Tyrosine sulfation

Tyrosine sulfation is a posttranslational modification where a sulfate group is added to a tyrosine residue of a protein molecule. Secreted proteins and extracellular parts of membrane proteins that pass through the Golgi apparatus may be sulfated. Sulfation was first discovered by Betteheim in bovine fibrinopeptide B in 1954 and later found be present in animals and plants but not in prokaryotes or in yeast.

Function
Sulfation plays role in strengthening protein-protein interactions. Types of human proteins known to undergo tyrosine sulfation include adhesion molecules, G-protein-coupled receptors, coagulation factors, serine protease inhibitors, extracellular matrix proteins, and hormones. Tyrosine O-sulfate is a stable molecule and is excreted in urine in animals. No enzymatic mechanism of tyrosine sulfate desulfation is known to exist.

By knock-out of TPST genes in mice, it may be observed that Tyrosine sulfation has effects on the growth of the mice, such as body weight, fecundity, and postnatal viability.

Mechanism
Sulfation is catalyzed by tyrosylprotein sulfotransferase (TPST) in Golgi apparatus. The reaction catalyzed by TPST is a transfer of sulfate from the universal sulfate donor 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to the side-chain hydroxyl group of a tyrosine residue. Sulfation sites are have a tyrosine residues exposed on the surface of the protein typically surrounded by acidic residues, a detailed description of the characteristics of the sulfation site is available from PROSITE (PROSITE pattern: PS00003). Two types of tyrosylprotein sulftotransferases (TPST-1 and TPST2) have been identified.

Regulation
There is very limited evidence that the TPST genes are subject to transcriptional regulation and tyrosine O-sulfate is very stable and cannot be easily degraded by mammalian sulfatases. Tyrosine O-sulfation is an irreversible process in vivo.