Polymorphism of curdlan and (1 → 3)-β-d-glucans synthesized in vitro: A 13C CP-MAS and X-ray diffraction analysis

The polymorphism of three different forms of curdlan and four (1 → 3)-β-d-glucans synthesized in vitro was investigated by 13C cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR) spectroscopy and X-ray powder diffraction. Dried samples of curdlan presented a disordered state whereas two distinct hydrated crystalline structures were evidenced for the polymer after hydrothermal treatment or swelling in water at room temperature. The samples synthesized in vitro by detergent extracts of plasma membranes from Rubus fruticosus and Saprolegnia monoica and by a mutated barley (1 → 3)-β-d-glucan endohydrolase exhibited a structural heterogeneity that can be explained in the light of the results obtained on standard samples. A 76-ppm resonance signal corresponding to carbon five was identified by CP/MAS NMR spectroscopy. The relative importance of this peak was shown to be linked to the proportion of the different crystalline allomorphs in a given sample. This peak can be considered as a new marker of the degree of organization of (1 → 3)-β-d-glucans. The observed polymorphism provides further detailed information on the conformation of the different (1 → 3)-β-d-glucan allomorphs.