Catalytic domain of Cyclin-Dependent protein Kinase 1-like Serine/Threonine Kinases and of Plant B-type Cyclin-Dependent protein Kinase
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. This subfamily is composed of CDK, CDK2, and CDK3. CDK1 is also called Cell division control protein 2 (Cdc2) or p34 protein kinase, and is regulated by cyclins A, B, and E. The CDK1/cyclin A complex controls G2 phase entry and progression while the CDK1/cyclin B complex is critical for G2 to M phase transition. CDK2 is regulated by cyclin E or cyclin A. Upon activation by cyclin E, it phosphorylates the retinoblastoma (pRb) protein which activates E2F mediated transcription and allows cells to move into S phase. The CDK2/cyclin A complex plays a role in regulating DNA replication. Studies in knockout mice revealed that CDK1 can compensate for the loss of the cdk2 gene as it can also bind cyclin E and drive G1 to S phase transition. CDK3 is regulated by cyclin C and it phosphorylates pRB specifically during the G0/G1 transition. This phosphorylation is required for cells to exit G0 efficiently and enter the G1 phase. The plant-specific B-type CDKs are expressed from the late S to the M phase of the cell cycle. They are characterized by the cyclin binding motif PPT[A/T]LRE. They play a role in controlling mitosis and integrating developmental pathways, such as stomata and leaf development. CdkB has been shown to associate with both cyclin B, which controls G2/M transition, and cyclin D, which acts as a mediator in linking extracellular signals to the cell cycle. CDKs belong to a large family of STKs that are regulated by their cognate cyclins. Together, they are involved in the control of cell-cycle progression, transcription, and neuronal function. The CDK1 subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
Jiyao W et al.(2023). "The conserved domain database in 2023.",