Autokinases

An autokinase is a type of enzyme that can catalyze the phosphorylation of its own amino acid residues using ATP as the phosphate donor. The term is often applied to kinases that regulate signaling pathways by autophosphorylation, thereby modulating their catalytic activity or creating binding sites for other signaling proteins.

Autophosphorylation can occur in cis (within the same molecule) or in trans (between two subunits in a dimer). In prokaryotes, histidine kinases of two-component systems autophosphorylate on a conserved histidine residue and then transfer the phosphate to a response regulator. In many eukaryotic receptor tyrosine kinases, autophosphorylation on tyrosine residues after ligand-induced dimerization creates docking sites for SH2, PTB, or other domains, propagating downstream signaling.

Activation is generally regulated by sensory domains or the oligomeric state; environmental cues (nutrients, osmolarity, growth factors) promote dimerization or conformational changes that enable autophosphorylation. Autokinases can function as initial steps in phosphorylation cascades, either directly triggering downstream kinases or enabling phosphotransfer to other proteins.

Examples include bacterial histidine kinases such as CheA and EnvZ, and eukaryotic receptor tyrosine kinases like EGFR and the insulin receptor. Aberrant autophosphorylation is implicated in diseases such as cancer and in bacterial pathogenicity when signaling becomes dysregulated.