The crystal structure of the complex of Zea mays alpha subunit with a fragment of human beta subunit provides the clue to the architecture of proteinkinase CK2 holoenzyme

The crystal structure of a complex between the catalytic or subunit of Zea mays CK2 and a 23-mer peptide corresponding the C-terminal sequence 181-203 of the human CK2 regulatory beta subunit has been determined at 3.16-Angst rom resolution. The complex, composed of two alpha chains and two peptides, presents a molecular twofold axis, with each peptide interacting with both alpha chains. In the derived model of the holoenzyme, the regulatory subun its are positioned on the opposite side with respect to the opening of the catalytic sites, that remain accessible to substrates and cosubstrates. The beta subunit can influence the catalytic activity both directly and by pro moting the formation of the alpha(2) dimer, in which each alpha chain inter acts with the active site of the other. Furthermore, the two active sites a re so close in space that they can simultaneously bind and phosphorylate tw o phosphoacceptor residues of the same substrate.