Fig. 1

Structure and biosynthesis of HS. a – The structure of the repeating disaccharide unit in HS. The polysaccharide backbone of HS is composed of an alternating repeat of GlcA/IdoA and D-glucosamine (GlcN): -4GlcAβ/IdoAα1-4GlcNα1-. The amino group of GlcN is acetylated or sulfated. Hydroxy groups at the C6 of GlcN and the C2 of GlcA/IdoA may be sulfated. The hydroxy group of the C3 position (indicated by an asterisk) of N-sulfated/N-unsubstituted GlcN residue in specific saccharide sequences is possibly sulfated. b – A schematic drawing of the structure of HS polysaccharides. The enzyme responsible for the transfer of each monosaccharide residue is shown below the corresponding sugar residue. Gene(s) encoding each enzyme are also shown below. The arrow indicates the direction of biosynthesis. XylT, xylosyltransferase; GalT-I, galactosyltransferase I; GalT-II, galactosyltransferase II; GlcAT-I, glucuronyltransferase I; GlcAT-II, glucuronyltransferase II; GlcNAcT-I, GlcNAc transferase I; GlcNAcT-II, GlcNAc transferase II