Structural characterization and bioactivity evaluation of an acidic proteoglycan extract from Ganoderma lucidum fruiting bodies for PTP1B inhibition and anti-diabetes

A water-soluble PTP1B inhibitor, named FYGL-a, was fractionated for structure investigation and bioactivity evaluation. FYGL-a is an ingredient of a reported antihyperglycemia extract from Ganoderma Lucidum fruiting bodies. Composition analysis indicated that FYGL-a was a 100.2 kDa acidic proteoglycan, consisting of 85 ± 2% heteropolysaccharide chain with rhamnose, galactose, glucose, and glucuronic acid residues in a mole ratio of 1.0:3.7:3.9:2.0, and the 15 ± 2% protein moiety of FYGL-a was covalently bonded to the polysaccharide chain in O-linkage type via threonine residues. The complete sequence of FYGL-a was characterized systematically by periodate oxidation, Smith degradation, methylation analysis, ¹H & ¹³C 1D NMR, and 2D NMR (HSQC, HMBC, NOESY, COSY, & TOCSY). The chemical structure of FYGL-a was determined as following, which may play special role in the competitive inhibition of PTP1B and antihyperglycemia potency.