Unique sulfated polysaccharides from ascidians (Chordata, Tunicata)

Unique sulfated polysaccharides have been identified in ascidian tissues. A high-molecular-weight sulfated L-galactan consisting mainly of alpha-L-galactopyranose glycosidically linked through positions 1-->4, and sulfated at carbon 3 is present in the tunic of all species studied. Methylation, periodate oxidation, as well as 1H and 13C NMR analysis revealed that despite their homogeneous chemical composition, these L-galactans differ in type of glycosidic linkage, number of branches, and in the extent and position of sulfation. These L-galactans are synthesized by epidermal cells that epimerize D-glucose, possibly from a trehalose precursor, into L-galactose. In addition, a dermatan sulfate composed of a backbone of repeating [4-alpha-L-IdoA-1-->3-beta-D-GalNAc-1]n units similar to mammalian dermatan sulfate, but differing in the extent and position of sulfation has been isolated from the body of the ascidian, Ascidia nigra. Degradation of the ascidian dermatan with specific glycosidases and sulfatases, together with 1H and 13C NMR data, indicated that the disaccharide units are sulfated at the 2-position of alpha-L-induronate residues and at the 6-position of the N-acetyl-beta-D-galactosamine units. In contrast to mammalian dermatan sulfate, the ascidian molecule has no discenrible anticoagulant activity, as measured by the APTT assay, and has a low ability to potentiate heparin cofactor II. These data suggest that the 4-O-sulfation of N-acetyl-beta-D-galactosamine residues is essential for the anticoagulant activity of dermatan sulfate polymers.