The molecular structure and solution conformation of an acidic heteropolysaccharide from Auricularia auricula-judae

A water soluble acidic heteropolysaccharide named WAF was isolated from Auricularia auricula‐judae by extracting with 0.9% NaCl solution. By using gas chromatography, gas chromatography‐mass spectrometry, and NMR, its chemical structure was determined to be composed of a backbone of α‐(1→3)‐linked D‐mannopyranose residues with pendant side groups of β‐D‐xylose, β‐D‐glucose, or β‐D‐glucuronic acid at position O6 or O2. Six fractions prepared from WAF with a weight‐average molecular mass (Mw) between 5.9 × 104 and 64.7 × 104 g/mol were characterized with laser light scattering and viscometry in 0.1M NaCl at 25°C. The dependence of intrinsic viscosity ([η]) and radius of gyration (Rg) on Mw for this polysaccharide were found to be [η] = 1.79 × 10−3Mw0.96 cm3 g−1 and Rg = 6.99 × 10−2 Mw0.54 nm. The molar mass per unit contour length (ML) and the persistence length (Lp) were estimated to be 1124 nm−1 and 11 nm, respectively. The WAF exhibited a semirigid character typical of linear polysaccharides. Molecular modeling was then used to predict the ordered and disordered states of WAF; the simulated ML and Lp were however much smaller than the experimental values. Taken altogether, the results suggested that WAF formed a duplex in solution. © 2010 Wiley Periodicals, Inc. Biopolymers 95: 217–227, 2011.