Crystallographic studies of casein kinase I delta toward a structural understanding of auto-inhibition

A recombinant form of mammalian casein kinase I delta (CKIdelta) containing the catalytic domain and an auto-inhibitory domain was expressed in Escherichia coli, purified and crystallized. X-ray data were collected to 2.4 A resolution, and the crystals belong to space group C2221. Molecular replacement using the structure of the catalytic domain of CKIdelta yielded strong electron density for residues in the model, but no interpretable density was found for the inhibitory domain. A conserved intermolecular contact suggests the formation of dimers which would inhibit the activity of this protein kinase.