Physical dissection of the structural elements responsible for regulatory properties and intersubunit interactions of protein kinase CK2 beta-subunit

The noncatalytic beta-subunit of protein kinase CK2 has been shown to display various and in some respects antagonistic effects on the catalytic alpha-subunit [Boldyreff et al. (1993) Biochemistry 32, 12672-12677; Meggio et al. (1994) Biochemistry 33, 4336-4342]. We have now examined the ability of peptides encompassing the N- and C-terminal regions of the beta-subunit (beta[1-77] and beta[155-215]) to mimic the functions of the whole-length beta-subunit. Peptide beta[155-215] possesses only the positive features of the beta-subunit in that it prevents thermal inactivation and stimulates basal activity of the alpha-subunit, while it does not inhibit but rather stimulates calmodulin phosphorylation. In sharp contrast, peptide beta[1-77] neither protects the alpha-subunit nor stimulates its basal activity, while acting as a powerful and specific inhibitor of calmodulin phosphorylation. Peptide beta[155-215], but not peptide beta[1-77], stably interacts with alpha-subunit and also displays remarkable self-associating properties. A shorter derivative of beta[155-215], beta[170-215], displaying weaker stimulatory properties fails to stably interact with the alpha-subunit and to give rise to dimeric/multimeric forms. These data show that the elements responsible for the negative regulation are concentrated in the N-terminal moiety of the beta-subunit, whereas the C-terminal region retains the beneficial properties of the beta-subunit and is capable of self-association and binding of the alpha-subunit. Residues between 155 and 170 are necessary for the latter functions.