How do cyclins activate cdk?
A cyclin forms a complex with Cdk. Complex formation results in activation of the Cdk active site. When concentrations in the cell are low, cyclins dissociate from Cdk, thus inhibiting enzymatic activity; this probably occurs due to a protein chain of the Cdk blocking the active site upon cyclin dissocation. Cyclins themselves have no enzymatic activity. Cyclins, when bound with the dependent kinases, such as the p34 (cdc2) or cdk2 proteins, form the maturation promoting factor. MPFs activate other proteins through phosphorylation. These phosphorylated proteins in turn are responsible for specific events during cycle division such as microtubule formation and chromatin remodeling.
