transphosphorylation

Transphosphorylation is the biochemical process in which a phosphate group is transferred from a donor molecule to an acceptor molecule. It is most commonly mediated by kinases or phosphotransferases. In cells, the phosphate donor is often ATP, which donates the γ-phosphate, but other donors such as GTP or phosphorylated intermediates can participate depending on the enzyme and pathway.

In cellular signaling, transphosphorylation typically refers to phosphorylation of a target molecule by a different enzyme, i.e., a phosphorylation event between distinct proteins. This is distinct from autophosphorylation, where the same molecule both donates and receives the phosphate. Phosphorylation can regulate protein activity, interactions, localization, and stability, enabling complex signal transduction.

Common examples include receptor tyrosine kinases, which undergo transphosphorylation of their cytoplasmic kinase domains upon ligand-induced dimerization, creating docking sites for downstream signaling proteins. In bacterial two-component systems, a histidine kinase autophosphorylates and then transfers the phosphate to a response regulator in a transphosphorylation reaction. Transphosphorylation can also occur between different serine/threonine or tyrosine kinases within signaling cascades.

Terminology can vary by context, but the core concept remains a phosphate transfer from one molecule to another, typically catalyzed by a kinase or related enzyme. The process is central to numerous cellular pathways, including metabolism, cell growth, and environmental sensing.