Heparan Sulfate 3-O-Sulfotransferase 1/HS3ST1: ProductsHeparan sulfate is a highly sulfated polysaccharide that can be found on cell surface and within extracellular matrix. It is typically covalently attached to the protein core of proteoglycans, such as syndecans and glypicans. Heparin, on the other hand, can be considered as a highly sulfated version of heparan sulfate that is detached from the protein core and is predominantly found in mast cells. Both heparin and heparan sulfate contain disaccharide repeats of uronic acid and N-acetylglucosamine and are modified by the same sulfotransferases. The uronic acid residues can be sulfated at 2-O position by heparan sulfate 2-O sulfotransferase (HS2ST). The N-acetylglucosamine residues can be sulfated at N, 3-O, and 6-O positions by N-deacetylase/N-sulfotransferases (NDSTs), heparan sulfate 3-O sulfotransferases (HS3STs) and heparan sulfate 6-O sulfotransferases (HS6STs) respectively. There are seven HS3STs in the human genome. HS3ST1 is a rate-limiting enzyme for generating an antithrombin-binding pentasaccharide epitope on heparan sulfate and heparin. Unlike other sulfotransferases that have signal-anchor domains and are type II membrane integral proteins in Golgi apparatus, HS3ST1 lacks a transmembrane domain and is likely to be an intraluminal enzyme.