Structure of glycosaminoglycan (GAG)-linkage tetrasaccharide, GluAβ1,3Galβ1,3Galβ1,4Xylβ-O-serine and HS; (A) HS structure; (B) Sulfation of sugar residues; (C) Synthesis and localization of HS in host cells. Glycosyltransferases involved in GAG synthesis include (i) GlcAT-II (glucuronosyltransferase) and (ii) GlcNAcT-II (N-acetylglucosaminyltransferase II) for heparan sulfate synthesis. β-D-glucuronic acid (GlcA), α-L-iduronic acid (IdoA) and 2-O-sulfo-α-L-iduronic acid (IdoA(2S) are composed [124].