autokinase

An autokinase is an enzyme that catalyzes the phosphorylation of a substrate that is part of the same molecule, typically the kinase itself, a process known as autophosphorylation. In many cases the kinase uses ATP as the phosphate donor. Autophosphorylation can regulate activity, localization, and interactions with other proteins.

Mechanisms of autophosphorylation include cis-autophosphorylation, where the kinase phosphorylates itself within the same polypeptide, and trans-autophosphorylation, where two kinase molecules phosphorylate each other. Trans-autophosphorylation is common in dimeric receptor kinases and in many histidine kinases involved in bacterial two-component signaling systems.

Classes and examples of autokinases span multiple kinase families. Receptor tyrosine kinases, such as the epidermal growth factor receptor, autophosphorylate on intracellular tyrosine residues upon ligand-induced dimerization, creating docking sites for downstream signaling proteins. Serine/threonine kinases may autophosphorylate within their activation loops to achieve full activity. Bacterial histidine kinases autophosphorylate on a histidine residue and then transfer the phosphate to a response regulator, often affecting gene expression and behavior.

Significance of autophosphorylation lies in its ability to activate kinases, regulate catalytic efficiency, and modulate interactions with other signaling components. Reversal of the modification by phosphatases resets the system, allowing dynamic control of signaling pathways.

See also: autophosphorylation; protein kinase; phosphorylation; two-component systems.