Phosphorylated

Phosphorylated describes a molecule that contains a phosphate group covalently bound to it, typically through a phosphate ester linkage. In biology, phosphorylation is a reversible post-translational modification in which a phosphate group is added to a substrate by kinases and removed by phosphatases. The most common targets in eukaryotic proteins are serine, threonine, and tyrosine residues; in bacteria and some other organisms, histidine and aspartate can also be phosphorylated in signaling and metabolic processes.

The phosphorylation reaction uses ATP as the common phosphate donor, though other phosphate sources exist in certain pathways. The addition of a negatively charged phosphate group often induces conformational changes, alters catalytic activity, changes protein interactions, or modifies subcellular localization. As a result, phosphorylation acts as a molecular switch that can rapidly regulate signaling pathways, metabolism, cell growth, and gene expression.

In signaling networks, phosphorylation enables cascades that transmit and amplify cellular responses, such as receptor-mediated signaling and MAP kinase pathways. In metabolism, phosphorylation can activate or inhibit enzymes, thereby controlling flux through metabolic pathways. In bacteria, two-component systems commonly employ histidine kinases to transfer phosphate to response regulators, adjusting gene expression in response to environmental stimuli.

Disruption of normal phosphorylation balance is linked to various diseases and disorders. Phosphorylated proteins and peptides are widely studied in proteomics to understand cellular regulation and to identify potential therapeutic targets.