CDKentsyymit

CDKentsyymit, or cyclin-dependent kinases (CDKs), are a family of conserved serine/threonine protein kinases in eukaryotic cells. Their catalytic activity depends on association with regulatory cyclin proteins. In the absence of cyclins, most CDKs are largely inactive; binding to a specific cyclin induces conformational changes that enable substrate recognition and activation. Activation is further governed by phosphorylation events and by inhibitors that modulate activity.

In humans, CDKs include several members with distinct roles. CDK1, in complex with cyclin B, drives the entry into mitosis. CDK2 paired with cyclins E and A regulates the G1/S transition and S phase progression. CDK4 and CDK6, with cyclins D, promote progression through G1 and the phosphorylation of the retinoblastoma protein, enabling DNA replication. CDK7 acts as a CDK-activating kinase and is part of the TFIIH transcription factor complex; CDK9, in association with cyclin T, participates in transcription elongation as part of P-TEFb. Other CDKs contribute to transcription, chromatin dynamics, or other cellular processes. The precise roles of CDKs can vary among organisms, but their core function as regulators of cell cycle and transcription is conserved.

Regulation of CDKs involves activation by phosphorylation of a key threonine residue in the activation loop by CDK-activating kinases, inhibition by CDK inhibitors such as p21, p27, p16, and periodic degradation of cyclins that drives cycles of activation and inactivation. Dysregulation of CDKs is common in cancer, leading to unchecked proliferation. Therapeutic inhibitors targeting CDKs, notably CDK4/6 inhibitors like palbociclib, ribociclib, and abemaciclib, are used in cancer treatment, though resistance and side effects pose challenges.