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

The effect of CK2 beta on the activity of CK2 alpha 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 CK2 alpha and CK1 alpha have been constructed. These chimeras contain different portions of the CK2 alpha amino terminal region that are involved in the interaction with CK2 beta to form CK2 tetramers. In the case of chimeras 1 and 2, the portions of CK2 alpha replace the corresponding segments of CK1 alpha. In the case of chimera 3, the fragment of CK2 alpha is added to the whole CK1 alpha molecule with the exception of the initial methionine. Chimera 3 has 8% of the activity of CK1 alpha(WT), while chimeras 1 and 2 are 3 orders of magnitude less active than CK1 alpha(WT). All three chimeras bind tightly to CK2 beta, 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 beta-catenin. CK2 beta protects chimeras 1 and 2 from thermal inactivation. Chimera 2 can phosphorylate CK2 beta and autophosphorylate; however, salt concentrations above 150 mM NaCl eliminate the phosphorylation of CK2 beta but not the autophosphorylation of chimera 2. Similarly, high salt decrease the stimulatory effect of CK2 beta on the phosphorylation of casein.