3-DIMENSIONAL STRUCTURE OF MAMMALIAN CASEIN KINASE-I - MOLECULAR-BASIS FOR PHOSPHATE RECOGNITION

The three-dimensional structure for the catalytic region of the mammal ian protein kinase, casein kinase I delta (CKI delta), has been solved by X-ray crystallography to a resolution of 2.3 Angstrom. A truncatio n mutant of CKI delta lacking the C-terminal autoinhibitory region was expressed in Escherichia coli, purified, and crystallized. The struct ure was solved by molecular replacement using the crystal structure of the catalytic domain of a CKI homolog from Schizosaccharomyces pombe, Cki1. A tungstate derivative confirmed the initial molecular replacem ent solution and identified an anion binding site which may contribute to the unique substrate specificity of CKI. Like other protein kinase s, the catalytic domain of CKI is composed of two lobes with a cleft b etween them for binding ATP. Comparison of the mammalian and yeast CKI structures suggests that a rotation of the N-terminal domain occurs u pon ATP binding. This domain motion is similar, but not identical, to that observed in cAMP-dependent protein kinase upon binding ATP. Altho ugh Cki1 has many similarities to CKI delta over the catalytic domain, these two forms of CKI likely perform different functions in vivo. Re lating the primary sequences of other CKI enzymes to the three-dimensi onal architecture of CKI delta reveals a catalytic face that is especi ally conserved among the subset of CKI family members associated with the regulation of DNA repair. (C) 1996 Academic Press Limited