Structural elucidation of a branch-on-branch β-glucan from Hericium erinaceus with A HPAEC-PAD-MS system.

• A 1−6 glucanase was firstly used to digest a β-glucan from H. erinaceus. • The oligosaccharides in the digested products were analyzed with HPAEC-MS. • The sequences of enzyme resistant oligosaccharides were elucidated with MS/MS. • A branch-on-branch structure of the β-glucan was estimated. A water-soluble β-glucan from fruiting body of Hericium erinaceus was obtained after water extraction, purification and fractionation. Analyses of monosaccharide composition, molecular weight and linkage mode demonstrated that it is a β-glucan with 1→3 and 1→6 linkage modes and a molecular weight of 13.3 kDa. An endo-1,6-β- d -glucanase was used to digest the β-glucan and the digested products over time were analyzed with a HPAEC-PAD-MS platform. The linkage mode of each glycosidic bond in the digested oligosaccharides were confirmed with MS/MS. At the end of digestion, enzyme resistant oligosaccharides were observed as several 1→6 linked glucoses with one or two 1→3 linked glucose residues. All these domains are more like constructional pieces from a branch-on-branch glucan, in which multiple 1→6 linked glucan chains are hooked through one or two 1→3 linked glucose residues. Averagely, there is a 1→3 linkage per six 1→6 linked glucoses in this branch-on-branch β-glucan. [ABSTRACT FROM AUTHOR]