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

A water soluble heteroglycan (PS-II) of average molecular weight similar to 1.45 x 10(5) 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 (13)-beta-D-glucopyranosyl, two (1 -> 6)-alpha-D-galactopyranosyl, and one (1 -> 2)-alpha-L-fucopyranosyl residues, out of which one (1 -> 3)-beta-D-glucopyranosyl residue was branched at O-4 position with terminal 2-O-methyl-alpha-L-fucopyranosyl and one (1 -> 6)-alpha-D-galactopyranosyl residue was branched at O-2 position with terminal alpha-D-mannopyranosyl residue. This PS-II showed in vitro macrophage activation by NO production as well as splenocytes and thymocytes proliferation. (C) 2013 Elsevier Ltd. All rights reserved.