduced cold-shock expression vector (pCold1) together with a C-terminal hexahistidine tag (C-HIS) to enhance the expression levels of recombinant IP₃K-A in E. coli. Importantly, when compared with other commonly-employed bacterial expression systems, the pCold1 system improved the yield and the purity of full-length IP₃K-A due to the exclusion of truncated enzyme forms, and also enhanced the solubility of the enzyme. Furthermore, the functional integrity of purified IP₃K-A was confirmed in both kinase activity assay and microtubule binding assay. Recombinant IP₃K-A acquired via this modified protocol will be expected to facilitate the exploration of the enzyme's biochemical profile, both structurally and functionally.