sulfotyrosine

Sulfotyrosine is a form of the amino acid tyrosine in which a sulfate group is covalently attached to the phenolic hydroxyl, yielding tyrosine-O-sulfate. In proteins, tyrosine sulfation is a common extracellular post-translational modification, occurring on secreted and membrane proteins within the secretory pathway rather than in the cytosol.

In eukaryotes, sulfation is carried out by tyrosylprotein sulfotransferases (TPST1 and TPST2) in the Golgi apparatus. These enzymes transfer a sulfate from the donor molecule 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to specific tyrosine residues, producing sulfated tyrosine. The modification is typically stable and occurs in particular extracellular regions of proteins, influencing their interaction with other molecules.

Biological roles of sulfotyrosine include modulation of protein-protein interactions and ligand recognition. Sulfated tyrosines are important for the binding of selectins to their ligands, such as PSGL-1, and can affect receptor-ligand binding and signaling in chemokine receptors and other cell surface proteins. The presence or absence of a sulfate group can alter binding affinity and specificity, contributing to processes like trafficking, adhesion, and immune responses.

Detection and use in research: Sulfotyrosine-containing peptides and proteins can be studied by mass spectrometry and specialized proteomic approaches, though the sulfate moiety can be labile under some analytical conditions. Synthetic chemistry provides protected sulfotyrosine derivatives (for example, Fmoc-sulfotyrosine) used to incorporate sulfated tyrosine into peptides and proteins for functional studies.

Sulfotyrosine is distinct from phosphotyrosine, representing a separate post-translational modification added in the Golgi rather than by cytosolic kinases, and is generally considered irreversible on cellular timescales.