Structural differences and conformational characterization of five bioactive polysaccharides from Lentinus edodes

Five polysaccharide fractions (LST1, LST2, LJT1, LJT2 and LJT3) from Lentinus edodes were isolated and purified. Their molecular weights (Mw) were estimated as 65.5 ~ 697 kDa by using high-performance gel permeation chromatography (HPGPC). The results from monosaccharide analysis indicated that all of them contained glucose as main sugar component. The chemical and spectroscopic analyses implied that these fractions were composed of a main chain consisting of several (2 ~ 6) β-(1 → 3)-d-glucose residues with branching at C6 position. The predicted structural units of the purified polysaccharides were established with different degrees of branching (DB). Congo-red test, X-ray diffraction (XRD) and atomic force microscope (AFM) were used to verify that the natural lentinan contained triple helical spatial conformation. Furthermore, the results from anti-tumor tests in vitro and in vivo revealed that these polysaccharide fractions could have dual anti-tumor effects, including killing tumor cells directly and immunoregulation with low toxicity to the host. Interestingly, the high Mw polysaccharides had smaller DB values and displayed greater anti-tumor effects.