The isolation, characterization, cloning and expression of the lectin (agglutinin) from Marasmius oreades (MOA) is described. MOA displays unique carbohydrate binding properties, including blood group B-specific agglutination and preferential binding to Ga11,3Ga1-containing sugar epitopes, including but not limited to Ga11,3Ga11,4G1cNAc. MOA is contemplated as an affinity reagent, a therapeutic in the treatment of antibiotic-induced diarrhea and the field of xenotransplantation. MOA may also serve as a diagnostic reagent, e.g. for malaria.