Cdk-activating kinase

The Cdk-activating Kinase (CAK) is a protein belonging to the kinase family of enzymes and plays a vital role in the regulation of the eukaryotic cell cycle. As its name suggests, the CAK performs its function by phosphorylating the Cdk protein (see Cyclin dependent kinases), rendering it fully active to perform its respective fucntion in regulating the cell cycle. Once a Cdk is partially activated by binding to a cyclin molecule, the CAK phosphorylates a threonine residue on a specific part of the Cdk called the T-loop. This T-loop partially blocks the substrate binding site on the Cdk and this phosphorylation causes the T-loop to undergo a small conformational change, revealing the active site and allowing the Cdk to bind to its substrates more efficiently.