Screening of mushrooms from the woodlands of Zimbabwe: Occurrence of lectins and partial purification of a mucin specific lectin from Boletus edulis

Mushrooms are known to possess a diversity of bioactive compounds that include lectins, which are proteins or glycoproteins that bind specifically to cell surface carbohydrates, culminating in cell agglutination. The present study describes the screening of lectin activity from ten local mushrooms, namely, Amanita zambiana, Boletus edulis, Cantharellus heinemannianus, Cantharellus miomboensis, Cantharellus symoensii, Lactarius kabansus, Amanita sp., Coprinus sp., Ganoderma lucidum and Trametes strumosa. The lectin content was detected by the haemagglutination activity of mushrooms against sheep and goat erythrocytes. Among the different mushrooms screened Amanita sp., Boletus edulis and Lactarius kabansus showed high lectin activity (39, 617 and 77 HAU/mg mushroom, respectively). Boletus edulis was used for the haemagglutination inhibition assay. A total of twenty sugars and sugar derivatives, namely, alpha-lactose, D-glucose, D-mannose, D-raffinose, N-acetyl glucosamine, maltose, melibiose, D-ribose, porcine mucin, D-cellobiose, D-arabinose, alpha-methyl-D-glucoside, methyl-alpha-D-mannopyranoside, D-trehalose, L-arabinose, L-sorbose, L-lyxose, beta-lactose, DL-xylose, and D-galactose, were used for the haemagglutination inhibition assay. Of the various carbohydrates tested, only porcine mucin was found to be the most potent inhibitor of Boletus lectin. The lectin from Boletus mushroom was partially purified using ammonium sulphate precipitation. The highest lectin activity was observed in the 30%-60% fraction. This study revealed for the first time the occurrence of lectins in the local Zimbabwean mushrooms studied as well as isolation of a novel mucin-specific lectin. The information obtained can be used for further investigation of cell surface sugars, purification and characterisation of glycoproteins and their contribution towards the medicinal properties of local mushrooms.