CK2alpha/CK1alpha chimeras are sensitive to regulation by the CK2beta subunit

The effect of CK2beta on the activity of CK2alpha 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 CK2alpha and CK1alpha have been constructed. These chimeras contain different portions of the CK2alpha amino terminal region that are involved in the interaction with CK2beta to form CK2 tetramers. In the case of chimeras 1 and 2, the portions of CK2alpha replace the corresponding segments of CK1alpha. In the case of chimera 3, the fragment of CK2alpha is added to the whole CK1alpha molecule with the exception of the initial methionine. Chimera 3 has 8% of the activity of CK1alphaWT, while chimeras 1 and 2 are 3 orders of magnitude less active than CK1alphaWT. All three chimeras bind tightly to CK2beta, 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. CK2beta protects chimeras 1 and 2 from thermal inactivation. Chimera 2 can phosphorylate CK2beta and autophosphorylate; however, salt concentrations above 150 mM NaCl eliminate the phosphorylation of CK2beta but not the autophosphorylation of chimera 2. Similarly, high salt decrease the stimulatory effect of CK2beta on the phosphorylation of casein.