Comparative study on the structures of intra- and extra-cellular polysaccharides from Penicillium oxalicum and their inhibitory effects on galectins

Here, we compare the content and composition of polysaccharides derived from the mycelium (40.4 kDa intracellular polysaccharide, IPS) and culture (27.2 kDa extracellular polysaccharide, EPS) of Penicillium oxalicum. Their chemical structures investigated by IR, NMR, enzymolysis and methylation analysis indicate that both IPS and EPS are galactomannans composed of α-1,2- mannopyranose (Manp) and α-1,6-Manp in a backbone ratio of ~3:1, respectively, both decorated with β-l,5-galactofuranose (Galf) side chains. A few β-l,6-Galf residues were also detected in the IPS fraction. EPS and IPS have different molecular weights (Mw) and degrees of branching. IPS obtained by alkaline extraction of P. oxalicum have been reported to be galactofuranans, a composition different from our IPS. Up to now, there have been no reports on the fine structure of EPS. Our results of galectin-mediated hemagglutination demonstrate that IPS exhibits greater inhibitory effects on five galectins compared with EPS. In addition, we find that Galf, a five-membered ring form of galactose, can also inhibit galectins. IPS may provide a new source of galectin inhibitors. These results increase our understanding of structure-activity relationships of polysaccharides as galectin inhibitors.