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 (M(w)) 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 (R(g)) on M(w) for this polysaccharide were found to be [η] = 1.79 × 10⁻³ M(w) ⁰.⁹⁶ cm³ g⁻¹ and R(g) = 6.99 × 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.