Structural characterization of an immunoenhancing glucan isolated from a mushroom Macrolepiota dolichaula

•A soluble branched β-d-glucan (PS-I) was isolated from the mushroom M. dolichaula.•Structure of the PS-I was determined by chemical as well as 1D/2D NMR studies.•The PS-I showed in vitro macrophage activation.•It also showed splenocyte and thymocyte activation in mouse cell culture medium. A water soluble branched glucan (PS-I) was isolated from aqueous extract of the fruit bodies of an edible mushroom Macrolepiota dolichaula, having average molecular weight ∼2.02×105Da. The structure of this PS-I was determined using total hydrolysis, methylation analysis, Smith degradation, partial hydrolysis, and 1D/2D NMR experiments. Total hydrolysis and methylation analysis results showed the presence of (1→3, 6)-, (1→6)-, (1→4)-, (1→3)-linked and terminal β-d-glucopyranosyl residues in a relative proportion of nearly 1:2:1:1:1. All the chemical and NMR results indicated that the PS-I was a branched glucan, and the repeating unit of this glucan consisted of a backbone chain of three (1→6)-linked-β-d-glucopyranosyl residues where one of the backbone residues is branched at O-3 with (1→3)- moiety which is further attached to another (1→4)- residue and terminated with a non-reducing β-d-glucopyranosyl residue. The PS-I exhibited in vitro macrophage activation in RAW 264.7 cell line as well as splenocyte and thymocyte activation in mouse cell culture medium.