13C-NMR spectroscopy of keratan sulphates--assignments for five sialylated pentasaccharides derived from the non-reducing chain termini of bovine articular cartilage keratan sulphate by keratanase II digestion.

ABSTRACT

Skeletal keratan sulphate has been fragmented using the enzyme keratanase II, and 13C chemical-shift data are reported for five reduced sialylated pentasaccharides that derived from the non-reducing chain terminal region. They have the structures NeuAc(alpha2-6)Gal(beta1-4)GlcNAc6S(beta1-3)Gal(beta1-4)GlcNAc6 S-ol, NeuAc(alpha2-3)Gal(beta1-4)GlcNAc6S(beta1-3)Gal(beta1-4)GlcNAc6 S-ol, NeuAc(alpha2-6)Gal(beta1-4)GlcNAc6S(beta1-3)Gal6S(beta1-4)++ +GlcNAc6S-ol, NeuAc(alpha2-3)Gal(beta1-4)GlcNAc6S(beta1-3)Gal(6S)(beta1-4)Glc NAc6S-ol, and NeuAc(alpha2-3)Gal(6S)(beta1-4)GlcNAc6S(beta1-3)Gal(6S)(beta1-4)++ +GlcNAc6S-ol, where GlcNAc6S-ol represents N-acetyl-glucosaminitol 6-O-sulphate and NeuAc represents N-acetylneuraminic acid. The use of these 13C-NMR spectroscopy data for the recognition of specific chain-capping structures within native keratan sulphates is discussed. In addition, examination of the data derived from the NeuAc(alpha2-6) capping structures strongly suggests that sulphation three residues away from the neuraminic acid cap has a profound effect upon the conformation of the capping region.