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 alpha-(1 -> 3)-linked D-mannopyranose residues with pendant side groups of beta-D-xylose, beta-D-glucose, or beta-D-glucuronic acid at position O6 or O2. Six fractions prepared from WAF with a weight-average molecular mass (M-w) between 5.9 X 10(4) and 64.7 X 10(4) g/mol were characterized with laser light scattering and viscometry in 0.1M NaCl at 25 degrees C. The dependence of intrinsic viscosity ([eta]) and radius of gyration (R-g) on M-w for this polysaccharide were found to be [eta] = 1.79 X 10(-3) M-w(0.96) cm(3) g(-1) and R-g = 6.99 X 10(-2) M-w(0.54) nm. The molar mass per unit contour length (M-L) and the persistence length (L-p) 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 M-L and L-p were however much smaller than the experimental values. Taken altogether, the results suggested that WAF formed a duplex in solution. (C) 2010 Wiley Periodicals, Inc. Biopolymers 95: 217-227, 2011.