FIP-fve is a protein that is isolated from Flammulina velutipes . Its known immunomodulatory activities are elicitation of the production of type II interferon from human peripheral mononuclear cells (hPBMCs) and hemagglutination. How the target receptors mediate activation of FIP-fve-induced immunomodulatory effects remains to be elucidated. This study postulates the three-dimensional structures to determine whether the carbohydrate binding module family 34 (CBM-34) on FIP-fve is conserved to site N of Thermoactinomyces vulgaris R-47 α-amylase I. Experimental site-directed mutagenesis data as well as ligand-specific binding competition assay are adopted to identify the key residues W24, T28, D34, T90, I91, and W111 of FIP-fve that participate in binding to polysaccharides that are linked to the membrane of immune cells. Treatments of hPBMCs with tunicamycin and deglycosylation enzymes that removed the carbohydrate moieties reduced the secretion of IFN-γ induction from hPBMCs. In conclusion, the experiments herein demonstrated the ligand-binding CBM-34 on FIP-fve and ligand-like glycoproteins on the surface of hPBMCs must be required to induce physiological immunomodulatory effects.
