Structural characterization of immunostimulating protein-sulfated fucan complex extracted from the body wall of a sea cucumber, Stichopus japonicus.

The water soluble protein-sulfated fucan (PSF) complex isolated from the body wall of Stichopus japonicus was fractionated using an anion-exchange chromatography to obtain four purified fractions (F1, F2, F3, and F4) and to investigate their structural characteristics and immuno-enhancing activities. The crude PSF and fractions mostly consisted of neutral sugars, proteins and sulfates in various proportions. Fucose was their major monosaccharide unit with small portion of mannose, glucose and galactose. The molecular weight (Mw) of the crude PSF and fractions ranged from 323.6×103 to 3630.0×103g/mol. The crude PSF, F2, and F3 were potent stimulator of RAW264.7 cells inducing marked nitric oxide (NO) and cytokines production. The glycosidic linkage of polysaccharides was evaluated using GC-MS and confirmed by 2D-NMR. The main backbone of highly immunostimulating F3 fraction was (1→3)-α-l-linked fucosyl residue with sulfation at C-2 and/or C-4.