Regulatory Mechanism of 2-O-Phosphorylation of Xylose in the Glycosaminoglycan-Linkage Region of the Tetrasaccharide

Abstract

Glycosaminoglycans (GAGs) such as chondroitin sulfates and heparan sulfates are linear polysaccharide chains that are covalently attached to multiple core proteins to form proteoglycans (PGs). GAG chain assembly begins with the synthesis of common protein linkage region tetrasaccharide (glucuronic acid-galactose-galactose-xylose; GlcA-Gal-Gal-Xyl); this linkage region tetrasaccharide is attached to specific serine residues of core proteins. The GAG-protein linkage region tetrasaccharide of PGs transiently exhibited 2-O-phosphorylation of xylose. We identified a Xyl kinase that phosphorylates C-2 of the xylose residue and phosphoxylose phosphatase. This review focuses on the biological significance of phosphorylation and dephosphorylation of Xyl residues in the linkage region tetrasaccharide of PGs.