Structural characteristics and anti-complement activities of polysaccharides fromSargassum hemiphyllum

Three polysaccharides (SH-1, SH-2 and SH-3) were purified from a brown macroalgea,Sargassum hemiphyllum. The autohydrolysis products from each polysaccharide were separated to three fractions (S fractions as oligomers, L fractions as low molecular weight polysaccharides and H fractions as high molecular weight polysaccharides). Mass spectroscopy of S fractions (SH-1-S, SH-2-S and SH-3-S) showed that these three polymers all contained short stretches of sulfated fucose. The structures of L fractions (SH-1-L, SH-2-L and SH-3-L) were determined by nuclear magnetic resonance (NMR). SH-1-L was composed of two units, unit A (sulfated galactofucan) and unit B (sulfated xylo-glucuronomannan). Unit A contained a backbone of (1, 6-linked beta-D-Gal) n(1), (1, 3-linked 4-sulfated alpha-L-Fuc) n(2), (1, 3-linked 2, 4-di-sulfated alpha-L-Fuc) n(3), (1, 4-linked alpha-L-Fuc) n(4)and (1, 3-linked beta-D-Gal) n(5), accompanied by some branches, such as sulfated fuco-oligomers, sulfated galacto-oligomers or sulfated galacto-fuco-oligomers. And unit B consisted of alternating 1, 4-linked beta-D-glucuronic acid (GlcA) and 1, 2-linked alpha-D-mannose (Man) with the Man residues randomly sulfated at C6 or branched with xylose (Xyl) at C3. Both SH-2-L and SH-3-L were composed of unit A and their difference was attributed to the ratio of n(1): n(2): n(3): n(4): n(5). Based on monosaccharide analysis, we hypothesize that both SH-1-H and SH-2-H contained unit A and unit B while SH-3-H had a structure similar to SH-3-L. An assessment of anti-complement activities showed that the sulfated galactofucan had higher activities than sulfated galacto-fuco-xylo-glucuronomannan. These results suggest that the sulfated galactofucans might be a good candidate for anti-complement drugs.