Structural characterization and immunomodulatory activity of a novel polysaccharide from Pteridium aquilinum

PAP1-A, a novel heteropolysaccharide with an average molecular mass of 1.35 × 105 Da, was isolated from Pteridium aquilinum using a combination of chromatography by DEAE Sepharose Fast Flow and Sepharose 4B. The monosaccharide component of PAP1-A was L-rhamnose, L-arabinose, L-fucose, D-xylose, D-mannose, D-glucose and D-galactose in the molar ration of 1.82: 1.53: 1.42: 1.31: 5.24: 1: 12.35. The predicted structure of PAP1-A was established to be a complex polysaccharide with a main chain consisted of α-(1 → 4)-linked galactose partially substituted at O-6 position, with the (1 → 2)-linked xylose, (1 → 3)-linked arabinose, (1 → 3)-linked rhamnose, (1 → 3,6)-linked mannose, and (1 → 6)-linked mannose, as branches. Fucose, glucose, mannose, and rhamnose were located at the termini of the branches. The immunomodulatory activity assay showed that PAP1-A could significantly promote the RAW264.7 cells proliferation and induce the production of NO from RAW264.7 cells. Therefore, PAP1-A shows as a potent immunomodulator with potential applications in the medical and food industries.