STRUCTURE OF THE PHOSPHORYLATED FORM OF THE CDK2:CYCLIN-A COMPLEX. Philip D. Jeffrey, Alicia A. Russo, Nikola P. Pavletich Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA

Progression through the eukaryotic cell cycle is controlled by the cyclin-dependent kinases (CDKs), which are in turn under the control of multiple levels of regulation. The isolated CDK is inactive, becoming partially activated upon binding of the corresponding cyclin subunit. Full activation of the kinase complex is achieved upon phosphorylation at a site on the CDK subunit (Thr 160 in CDK2).

We have previously determined the structure of a CDK2:CyclinA complex in its unphosphorylated state at 2.3 Angstrom resolution (ref. 1). Comparison of the CDK2 subunit with the structure of the uncomplexed CDK2 (ref. 2) revealed extensive conformational changes in two regions (the PSTAIRE helix and activation loop). In contrast, comparison of the cyclinA subunit with the uncomplexed cyclinA structure (ref. 3) did not indicate any conformational change on complex formation.

Subsequently, we have crystallized the fully active complex containing CDK2 that was phosphorylated at Thr 160. The structure of this complex reveals further conformational changes caused by phosphorylation. The contribution of these changes to the full activation of the kinase will be discussed.

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