Isolation and characterization of a hyperbranched proteoglycan from Ganoderma Lucidum for anti-diabetes

•A noval proteoglycan, named FYGL-n, was extracted from G. lucidum.•FYGL-n was an efficient PTP1B inhibitor with IC50 7.8±0.2μg/mL.•The polysaccharide moiety of FYGL-n was composed of Ara, Gal, Rha and Glc.•The molecular weight of the FYGL-n was 72.9kDa.•The complete sequence of FYGL-n was established indicating a hyperbranched biopolymer. Presently, an efficient protein tyrosine phosphatase 1B (PTP1B) inhibitor, named FYGL-n, was isolated from Ganoderma Lucidum and characterized for its structure and bioactivity. Structure and chain conformation of FYGL-n based on both chemical and spectroscopic analysis showed that FYGL-n was a hyperbranched heteropolysaccharide bonded with protein via both serine and threonine residues by O-type glycoside, and showed a sphere observed by AFM. Specifically, monosaccharide composition indicated that FYGL-n consisted of d-arabinose, d-galactose, l-rhamnose and d-glucose in a mole ratio of 0.08:0.21:0.24:0.47, with a molecular mass of 72.9kDa. The analysis of amino acids in FYGL-n indicated that there were 16 common amino acids, among which aspartic acid, glycine, serine, alanine, glutamic acid and threonine were the dominant components. Also it was demonstrated that FYGL-n could inhibit the PTP1B activity on a competitive mechanism in vitro.