Structure and Biosynthesis of Carbohydrate-Protein Linkage Region of Dermatan Sulfate and Chondroitin Sulfate

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The fine structure and the biosynthetic mechanisms of sulfated glycosamino-glycans are not fully understood. In this study, we carried out structural studies on the carbohydrate-protein linkage region of a dermatan sulfate preparation and various chondroitin sulfate preparations, and also studied putative biosynthetic enzymes.In the structural studies, we isolated five hexasaccharide alditols derived from the linkage region of bovine aorta dermatan sulfate chains after chondoritinase ABC digestion and beta-elimination reaction. The structures of the three of them were identical to those isolated previously from chondroitin 4-sulfate of whale cartilage. In contrast, the other two contained hitherto unreported structures including iduronic acid (IdoA) : DELTAHexAalpha1-3GalNAc (4-sulfate) beta1-4IdoAalpha1-3Gal (4-sulfate) beta1-3Galbeta1-4Xyl-ol and DELTAHexAalpha1-3GalNAc (4-sulfate) beta1-4IdoAalpha1-3Galbeta1-3Galbeta1-4Xyl-ol.We also isolated the following hexasaccharide as a sole linkage component from chondroitin 4-sulfate of inter alpha-trypsin inhibitor in human plasma and a trypsin inhibitor in human urine : DELTAHexAalpha1-3GalNAc (4-omicron-sulfate) beta1-4GlcAbeta1-3Gal (4-omicron-sulfate) beta1-3Galbeta1-4Xyl-ol. The results are taken to indicate the importance of the sulfated Gal structure in the biosynthesis of the linkage region.In the biosynthetic studies, we discovered a hitherto unreported alpha-GalNAc transferase activity in fetal bovine serum. It catalyzed a transfer of alpha-GlaNAc residue to GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-omicron-Ser, but not to GlcAbeta1-3Gal (4-omicron-sulfate) beta1-3Galbeta1-omicron-Ser. It remains to be investigated whether or not this enzyme is in involved indeed in the biosynthesis of chondroitin sulfate. In addition, we detected in fetal bovine serum a beta-GalNAc transferase activity that is involved in the synthesis of the repeating disaccharide region of chondroitin sulfate.