Purification and characterization of recombinant protein kinase CK2 from Zea mays expressed in Escherichia coli

Abstract

Recombinant protein kinase subunits rmCK2α-1 and rmCK2β-1 from Zea mays were expressed separately in Escherichia coli and assembled to a fully active tetrameric holoenzyme complex in vitro. The obtained maize holoenzyme was purified to homogeneity, biochemically characterized, and compared to CK2 from human. Kinetic measurements of the recombinant maize holoenzyme (rmCK2) revealed kcat values for ATP and GTP of 4 and 2 s−1, respectively; whereas the recombinant maize catalytic subunit showed almost equal values for ATP and GTP, i.e., ca. 0.8 s−1. A comparison of the kcat/Km ratio between the maize holoenzyme and the catalytic subunit from CK2 maize shows that the incorporation of the catalytic subunit into the holoenzyme leads to a 14-fold activation in the case of ATP and 8-fold activation in the case of GTP. The maize holoenzyme is about 10 times more sensitive towards CK2 inhibitor heparin, on the other hand, it is stimulated only 0% by polylysine as compared to the human counterpart. The maize holoenzyme activity is more sensitive towards NaCl concentrations higher than those of rhCK2 and treatment with urea showed that rmCK2 holoenzyme was denatured more readily than the human holoenzyme.