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. 2015 Mar 23;9:98. doi: 10.3389/fnins.2015.00098

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Copyright © 2015 Maeda.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Biosynthesis of glycosaminoglycans. (A) Chondroitin sulfate (CS) and heparan sulfate (HS) chains are covalently attached to the proteoglycan core proteins through a common linkage tetrasaccharide. It is considered that the biosynthesis of a chondroitin chain starts with the addition of an N-acetylgalactosamine (GalNAc) residue to the linkage tetrasaccharide by CS N-acetylgalactosaminyltransferases (CSGalNAcT1, 2). After that, glucuronic acid (GlcA) and GalNAc residues are co-polymerized by chondroitin sulfate synthases (CHSY-1, -2, -3) and chondroitin polymerization factor (CHPF). When an N-acetylglucosamine (GlcNAc) residue is added to the linkage tetrasaccharide instead of GalNAc by EXTL 2 or 3, a heparan chain is polymerized by EXT family members. (B) After polymerization, they are modified by sulfation and epimerization reactions by many glycosaminoglycan modifying enzymes.