Cyclin-dependent kinases (CDKs) are the master regulators of the eukaryotic cell cycle. To become activated, CDKs require both regulatory phosphorylation and binding of a cognate cyclin subunit. We studied the activation process of the G1/S kinase Cdk2 in solution and developed a thermodynamic model that describes the allosteric coupling between regulatory phosphorylation, cyclin binding and inhibitor binding. The results explain why monomeric Cdk2 lacks activity despite sampling an active-like state, reveal that regulatory phosphorylation enhances allosteric coupling with the cyclin subunit and show that this coupling underlies differential recognition of Cdk2 and Cdk4 inhibitors. We identify an allosteric hub that has diverged between Cdk2 and Cdk4 and show that this hub controls the strength of allosteric coupling. The altered allosteric wiring of Cdk4 leads to compromised activity toward generic peptide substrates and comparative specialization toward its primary substrate retinoblastoma (RB). [Figure not available: see fulltext.]
Bibliographical noteFunding Information:
We thank M. Young for the Cdk2 and yeast CAK constructs, J. Endicott for the bovine cyclinA construct and S. Rubin for the RB771–928 construct. We thank J. Dalluge for assistance with mass spectrometry. This work was supported in part by grants from the National Institutes of Health (no. R01 GM121515, N.M.L.) and the National Institutes of Health Cancer Biology Training grant (no. T32 CA009138, A.M.) and Chemistry-Biology Interface Training grant (no. T32 GM132029, D.M.R.).
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