Structural basis for the unusual carbohydrate-binding specificity of jacalin towards galactose and mannose

Abstract

Evidence is presented that the specificity of jacalin, the seed lectin from jack fruit (Artocarpus integrifolia), is not directed exclusively against the T-antigen disaccharide Galβ1,3GalNAc, lactose and galactose, but also against mannose and oligomannosides. Biochemical analyses based on surface-plasmon-resonance measurements, combined with the X-ray-crystallographic determination of the structure of a jacalin—α-methyl-mannose complex at 2Å resolution, demonstrated clearly that jacalin is fully capable of binding mannose. Besides mannose, jacalin also interacts readily with glucose, N-acetylneuraminic acid and N-acetylmuramic acid. Structural analyses demonstrated that the relatively large size of the carbohydrate-binding site enables jacalin to accommodate monosaccharides with different hydroxyl conformations and provided unambiguous evidence that the β-prism structure of jacalin is a sufficiently flexible structural scaffold to confer different carbohydrate-binding specificities to a single lectin.