CS is a long polysaccharide consisting of the repeating disaccharide units GlcA and N-acetyl-galactosamine (GalNAc), attached to serine residues of core proteins. The chains from eukaryotic organisms are extensively modified by sulfation, yielding six different disaccharides: GlcA-GalNac residues (O unit), GlcA-GalNAc-4-sulfate (A unit), GlcA-GalNAc-6-sulfate (C unit), GlcA-GalNAc-4,6-disulfated (E unit). The GlcA residue can also be sulfated at the 2-position giving rise to B units (GlcA-2-sulfated-GalNAc-4-sulfated) and D units (GlcA-2-sulfated-GalNAc-6-sulfated) 3. Even more complex sulfation patterns have been described in the invertebrate phyla 2.
