Polysaccharides from the edible mushroom Calocybe gambosa: structure and chain conformation of a (1→4),(1→6)-linked glucan

Three polysaccharides were isolated from the fruiting bodies of the mushroom Calocybe gambosa by cold water (PS-Cg fC), hot water (PS-Cg fH), and hot aqueous NaOH (PS-Cg fB) extractions. The size exclusion chromatograms presented in all cases a single peak showing a molecular weight of 145 kDa. On the basis of acid hydrolysis, methylation analysis, and NMR analysis, the structure of the three polysaccharides appeared to be equivalent. The three carbohydrates were composed of glucose and the methylation analysis showed that the units were (1 -> 4),(1 -> 6)-linked with a degree of branching (DB) of 4%. NMR experiments showed that the three fractions contained the same polysaccharide. H-1 NMR spectroscopy revealed that the linkages were beta-type in all cases. The complexation with Congo red demonstrated that the polysaccharides displayed a triple-strand helical conformation. The polysaccharides were composed of a repeating unit with a structure as below: ->[6)-beta-D-Glc-(1](21)->)-beta-D-Glc-(1 -> 6)-beta-D-Glc-(1 -> 4 up arrow 1 [beta-D-Glc](2) (C) 2013 Elsevier Ltd. All rights reserved.