Structural elucidation of a heteroglycan from the fruiting bodies of Agaricus blazei Murill

One water-soluble polysaccharide (ABP-W1) was purified from the fruiting bodies of Agaricus blazei by DEAE Sepharose Fast Flow and Sepharose 6 Fast Flow column chromatography. Its molecular weight was about 3.9 × 102 kDa as determined by high-performance size-exclusion chromatography (HPSEC). The structural feature of ABP-W1 was investigated by a combination of chemical and instrumental analysis, including partial hydrolysis with acid, periodate oxidation-Smith degradation, acetylation, methylation analysis and nuclear magnetic resonance spectroscopy (NMR 1H, 13C). The results revealed that ABP-W1 had a backbone consisting of (1 → 6)-linked-α-d-galactopyranosyl and (1 → 2,6)-linked-α-d-glucopyranosyl, which was branched with one single terminal (1→)-α-d-glucopyranosyl at the O-2 position of (1 → 2,6)-linked-α-d-glucopyranosyl along the main chain in the ratio of 1:1:1. The observation of the complex-formation between ABP-W1 and Congo Red indicated that ABP-W1 probably existed in a triple-strand helical conformation in water. Based on the data obtained, ABP-W1 was composed of a repeating unit with a structure as below: