Figure 3.

Initially, the EXT (exostosin) family of enzymes are responsible for heparan sulfate (HS) chain initiation and elongation from the serine residue (S) on a core protein. Deacetylation and sulfation of HS is performed by the NDST (N-deacetylase/N-sulfotransferase) family of enzymes. Enzymatic activity of GLCE (d-glucuronyl C5-epimerase) results in epimerization of glucuronic acid to iduronic acid on the HS chain. Finally, the HSxST family of enzymes (heparan sulfate O-sulfotransferases; x = 2, 3, or 6) catalyzes additional sulfation of the HS chain on C2, C3, and C6, respectively, within the NS domains.