Role of the β subunit of casein kinase‐2 on the stability and specificity of the recombinant reconstituted holoenzyme

Abstract

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