Sulfated fucans and a fucosylated chondroitin sulfate are the major sulfated polysaccharides described in tissues of echinoderms. The connective tissue of the sea cucumber contams high amounts of a fucosylated chondroitin sulfate. This polysaccharide has a chondroitin sulfate-like structure, containing large numbers of sulfated α-L-fucopyranose branches linked to position 3 of the β-D-glucuronic acid residues. Methylation analysis and NMR spectroscopy revealed that the position of the glycosidic linkage and the site of sulfation in the fucose branches are heterogeneous. We proposed a preponderance of disaccharide units formed by 3, 4-di-
O-sulfo-α-L-fucopyranosyl units glycosidically linked through position l→2to 4-
O-sulfo-α-L-fucopyranose. These unusual fucose branches in the sea cucumber glycosaminoglycan obstruct the access of chondroitinases and hyaluronidases to the chondroitin sulfate core. We speculate that the fucose branches may prevent digestion of the sea cucumber body wall by microorganisms present in the marine environment.
The sulfated fucans from echinoderms have a tetrasaccharide repeat unit in which the separate residues are 1→3-linked α-L-fucopyranose but with difference in the extent and positions of their sulfate substitution. The sea urchin fucan has the structure:
[3-α-L-Fuc
p-2(OSO
3)-1→3-α-L-Fuc
p-4(OSO
3)-1→3-α-L-Fuc
p-2, 4(OSO
3)-1→3-α-L-Fuc
p-2(OSO
3)-1]n
and the sea cucumber has the structure:
[3-α-L-Fuc
p-2, 4(OSO
3)1→3-α-L-Fuc
p-1→3-α-L-Fuc
p-2(OSO
3)-1→3-α-L-Fuc
p-2(OSO
3)-1]n
This type of regular structure has not previously been described, and is in contrast with the random arrangement of substituents on the similar 1→3-linkedα-L-fucopyranose backbone of the sulfated fucans from brown algae.
The sulfated polysaccharides described in echinoderms share characteristics with the animal glycosaminoglycans and with the marine algae sulfated polysaccharides. This observation raises interesting questions concerning the evolutionary aspects of these macromolecules. In addition, the sulfated polysaccharides from echinoderms may be important to design new approach to the biological activities or to industrial applications of biopolymers.
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