Structural variations in the glycosaminoglycan-protein linkage region of recombinant decorin expressed in Chinese hamster ovary cells

Abstract

Decorin is a small fibroblast proteoglycan consisting of a core protein and a single chondroitin/dermatan sulfate chain. The structure of the carbohydrate-protein linkage region of the recombinant decorin expressed in Chinese hamster ovary cells was investigated. The decorin was secreted in the culture medium and isolated by anion-exchange chromatography. The glycosaminoglycan chain was released from the decorin by beta-elimination using alkaline NaBH4, and then digested with chondroitinase ABC. These treatments resulted in a major and a few minor hexasaccharide alditols derived from the carbohydrate-protein linkage region. Their structures were analyzed by enzymatic digestion in conjunction with high-performance liquid chromatography. Two of these compounds have the conventional hexasaccharide core, deltaHexA alpha1-3GalNAc beta1-4GlcA beta1-3Gal beta1-3Gal beta1-4Xyl-ol. One is nonsulfated, and the other is monosulfated on C4 of the GalNAc residue. They represent 12% and 60% of the total linkage region, respectively. The other compound has the hexasaccharide alditol with an internal iduronic acid residue deltaHexA alpha1-3GalNAc(4-sulfate)beta1-4IdoA alpha1-3Gal beta1-3Gal beta1-4Xyl-ol, which was previously demonstrated in one of the five linkage hexasaccharide alditols isolated from dermatan sulfate proteoglycans of bovine aorta (Sugahara et al., J. Biol. Chem., 270, 7204-7212, 1995). The compound accounts for 11% of the total linkage region. These structural variations in the linkage hexasaccharide region of the decorin strikingly contrast to the uniformity demonstrated in the linkage hexasaccharide structure of human inter-alpha-trypsin inhibitor (Yamada et al., Glycobiology, 5, 335-341, 1995) and urinary trypsin inhibitor (Yamada et al., Eur. J. Biochem., 233, 687-693, 1995), both of which have a single chondroitin sulfate chain with a uniform linkage hexasaccharide structure, deltaHexA alpha1-3GalNAc(4-sulfate)beta1-4GlcA beta1-3Gal(4-sulfate)beta1-3Gal beta1-4Xyl, containing a 4-O-sulfated Gal residue.