CK2α/CK1α chimeras are sensitive to regulation by the CK2β subunit

The effect of CK2β on the activity of CK2α and other protein kinases that can bind this regulatory subunit is not fully understood. In an attempt to improve our understanding of this effect, chimeras of CK2α and CK1α have been constructed. These chimeras contain different portions of the CK2α amino terminal region that are involved in the interaction with CK2β to form CK2 tetramers. In the case of chimeras 1 and 2, the portions of CK2α replace the corresponding segments of CK1α. In the case of chimera 3, the fragment of CK2α is added to the whole CK1α molecule with the exception of the initial methionine. Chimera 3 has 8% of the activity of CK1αWT, while chimeras 1 and 2 are 3 orders of magnitude less active than CK1αWT. All three chimeras bind tightly to CK2β, but only chimeras 1 and 2 are significantly stimulated in their capacity to phosphorylate casein and canonical peptide substrates by addition of the regulatory subunit. No stimulation was observed with phosvitin or non-canonical peptides derived from β-catenin. CK2β protects chimeras 1 and 2 from thermal inactivation. Chimera 2 can phosphorylate CK2β and autophosphorylate; however, salt concentrations above 150 mM NaCl eliminate the phosphorylation of CK2β but not the autophosphorylation of chimera 2. Similarly, high salt decrease the stimulatory effect of CK2β on the phosphorylation of casein.