Effect of polyvalencies of glycotopes on the binding of a lectin from the edible mushroom, Agaricus bisporus

Agaricus bisporus agglutinin (ABA) isolated from edible mushroom has a potent anti-proliferative effect on malignant colon cells with considerable therapeutic potential as an anti-neoplastic agent. Since previous studies on the structural requirement for binding were limited to molecular or submolecular levels of Galβ1-3GalNAc (T; Thomsen-Friedenreich disaccharide glycotope; where Gal represents D-galactopyranose and GalNAc represents 2-acetamido-2-deoxy-D-galactopyranose) and its derivatives, the binding properties of ABA were further investigated using our collection of glycans by enzyme-linked lectinosorbent assay and lectin-glycan inhibition assay. The results indicate that polyvalent Galβ1-related glycotopes, GalNAcα1-Ser/Thr (Tn), and their cryptoforms, are the most potent factor for ABA binding. They were up to 5.5 × 10⁵ and 4.7 × 10⁶ times more active than monomeric T and GalNAc respectively. The affinity of ABA for ligands can be ranked as: multivalent T_α (Galβ1-3GalNAcα1-), Tn and I/II (Galβ1-3GlcNac/Galβ1-4GlcNAc, where GlcNAc represents 2-acetamido-2-deoxy-D-glucopyranose) 〉 〉 〉 〉 monomeric T_α and Tn 〉 I 〉 〉 GalNAc 〉 〉 〉 II, L (Galβ1-4Glc, where Glc represents D-glucopyranose) and Gal (inactive). These specific binding features of ABA establish the importance of affinity enhancement by high-density polyvalent (versus multiantennary I/II) glycotopes and facilitate our understanding of the lectin receptor recognition events relevant to its biological activities.