Structural characterisation and immunomodulatory property of an acidic polysaccharide from mycelial culture of Cordyceps sinensis fungus Cs-HK1

An acidic polysaccharide, designated AEPS-1, was fractionated from the exopolysaccharide (EPS) produced by a medicinal fungus Cordyceps sinensis Cs-HK1 in mycelial culture. The molecular structure of AEPS-1 was characterised and elucidated by spectral and chromatographic analyses, and through derivatization by periodate oxidation, Smith degradation and methylation. AEPS-1 was composed of glucopyranose (Glcp) and pyrano-glucuronic acid (GlcUp) in an 8:1 M ratio plus a trace amount of mannose, having an average molecular weight of about 36 kDa. AEPS-1 had a linear backbone of (1→3)-linked α-d-Glcp residues with two branches, α-d-Glcp and α-d-GlcUp, attached to the main chain by (1→6) glycosidic bonds at every seventh α-d-Glcp unit. Atomic force microscopy revealed that AEPS-1 formed large networks in water that are connected primarily with triple helical strands. In Raw264.7 macrophage cell cultures, AEPS-1, at suitable doses between 25 and 250 μg/ml, significantly stimulated the release of several major cytokines, demonstrating an immunomodulatory property.