Structural elucidation of an immunoenhancing heteroglycan isolated from Russula albonigra (Krombh.) Fr.

A water soluble heteroglycan (PS-II) of average molecular weight ∼1.45 × 105 Da was isolated from the aqueous extract of an ectomycorrhizal edible mushroom, Russula albonigra (Krombh.) Fr. Structural characterization of PS-II was carried out using acid hydrolysis, methylation analysis, periodate oxidation, and 1D/2D NMR studies. Structural analysis revealed that PS-II was composed of terminal 2-O-methyl-Fucp, terminal Manp, (1→2)-Fucp, (1→3)-Glcp, (1→3,4)-Glcp, (1→6)-Galp, and (1→2,6)-Galp residues in a relative proportion of approximately 1:1:1:1:1:1:1. The proposed repeating unit of the PS-II had a backbone consisting of two (1→3)-β-d-glucopyranosyl, two (1→6)-α-d-galactopyranosyl, and one (1→2)-α-l-fucopyranosyl residues, out of which one (1→3)-β-d-glucopyranosyl residue was branched at O-4 position with terminal 2-O-methyl-α-l-fucopyranosyl and one (1→6)-α-d-galactopyranosyl residue was branched at O-2 position with terminal α-d-mannopyranosyl residue. This PS-II showed in vitro macrophage activation by NO production as well as splenocytes and thymocytes proliferation.