HIGH-RESOLUTION CRYSTAL-STRUCTURES OF HUMAN CYCLIN-DEPENDENT KINASE-2WITH AND WITHOUT ATP - BOUND WATERS AND NATURAL LIGAND AS GUIDES FOR INHIBITOR DESIGN

Inhibition of the cell cycle is widely considered as a new approach to ward treatment for diseases caused by unregulated cell proliferation, including cancer. Since cyclin-dependent kinases (CDKs) are key enzyme s of cell cycle control, they are promissing targets for the design an d discovery of drugs with antiproliferative activity. The detailed str uctural analysis of CDK2 can provide valuable information for the desi gn of new ligands that can bind in the ATP binding pocket and inhibit CDK2 activity. For this objective, the crystal structures of human CDK 2 apoenzyme and its ATP complex were refined to 1.8 and 1.9 Angstrom, respectively. The high-resolution refinement reveals 12 ordered water molecules in the ATP binding pocket of the apoenzyme and five ordered waters in that of the ATP complex. Despite a large number of hydrogen bonds between ATP-phosphates and CDK2, binding studies of cyclic AMP-d ependent protein kinase with ATP analogues show that the triphosphate moiety contributes little and the adenine ring is most important for b inding affinity. Our analysis of CDK2 structural data, hydration of re sidues in the binding pocket of the apoenzyme, flexibility of the liga nd, and structural differences between the apoenzyme and CDK2-ATP comp lex provide an explanation for the results of earlier binding studies with ATP analogues and a basis for future inhibitor design.