Figure 1.

Structures of the repeat units in various GAGs. (A) HA is an unsulfated polymer with [−4)-β-GlcUA-(1-3)-β-GlcNAc-(1-] as the repeating unit. (B) CS is the polymer of sulfated [−4)-β-GlcUA-(1-3)-β-GalNAc-(1-]. Depending on the sulfation pattern, CS can be classified into different subtypes (CSA, CSC, CSD, and CSE). (C) DS composes of the repeating dimeric unit [−4)-α-IdoUA-(1-3)-β-GalNAc-(1-]. L-IdoUA is an epimer of D-GlcUA and the GalNAc residue is sulfated at different positions similar to CS. (D) The major disaccharide unit of heparin is [−4)-α-IdoUA-(1-4)-α-GlcN-(1-]. Iduronic acid is sulfated at O2 and the GlcN unit is N- and O6-sulfated. (E) The major disaccharide unit of HS is [−4)-α-GlcUA-(1-4)-β-GlcNAc-(1-]. The GlcNAc residue is generally sulfated at N2 with or without O6 sulfation. (F) In the typical KS, disaccharide subunits are composed of Gal and GlcNAc-6-sulfate. The Gal residues may or may not have O6 sulfation.