A glucomannogalactan from Pleurotus geesteranus: Structural characterization, chain conformation and immunological effect

A water-soluble glucomannogalactan was isolated from P. geesteranus fruit bodies by hot water extraction and column chromatography method. The structure, chain conformation and immune effect of PGP-1c (20.9 kDa) were investigated comprehensively based on high purity and neutral sugar content (94.7 ± 0.5%). Confirmed by monosaccharide composition, methylation and NMR analysis, PGP-1c was composed of unsubstituted (1,6-α-Gal and 1,6-α-3-OMe-Gal) and monosubstituted (1,2,6-α-Gal and 1,2,6-α-3-OMe-Gal) galactose units in the backbone through α-(1 → 6) glycosidic bonds and the possible branches that a long-branched chain composed of →3)-Glc-(1 → Man and a few fucoses were connected at the O-2 of galactose with a branching degree of 48%. Through the conformational behavior of the molecular chain, it was observed that PGP-1c might have a long-branched or stacked macromolecular network caused by O-CH3 groups. Moreover, PGP-1c could promote the secretion of NO and cytokines significantly in a dose-dependent manner, which indicated a good immune-enhancing effect.