Extensive heterogeneity of proteoglycans bearing fucose-branched chondroitin sulfate extracted from the connective tissue of sea cucumber

The major sulfated polysaccharide in the sea cucumber body wall is a fucose-branched chondroitin sulfate. This glycosaminoglycan has side-chain disaccharide units of sulfated fucopyranosyl or sulfate esters linked to the O-3 position of the beta-D-glucuronic acid residues. These unusual fucose branches and sulfate esters block the access of chondroitinases to the chondroitin sulfate core [Vieira & Mourão (1988) J. Biol. Chem. 263, 18176-18183; Vieira et al. (1991) J. Biol. Chem. 266, 13530-13536]. We now report the isolation and preliminary characterization of the proteoglycans bearing this unique fucose-branched chondroitin sulfate. They were extracted using guanidine hydrochloride solutions containing protease inhibitors and were purified by anion-exchange and gel-filtration columns. Interestingly, the sea cucumber proteoglycans were cleaved by chondroitinase AC or ABC, indicating that the beta-D-glucuronic acid residues close to the reducing end of the polysaccharide chain are neither fucosylated nor sulfated. SDS-polyacrylamide gel electrophoresis revealed several fractions of proteoglycans of different molecular sizes but containing a similar hexuronic acid/protein ratio and a similar type of glycan chain. Possibly, the low-molecular-size fractions arise from a protease cleavage of a larger molecule. In contrast with the results observed for most vertebrate proteoglycans, which contain a single core protein for each type of proteoglycan, chondroitinase AC or ABC releases from the sea cucumber proteoglycans a wide variety of core proteins. These observations are the first detailed study of a proteoglycan from invertebrate tissue and reveal extensive heterogeneity when compared with proteoglycans from vertebrate connective tissue.