Structure determination for octasaccharides derived from the carbohydrate-protein linkage region of chondroitin sulphate chains in the proteoglycan aggrecan from bovine articular cartilage

Abstract

Five octasaccharides derived from the protein carbohydrate linkage region of chondroitin sulphate (CS) have been isolated from the large aggregating proteoglycan (aggrecan) extracted from the bovine articular cartilage of 6-year-old to 8-year-old animals. Following the purification of aggrecan the attached CS chains were digested with CS ABC endolyase and subsequently released from the protein core by β-elimination. The individual oligosaccharides were purified by strong anion-exchange chromatography and their structures determined by very high-field one-dimensional and two- dimensional 1H-NMR spectroscopy. They were found to be octasaccharides, comprised of tetrasaccharide repeat-region extensions to the core tetrasaccharide linkage region structure. They have the following structures: ΔUA(β1-3)GalNAc(β1-4)GlcA(β1-3)GalNAc(β1-4)GlcA(β1-3)Gal(β1-3)Gal(β1- 4)Xyl-ol, ΔUA(β1-3)GalNAc(β1-4)GlcA(β1-3)GalNAc6S(β1-4)GlcA(β1- 3)Gal(β1-3)Gal(β1-4)Xyl-ol, ΔUA(β1-3)GalNAc6S(β1-4)GlcA(β1- 3)GalNAc(β1-4)GlcA(β1-3)Gal(β1-3)Gal(β1-4)Xyl-ol, ΔUA(β1- 3)GalNAc6S(β1-4)GlcA(β1-3)GalNAc6S(β1-4)GlcA(β1-3)Gal(β1-3)Gal(β1- 4)Xyl-ol and ΔUA(β1-3)GalNAc4S(β1-4)GlcA(β1-3)GalNAc6S(β1-4)GlcA(β1- 3)Gal(β1-3)Gal(β1-4)Xyl-ol. They differ only in the nature of the sulphation of the GalNAc residues of the tetrasaccharide-repeat-region extension, which forms the first two disaccharides of the repeat region. No sulphation of any of the uronic acid residues has been identified and in one oligosaccharide neither of the GalNAc residues were sulphated. The majority of the linkage regions contained GalNAc residues which were fully 6- sulphated. However, in a significant amount, only one of the residues was 6- sulphated while the other was either unsulphated or 4-sulphated. There was no evidence either for sulphation of the linkage region galactose residues or for phosphorylation of the xylose residue, through which the chain is attached to the core protein.