Structural Studies on the Carbohydrate-Protein Linkage Region of Proteoglycans

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From the carbohydrate-protein linkage region of whale cartilage proteoglycans, which bear predominantly chondroitin 4-sulfate, one nonsulfated, two monosulfated and one disulfated hexasaccharide alditols were isolated after exhaustive digestions with Actinase E and chondroitinase ABC and subsequent b-elimnination. Their structures were analyzed by chondroitinase ACII digestion in conjunction with HPLC and by 500 MHz ^1H-NMR spectroscopy. The nonsulfated compound (A) had the conventional structure : DELTAGlcAbeta1-3GalNAcbeta1-4GlcAbeta1-3Galbeta1-3Galbeta1-4Xyl-ol, while the other compounds were sulfated derivatives of the compound A. Two monosulfated compounds (B and C) had an ester sulfate on C-4 or C-6 of the GalNAc residue, respectively, and the disulfated compound (D) had two ester sulfate groups, namely, one on C-4 of the GalNAc and the other on C-4 of the Gal residue substituted by GlcA. The molar ratio of A : B : C : D was 0.21 : 0.16 : 0.36 : 0.27. The compound containing Gal- … More 4-omicron-sulfate structure was previously isolated by us in the form of sulfated glycoserine [DELTAGlcAbeta1-3GAlNAc(4-omicron-sulfate)beta1-4GlcAbeta1-3Gal(4-omicron-sulfate)beta1-3Galbeta1-4Xylbeta1-omicron-Ser] from the carbohydrate-protein linkage region of rat chondrosarcoma chondroitin 4-sulfate proteoglycans. The discovery of this structure in the carbohydrate-protein linkage region of chondroitin 4-sulfate proteoglycans from nontumorous cartilage indicates that it is not tumor-associated product but rather a physiological biosynthetic product since it represents a significant proportion.A preparation of porcine stage 14 intestinal heparin, which contains Ser as a predominant amino acid, was used for isolation of the carbohydrate-protein linkage region of heparin. Two glycoserines were isolated in a molar ratio of 96 : 4 after an exhaustive digestion with a mixture of bacterial heparinase and heparitinases. Their structures were determined by composition analysis, heparitinase digestion, co-chromatography with an authentic glycoserine on HPLC and by 500-MHz 1D and 2D ^1H-NMR spectroscopy. The structure of the major one is DELTAGlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-omicron-Ser and that of the minor is DELTAGlcAbeta1-4GlcNAc(6-omicron-sulfate)alpha1-4GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-omicron-Ser. The novel 6-omicron-sulfated GlcNAc residue was demonstrated to occur in the vicinity of the carbohydrate-protein linkage region. The Gal residues were nonsulfated, being in contrast to the sulfated Gal structures recently discovered in the carbohydrate-protein linkage region of chondroitin sulfate proteoglycans. Less