The structure of a polysaccharide isolated from Inonotus levis P. Karst. mushroom (Heterobasidiomycetes)

Inonotus levis biomass was extracted with 5% NaOH containing NaBH4, the insoluble material was discarded and the solution dialyzed. It was further treated with proteinase and the polymeric fraction isolated by gel chromatography. It contained mostly a polysaccharide of the following structure:β-GlcA-(1→2)-α-Gal-(1→6)-α-Gal3OMe-(1→[→6)-α-Gal-(1→6)-α-Gal3OMe-(1→]5–10where a non-reducing terminal glucuronic acid residue was present in about half of the molecules, making thus some of the chains acidic and others neutral. Methyl groups were present at about half of the galactose residues, however, no direct proof of the presence of defined repeating units was obtained due to NMR signals overlap. We believe that these short polymeric chains might be originally attached to a protein via serine or threonine residues and were cleaved off due to the alkaline conditions of extraction. Another polymer, co-extracted with this galactan, was a branched phosphorylated mannan with a structure similar to that of the mannan from Saccharomyces cerevisiae yeast.

Graphical abstractβ-GlcA-(1→2)-α-Gal-(1→6)-α-Gal3OMe-(1→[→6)-α-Gal-(1→6)-α-Gal3OMe-(1→]5–10