Expression and characterization of a recombinant maize CK-2 α subunit

CKIIB, one of the CK-2 like enzymes which have been isolated from maize, has been shown to be a monomeric enzyme that cross-reacts with anti CK-2 α specific antibodies suggesting a possible relationship between the two proteins (Dobrowolska et al. (1992) Eur. J. Biochem. 204, 299–303). In order to support the immunological data also by biochemical and biophysical experiments the availability of a recombinant CK-2 α from maize was a prerequisite. A maize cDNA clone of maize CK-2 α was expressed in the bacterial strain BL21 (DE3). The recombinant protein was purified to homogeneity; its molecular mass on one-dimensional SDS PAGE was estimated to be 36.5 kDa. The calculated molecular mass according to the amino acid composition is 39228 Da (332 amino acids). The recombinant maize CK-2 α (rmCK-2 α) exhibited mostly the same properties as the recombinant human CK-2 α (rhCK-2 α). In several respects it behaved differently from CKIIB, thus supporting the notion that either CKIIB is encoded by another gene or it undergoes extensive posttranscriptional and/or posttranslational alterations. Three observations in particular disprove any close relatedness between CKIIB and rmCK-2 α, namely: (a) the phosphorylation of calmodulin by CKIIB is dramatically stimulated by polylysine, whereas polylysine inhibits rather than stimulating the phosphorylation of calmodulin by rmCK-2 α (and by rhCK-2 α). (b) Addition of rhCK-2 β has no significant influence on the stimulation of the calmodulin phosphorylation by CKIIB whereas in the case of rmCK-2 α and rhCK-2 α addition of rhCK-2 β is required for optimal stimulation by polylysine. (c) CKIIB does not self-assemble with rhCK-2 β to form a high molecular mass complex as it is demonstrated for rmCK-2 α.