The crystal structure of the human cyclinA-cyclin-dependent kinase2 (C
DK2)-ATP complex has been determined at 2.3 Angstrom resolution. Cycli
nA binds to one side of CDK2's catalytic cleft, inducing large conform
ational changes in its PSTAIRE helix and T-loop. These changes activat
e the kinase by realigning active site residues and relieving the ster
ic blockade at the entrance of the catalytic cleft.