Novel acidic β-glucans from Ganoderma lucidum: Structural characterization and molecular-weight-related antioxidant activity.

Ganoderma lucidum is a widely consumed edible-medicinal fungus and an important source of bioactive polysaccharides. However, how molecular weight and peripheral structural features relate to the antioxidant activity of its acidic β-glucans remains unclear. Here, three homologous acidic β-glucans, GLP-2a-2c, with molecular weights of 4.69-15.57 kDa, were isolated from G. lucidum fruiting bodies. HPGPC, monosaccharide profiling, UV/FT-IR spectroscopy, methylation-GC-MS, and 800 MHz 1D/2D NMR analyses identified multiple β-linked Glcp residue types, GlcA, and minor Fuc-, Ara-, and Man-related residues. In UV-irradiated HaCaT cells, the three fractions differed in antioxidant activity, and the intermediate-molecular-weight GLP-2b showed stronger effects on GSH-Px activity, MDA accumulation, and intracellular ROS than the other native fractions. GLP-2b (7.49 kDa) increased GSH-Px activity to approximately 2.1-fold of the UV control, lowered MDA content to about 35% of the UV control, and decreased intracellular ROS. The hydrolysate-derived fraction dGLP-2b (8.51 kDa) showed comparable ROS-reducing activity to GLP-2b despite differences in relative linkage composition. Within this molecular weight range, changes in linkage composition following mild hydrolysis were not associated with a detectable change in ROS-reducing activity. GLP-2b also attenuated UV-induced MAPK phosphorylation, with p38 showing the largest numerical reduction among the three MAPK readouts. These findings associate linkage characteristics of G. lucidum acidic β-glucan fractions with cellular antioxidant responses.