The Galβ-(syn)-gauche configuration is required for galectin-recognition disaccharides

Galectins form a large family of animal lectins, individual members having variously divergent carbohydrate-recognition domains (CRDs) responsible for extensive physiological phenomena. Sugar-binding affinities of galectins were previously investigated by us using frontal affinity chromatography (FAC) with a relatively small set (i.e., 41) of oligosaccharides. However, total understanding of a consensus rule for galectin-recognition saccharides is still hampered by the lack of fundamental knowledge about their sugar-binding specificity toward a much larger panel of oligosaccharides in terms of dissociation constant (K(d)).

In the present study, we extended a FAC analysis from a more systematic viewpoint by using 142 fluorescent-labeled oligosaccharides, initially with focus on functional human galectins-1-9. Binding characteristics were further validated with 11 non-human galectins and 13 non-galectin Gal/GalNAc-binding lectins belonging to different families.

An empirical [Galβ-equatorial] rule for galectin-recognition disaccharides was first derived by our present research and previous works by others. However, this rule was not valid for a recently reported nematode disaccharide, "Galβ1-4-L-Fuc" [Butschi et al. PLoS Pathog, 2010; 6(1):e1000717], because this glycosidic linkage was directed to 'axial' 4-OH of L-Fuc. After careful reconsideration of the structural data, we reached an ultimate rule of galectin-recognition disaccharides, which all of the galectins so far identified fulfilled, i.e., under the re-defined configuration "Galβ-(syn)-gauche". The rule also worked perfectly for differentiation of galectins from other types of lectins.

The present attempt should provide a basis to solve the riddle of the glyco-code as well as to develop therapeutic inhibitors mimicking galectin ligands.