phosphosubstrate

A phosphosubstrate is a molecule, typically a protein, that becomes modified by phosphorylation. In cellular signaling, kinases transfer a phosphate group from ATP to specific amino acid residues on their substrates, most commonly serine, threonine, or tyrosine. The term typically refers to the substrate of a kinase, rather than the kinase itself.

Phosphorylation can change a substrate’s activity, stability, conformation, localization, or interactions with other proteins. It often acts as a molecular switch that toggles signaling pathways on or off. Phosphorylation can create or block binding motifs for other proteins, such as SH2 domains or 14-3-3 proteins, thereby altering downstream signaling. Phosphosubstrates are counterbalanced by phosphatases, which remove phosphate groups and restore the resting state.

Examples of well-known phosphosubstrates include glycogen synthase, which is inhibited by phosphorylation from glycogen synthase kinase 3, and transcription factors such as CREB, phosphorylated by PKA to regulate gene expression. In cell-cycle control, a broad set of CDK substrates becomes phosphorylated to drive progression. Other substrates include transcription factors, metabolic enzymes, and cytoskeletal regulators, reflecting the broad reach of phosphorylation in cellular regulation.

Techniques to study phosphosubstrates include phosphoproteomics to map phosphorylation sites, phospho-specific antibodies for targeted detection, and in vitro kinase assays to confirm direct phosphorylation. Understanding phosphosubstrates is central to deciphering signaling networks and their roles in development, physiology, and disease.