Renaturation of triple helical polysaccharide lentinan in water-diluted dimethylsulfoxide solution.

Triple helical lentinan, a beta-(1-->3)-D-glucan from Lentinus edodes, was denatured in dimethylsulfoxide (DMSO) into single random coils. The randomly coiled lentinan/DMSO solutions were diluted with pure water to w(H) (the weight fraction of water in the mixed solvent) of 95%, and their intrinsic viscosity [eta], weight-average molecular weight M(w), radius of gyration R(g), and hydrodynamic radius R(h) were investigated at 25 degrees C after over 5-day storage. The [eta] and M(w) values, especially the conformation parameter rho (identical with R(g)/R(h)), of the renatured lentinan were close to those of the originally extracted one, suggesting that random lentinan chains in DMSO were reassembled into triple helical structures. Moreover, the renatured lentinan in 95% water/5% DMSO solution exhibited a unique behavior of triple helical glucans that shear modulus G' decreased sharply at temperature from 8.4 degrees C to 13.3 degrees C with increasing temperature, which was ascribed to the intramolecular conformation transition from ordered triple helical I to disordered triple helical II. The AFM images gave was suggested intuitively evidence that the renatured lentinan mainly existed as rod-like chains, supporting that formation of triple helical structure. The optimal lentinan concentration for triple helical configuration formation was estimated to be over 0.04%. The time dependence of R(h) and UV absorption of the water-diluted lentinan/DMSO solution with an indicator of azo dye of Congo red suggested that renaturation of triple helix was a very rapid process. Moreover, the blue-shift of UV-vis absorption spectra suggested that the dye molecules of Congo red were assembled into supramolecular structure in the hydrophobic cavity of the renatured triple helical lentinan. All the results showed that the triple helical structure formed once the randomly coiled lentinan/DMSO was diluted to the final water content of 95%.