The structure of a trisialyl di-antennaryN-type glycopeptide obtained from rat plasma hemopexin

Rat hemopexin is a plasma glycoprotein that contains 18.3% carbohydrate consisting of onlyN-glycosidically-linked oligosaccharide chains. Glycopeptides obtained from hemopexin by Pronase^® digestion could be separated on Concanavalin A-Sepharose into three fractions. The lectin-binding fraction has been characterized as a mixture of monosialyl and disialyl di-antennary compounds ending inN-acetylneuraminic acid residues (2-6)-linked to galactose in the respective branches Bernard N, Lombart C, Strecker G, Montreuil J, Van Halbeek H, Vliegenthart JFG (1983) Biochimie 65:185–92].The structures of the glycans in the Concanavalin A non-binding fractions were determined by a combination of methylation analysis and 500-MHz¹H-NMR spectroscopy. Some of them appeared to be tri-antennary glycans. However, the major component of these fractions possesses the following structure: This type of structure has been encountered before in some bovine blood coagulation factors as well as in rat -acid glycoprotein, but the¹H-NMR parameters for it are first reported here. Furthermore, by methylation analysis, the occurrence of the NeuAc2-8NeuAc disaccharide element was demonstrated in a minor part of the carbohydrate moiety of rat hemopexin. This element has also been reported previously for rat brain glycopeptides.