ROLE OF THE BETA SUBUNIT OF CASEIN KINASE-2 ON THE STABILITY AND SPECIFICITY OF THE RECOMBINANT RECONSTITUTED HOLOENZYME

Recombinant human alpha-subunit from casein kinase-2 (CK-2) was subjected, either alone or in combination with recombinant human beta-subunit, to high temperature, tryptic digestion and urea treatment. In all three cases, it was shown that the presence of the beta-subunit could drastically reduce the loss of kinase activity, strongly suggesting a protective function for the beta-subunit. Assaying different peptides for specificity toward the recombinant alpha-subunit and the recombinant reconstituted enzyme, showed that the presence of the beta-subunit could modify the specificity of the catalytic alpha-subunit. Therefore, a dual function for the beta-subunit is proposed which confers both specificity and stability to the catalytic alpha-subunit within the CK-2 holoenzyme complex. The peptide DLEPDEELEDNPNQSDL, reproducing the highly acidic amino acid 55-71 segment of the human beta-subunit, counteracts the stimulatory effect of the beta-subunit on the alpha-subunit activity and partially substitutes the beta-subunit in conferring thermal stability to the alpha-subunit. No such effect is induced by the peptide MSSSEEVSW, reproducing the N-terminal segment of the beta-subunit including the autophosphorylation site. It is suggested that the acidic domain of the beta-subunit, encompassing residues 55-71, plays a role in the interactions between the beta and alpha-subunits.