Purification, structural elucidation and immunostimulatory effect of a new protein-polysaccharide conjugate produced by Nervilia fordii

A novel protein-polysaccharide conjugate NFP-A4 was isolated and purified from water extracts of Nervilia fordii. The polysaccharide chain of NFP-A4 was found to contain D-galacturonic acid, D-galactose, D-glucose, L-arabinose, D-glucuronic acid, L-rhamnose, and D-mannose. The protein content of NFP-A4 was determined to be 12.83%, and it was bound to the polysaccharide chain via O-linkages at the serine and threonine residues. NFP-A4 was found to significantly activate macrophages and also induce immunomodulatory responses. These data suggest that NFP-A4 is a major bioactive component of N. fordii and may be responsible for many of its therapeutic properties.