– Protein-tyrosine sulfotransferase 1, also known as Tyrosylprotein sulfotransferase 1 and TPST1, is a single-pass type II membrane protein that belongs to the protein sulfotransferase family. Tyrosine O-sulfation is a common posttranslational modification of proteins in all multicellular organisms. This reaction is mediated by a Golgi enzyme activity called tyrosylprotein sulfotransferase (TPST) that catalyzes the transfer of sulfate from 3′-phosphoadenosine 5′-phosphosulfate to tyrosine residues within acidic motifs of polypeptides. Tyrosine O-sulfation has been shown to be important in protein-protein interactions in several systems. Tyrosine sulfation is mediated by one of two Golgi isoenzymes, called tyrosylprotein sulfotransferases (TPST-1 and TPST-2). A relatively small number of proteins are known to undergo tyrosine sulfation, including certain adhesion molecules, G-protein-coupled receptors, coagulation factors, serpins, extracellular matrix proteins, and hormones. TPST1 is a human tyrosylprotein sulfotransferase that uses 3’phosphoadenosine-5’phosphosulfate (PAPS) to transfer the sulfate moiety to proteins predominantly designated for secretion. TPST1 bears N-linked glycosyl residues exclusively at position Asn6 and Asn262. TPST1 and TPST2 have distinct biological roles that may reflect differences in their macromolecular substrate specificity.