Structural determination of five novel tetrasaccharides containing 3-O-sulfated D-glucuronic acid and two rare oligosaccharides containing a β-D-glucose branch isolated from squid cartilage chondroitin sulfate E

Oversulfated chondroitin sulfate E (CS-E) derived from squid cartilage exhibits intriguing biological activities, which appear to reflect the biological activities of mammalian CS chains containing the so-called E disaccharide unit [GlcAbeta1-3GalNAc(4,6-O-disulfate)]. Previously, we isolated novel tetra- and hexasaccharides containing a rare GlcA(3-O-sulfate) at the nonreducing end after digestion of squid cartilage CS-E with testicular hyaluronidase. In this study, squid cartilage CS-E was extensively digested with chondroitinase AC-II, which yielded five highly sulfated novel tetrasaccharides and two odd-numbered oligosaccharides (tri- and pentasaccharides) containing D-Glc. Their structures were determined by fast atom bombardment mass spectrometry and H-1 NMR spectroscopy. The results revealed an internal GlcA(3-O-sulfate) residue for all the novel tetrasaccharide sequences, which rendered the oligosaccharides resistant to the enzyme. The results suggest that GlcA(3-O-sulfate) units are not clustered but rather interspersed in the CS-E polysaccahride chains, being preferentially located in the highly sulfated sequences. The predominant structure on the nearest nonreducing side of a GlcA(3-O-sulfate) residue was GalNAc(4-O-sulfate) (80%), whereas that on the reducing side was GalNAc(4,6-O-disulfate) (59%). The structural variety in the vicinity of the GlcA(3-O-sulfate) residue might represent the substrate specificity of the unidentified chondroitin GlcA 3-O-sulfotransferase. The results also revealed a trisaccharide and a pentasaccahride sequence, both of which contained a beta-D-Glc branch at the C6 position of the constituent GalNAc residue. Approximately 5 mol % of all disaccharide units were substituted by Glc in the CS-E preparation used.