Crystal structure of the catalytic subunit of protein kinase CK2 from Zea mays at 2.1 Å resolution

CK2 alpha is the catalytic subunit of protein kinase CK2, an acidophilic and constitutively active eukaryotic Ser/Thr kinase involved in cell proliferation, A crystal structure, at 2.1 Angstrom resolution, of recombinant maize CK2 alpha (rmCK2 alpha) in the presence of ATP and Mg2+, shows the enzyme in an active conformation stabilized by interactions of the N-terminal region with the activation segment and with a cluster of basic residues known as the substrate recognition site, The close interaction between the N-terminal region and the activation segment is unique among known protein kinase structures and probably contributes to the constitutively active nature of CK2, The active centre is occupied by a partially disordered ATP molecule with the adenine base attached to a novel binding site of low specificity. This finding explains the observation that CK2, unlike other protein kinases, can use both ATP and GTP as phosphorylating agents.