Fractionation and characterization of a protein–polysaccharide complex fromPleurotus tuberregium sclerotia

Abstract

A water-soluble sample (TM4b), extracted from sclerotia of Pleurotus tuberregium, was analyzed using elemental analysis, one- and two-dimensional 1 H and 1 3 C NMR. The results indicated that TM4b was protein-polysaccharide complex, and the polysaccharide moiety was hyperbranched β-D-glucan with residuals branched at C3, C2, C4, and C6 positions. A preparative size-exclusion chromatography (SEC) column combined with nonsolvent addition method was used to fractionate TM4b, and nine fractions were obtained. Solution properties of TM4b in 0.15 M aqueous NaCl were studied using static laser light scattering and viscometry at 25°C. The dependences of intrinsic viscosity ([η]) and radius of gyration ( z 1/2 ) on weight-average molecular weight (M w ) for TM4b in the M w range from 1.89 X 10 4 to 2.58 X 10 6 were found to be [η] = 0.21Mw 0.32±0.4 and z 1/2 = 3.63M w 0.21±0.02 . It indicated that TM4b existed as compact sphere conformation in the aqueous solution. Atomic force microscopy image further confirmed that the TM4b molecules exhibited globular shape in the solution. This work gave valuable information on fractionation and chain conformation characterization of the globular protein-polysaccharide complex.