Cyclin-dependent kinase
Phosphorylation

Unlike activating phosphorylation, CDK inhibitory phosphorylation is crucial for cell cycle regulation. Various kinases and phosphatases control their phosphorylation state. For instance, the activity of CDK1 is controlled by the balance between WEE1 kinases, Myt1 kinases, and the phosphorylation of Cdc25c phosphatases. Wee1, a kinase preserved across all eukaryotes, phosphorylates CDK1 at Tyr 15. Myt1 can phosphorylate both the threonine (Thr 14) and the tyrosine (Tyr 15). The dephosphorylation is performed by Cdc25c phosphatases, by removing the phosphate groups from both the threonine and the tyrosine. This inhibitory phosphorylation helps preventing cell-cycle progression in response to events like DNA damage. The phosphorylation does not significantly alter the CDK structure, but reduces its affinity to the substrate, thereby inhibiting its activity. For the cell cycle to progress, the inhibitory phosphate groups must be removed by the Cdc25 phosphatases to reactivate the CDKs.
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