Cell wall structure of mushroom sclerotium (Pleurotus tuber-regium): Part 2. Fine structure of a novel alkali-soluble hyper-branched cell wall polysaccharide

•We elucidate the hyper-branched structure of a novel alkali-soluble mushroom β-glucan by NMR.•We reveal the unfolded conformation of the hyper-branched β-glucan molecule by TEM and AFM.•We observe the multiple chains of the hyper-branched β-glucan molecule by AFM images.

The fine molecular structure of a novel alkali-soluble polysaccharide (SCA-I) from the mushroom sclerotial cell wall of Pleurotus tuber-regium was elucidated by 1-D and 2-D NMR spectroscopy as a hyper-branched glucan having a 64.9% degree of branching at O-6 and consisting a main chain with →1)-Glcp-(4→ linkages and short side chains having either →1)-Glcp-(3→ or →1)-Glcp-(6→ linkages. This partial structure of SCA-I was consistent with that obtained from methylation analysis. The molecular conformation of SDS-treated SCA-I was visualized for the first time by TEM and AFM. Microscopic images confirmed the highly branched structure of SCA-I as well as its multiple chain conformation when its compact structure was opened up by SDS treatment. This unique hyper-branched polysaccharide has the potential application in the design of carbohydrate-based nano-particles and drug delivery systems.

Graphical abstractPossible partial structure of the repeating unit of SCA-I.Figure optionsDownload full-size imageDownload as PowerPoint slide