Structure and chain conformation of a neutral polysaccharide from sclerotia of Polyporus umbellatus

A water-soluble heteropolysaccharide (PUP60W-1) was purified from the hot water extract of sclerotia of P. umbellatus by chromatography with DEAE Sepharose Fast Flow and Sephacryl S200 High-Resolution. The primary structure of PUP60W-1 was elucidated by GC, GC-MS and NMR. PUP60W-1 was identified as a highly branched polysaccharide composed of fucose, glucose and galactose in a ratio of 1.0:0.9:13.3. The main repeating unit was identified as α-(1→6)-d-galactopyranan backbone with substitution of terminal α-galactopyranosyl residues at O-2 for two out of every three main chain galactose residues. Its chain conformation was studied by atom force microscopy and size exclusion chromatography coupled with multiple detectors. The results revealed that PUP60W-1 had a molecular weight of 2.47×10⁴Da with a polydispersity index of 1.04, and existed in water as compact sphere structures which could be disrupted into smaller spherical chain blocks after dispersion with sodium dodecyl sulfate.