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Joined 2026-09-21 Message
Incoming links: CDK-activating kinase
CDK1 phosphorylation state 2026-10-14
A CDK1 phosphorylation state identifies modified amino acid residues. Different sites have opposite effects: in studied Xenopus laevis Cdc2, Thr14/Tyr15 are inhibitory, while Thr161 phosphorylation is activating. T denotes a threonine residue, Y a tyrosine residue, and numbers are protein primary structure positions. Do not assume this numbering for every species.[ref]
Role of phosphorylation in p34cdc2 activation: identification of an activating kinase by M. J. Solomon and others. Solomon, Lee and Kirschner (1992), abstract: mapped Xenopus Thr14/Tyr15, loss of activation with Thr161→Ala, and cyclin binding by the triple mutant
The 1992 study supplies a useful separation of mechanisms: replacing Thr14, Tyr15 and Thr161 still permitted cyclin B binding, but replacing Thr161 prevented activation of histone H1 phosphorylation. Binding therefore did not suffice for catalytic activity in that preparation. Activating phosphorylation also occurred with catalytically inactive Cdc2, supporting a separate CDK-activating kinase rather than a requirement for intramolecular autophosphorylation.[ref]
Role of phosphorylation in p34cdc2 activation: identification of an activating kinase by M. J. Solomon and others. Solomon, Lee and Kirschner (1992), abstract: cyclin-binding triple mutant and activating phosphorylation of the kinase-inactive K33R mutant
In this deliberately coarse classification, bound cyclin B, activating phosphorylation, and cleared inhibitory sites must coincide for the activity-permissive state. Removing inhibitory phosphate groups does not supply missing cyclin B or activating phosphorylation. Conversely, adding activating phosphorylation does not erase inhibitory modification. Actual preparations contain mixtures of states and additional regulators; this classification gives no numerical reaction rate.
CDK-activating kinase 2026-10-14
A CDK-activating kinase is a protein kinase supplying activating phosphorylation to a cyclin-dependent kinase 1 preparation. The Xenopus laevis experiment above distinguished this activity from the catalytic activity of Cdc2 itself. CAK names that function here, without asserting that every species uses the same protein assembly.