Structural studies on sulfated glycopeptides from the carbohydrate-protein linkage region of chondroitin 4-sulfate proteoglycans of swarm rat chondrosarcoma. Demonstration of the structure Gal(4-O-sulfate)β1-3Galβ1-4Xylβ1-O-Ser

Abstract

Nonsulfated, monosulfated, and disulfated glycopeptides containing the entire carbohydrate sequence of the glycosaminoglycan-specific linkage region were isolated after exhaustive enzymatic digestions of Swarm rat chondrosarcoma proteoglycans with chondroitinase ABC, papain, and Pronase. Their structures were examined by 500 MHz 1H NMR spectroscopy. The nonsulfated compound has the following structure with trace amounts of a few additional amino acids: delta 4,5-GlcAβ1-3GalNAcβ1- 4GlcAβ 1-3Galβ 1-3Galβ 1-4Xylβ 1-O-Ser. The monosulfated compound has an ester sulfate on C-4 of the GalNAc residue and the disulfated compound has an additional hitherto unrecognized ester sulfate on C-4 of the second galactose residue which is remote from the innermost xylose. This new structure was confirmed by two- dimensional homonuclear Hartmann-Hahn spectroscopy. The molar ratio of the isolated nonsulfated, monosulfated, and disulfated compounds was 53:37:10 based on the serine contents. Biological significance of the newly found sulfated linkage structure is discussed.