Structural characterization and antiviral activity of a novel heteropolysaccharide isolated from Grifola frondosa against enterovirus 71

A novel heteropolysaccharide from Grifola frondosa mycelia was extracted and purified using DEAE Sephadex A-50 and Sephadex G-200 chromatography. Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (1H NMR and 13C NMR) spectroscopy were used to decipher the structure of the purified G. frondosa polysaccharide (GFP1). Chemical and spectral analysis revealed that GFP1, with an average molecular weight of 40.5 kDa, possessed a 1,6-β-d-glucan backbone with a single 1,3-α-d-fucopyranosyl side-branching unit. Enterovirus 71 (EV71) is the causative pathogen of hand-foot-and-mouth disease. GFP1 was tested for its anti-EV71 activity in cultured cells, which showed that EV71 viral replication was blocked and viral VP1 protein expression and genomic RNA synthesis were suppressed. Moreover, GFP1 exhibited apoptotic and other activities by suppressing the EV71-induced caspase-3 cleavage and IκBα down regulation. Our results demonstrate that the novel G. frondosa polysaccharide has antiviral activity, which could be valuable as a potentially new anti-EV71 therapeutic compound.