Kinetic Mechanism of Activation of the Cdk2/Cyclin A Complex

• Published in: The Journal of biological chemistry Vol. 277; no. 26; pp. 23847 - 23853
• Main Authors: Morris, May C., Gondeau, Claire, Tainer, John A., Divita, Gilles
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 28.06.2002; American Society for Biochemistry and Molecular Biology
• Subjects: Biochemistry; Biochemistry, Molecular Biology; CDC2-CDC28 Kinases; Cyclin A / chemistry; Cyclin-Dependant Kinases / chemistry; Life Sciences; Protein-Serine-Threonine Kinases / chemistry; Structural Biology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M107890200

Eukaryotic cell cycle progression is controlled by the ordered action of cyclin-dependent kinases, activation of which occurs through the binding of the cyclin to the Cdk followed by phosphorylation of a conserved threonine in the T-loop of the Cdk by Cdk-activating kinase (CAK). Despite our understanding of the structural changes, which occur upon Cdk/cyclin formation and activation, little is known about the dynamics of the molecular events involved. We have characterized the mechanism of Cdk2/cyclin A complex formation and activation at the molecular and dynamic level by rapid kinetics and demonstrate here that it is a two-step process. The first step involves the rapid association between the PSTAIRE helix of Cdk2 and helices 3 and 5 of the cyclin to yield an intermediate complex in which the threonine in the T-loop is not accessible for phosphorylation. Additional contacts between the C-lobe of the Cdk and the N-terminal helix of the cyclin then induce the isomerization of the Cdk into a fully mature form by promoting the exposure of the T-loop for phosphorylation by CAK and the formation of the substrate binding site. This conformational change is selective for the cyclin partner.