Structural properties of native and sonicated cinerean, a β-(1 → 3)(1 → 6)-d-glucan produced by Botrytis cinerea

Cinerean, the extracellular β-(1 → 3)(1 → 6)-d-glucan of the fungus Botrytis cinerea was studied. Electron micrographs of the native polysaccharide revealed quasi-endless fibrils with an estimated diameter of ca. 1.5 nm. A particle mass of 109–1010 daltons was determined from dilute solutions by low-angle laser light scattering. Sonication of increasing duration led to fragmentation of the native polymer with an approximately exponential decrease of mass in the range of average molecular masses between 250 000 and 50 000 daltons. Shadowed by platinum, cinerean fibril fragments with a weightaverage molecular mass of 172 000 ± 3000 daltons could be characterized from electron micrographs as a distribution of rods of most probable length of 45 nm and an average length of 72 nm. Smallangle X-ray scattering confirmed the fibrillar structure of the native cinerean and the rodlike structure of sonicated cinerean. A rod diameter of 1.9±0.2 nm and a mass per unit length of 2250±490 daltons/nm were found. The latter is in agreement with the value of 1830 daltons/nm calculated from the length distribution determined from the electron micrographs. These data — especially the mass per unit length — suggest a quaternary structure for the polysaccharide. Such a structure would explain the rigidity of the rods which, in turn, is responsible for the characteristic phase separation behaviour in aqueous solutions observed by nephelometry and viscometry.