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

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Abstract
CK2α 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 Å resolution, of recombinant maize CK2α (rmCK2α) 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.