The six machines
CDK2 (CDK1-class Ser/Thr kinase)
ATP + protein-Ser/Thr → ADP + protein-Ser/Thr-P
Cyclin-activated Ser/Thr kinase that drives S phase. In-line phosphoryl transfer; the T-loop and cyclin binding order the active cleft.
EC 2.7.11.22 · PDB 1QMZ
▶ OPEN SIMULATORCDK7 (CDK-activating kinase)
ATP + CDK T-loop-Thr → ADP + CDK-Thr-P
The activating kinase of the CDK family: it phosphorylates the T-loop threonine that CDK2 needs to switch on.
EC 2.7.11.23 · PDB 1UA2
▶ OPEN SIMULATORWee1 (inhibitory Tyr kinase)
ATP + CDK-Tyr15-OH → ADP + CDK-Tyr15-P
Puts the inhibitory phosphate on CDK Tyr15 to hold the cycle at the G2/M checkpoint. Atypical tyrosine kinase (EC 2.7.10).
EC 2.7.10.2 · PDB 1X8B
▶ OPEN SIMULATORCdc25 (dual-specificity)
CDK-pTyr15 + H₂O → CDK-Tyr15 + Pᵢ
Erases Wee1's inhibitory mark to fire the G2/M transition. Cys-based dual-specificity phosphatase; a Cys-phosphate intermediate turns over through water.
EC 3.1.3.48 · PDB 1QB0
▶ OPEN SIMULATORPP2A (PPP2CA, metal phosphatase)
protein-pSer + H₂O → protein-Ser + Pᵢ
Broad Ser/Thr protein phosphatase that reverses kinase marks across the cycle. Two-metal (di-Mn) centre activates the water.
EC 3.1.3.16 · PDB 2IE4
▶ OPEN SIMULATORSeparase (ESPL1 / separin)
RAD21 (kleisin) cleaved at one site
Cysteine protease that cuts the cohesin kleisin RAD21 at anaphase, releasing sister chromatids. Not a phosphatase — a one-cut protease.
EC 3.4.22.49 · PDB 7NJ1
▶ OPEN SIMULATOR