MUTATIONAL ANALYSIS OF CARBOHYDRATE BINDING SITES IN AGARICUS BISPORUS LECTIN

ISSOGLIO, FEDERICO M.; IRAZOQUI, FERNANDO J.; CURTINO, JUAN A.; CARRIZO MARÍA E.

Rosario, Santa Fé, Argentina.

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2006

ABL, the lectin from the common edible mushroom Agaricus bisporus, has potent antiproliferative effects on human epithelial cancer cells without any apparent cytotoxicity. The three-dimensional structure of the lectin has been recently determined by X-ray crystallography (Carrizo, M.E. et al., J. Biol. Chem., 280, 10614-23, 2005). ABL is a tetramer and each monomer presents a novel fold with two b sheets connected by a helix-loop-helix motif. These studies showed that Galb1-3GalNAc, the disaccharide moiety of Thomsen Friedenreich antigen (TFD), binds at a depression on the surface of the molecule, while GlcNAc binds at a different site on the opposite side of the helix-loop-helix motif. Among the contacts involved in providing the specificity of each binding site are the interactions between the side chain of Asn-73 and the acetamido group of GalNAc and Asp-79 with O4 and O6 of GlcNAc. Site-directed mutational changes were introduced at these residues with the objective of probing their role. The mutants N73E and N73Q show similar binding affinity for TFD, while N73A is less potent for the recognition of the disaccharide. On the other hand, the mutant D79A  has a very low affinity for GlcNAc. Preliminary studies indicate that this mutant has an inhibitory effect on HT29 cell proliferation higher than the produced by ABL wt.