Structural requirements of carbohydrates to bind Agaricus bisporus lectin

Gal beta 1-3GalNAc (T-disaccharide) and related molecules were assayed to d escribe the structural requirements of carbohydrates to bind Agaricus bispo rus lectin (ABL). Results provide insight into the most relevant regions of T-disaccharide involved in the binding of ABL. It was found that monosacch arides bind ABL weakly indicating a more extended carbohydrate-binding site as compared to those involved in the T-disaccharide specific lectins such as jacalin and peanut agglutinin, Lacto-N-biose (Gal beta 1-3GlcNAc) unlike T-disaccharide, is unable to inhibit the ABL interaction, thus showing the great importance of the position of the axial C-4 hydroxyl group of GalNAc in T-disaccharide, This finding could explain the inhibitory ability of Ga l beta 1-6GlcNAc and lactose because C-4 and C-3 hydroxyl groups of reducin g Glc, respectively, occupy a similar position as reported by conformationa l analysis. From the comparison of different glycolipids bearing terminal T -disaccharide bound to different linkages, it can be seen than ABL binding is even more impaired by an adjacent C-6 residual position than by the anom eric influence of T-disaccharide. Furthermore, the addition of beta-GlcNAc to the terminal T-disaccharide in C-3 position of Gal does not affect the A BL binding whereas if an anionic group such as glucuronic acid is added to C-3, the binding is partially affected. These findings demonstrate that ABL holds a particular binding nature different from that of other T-disacchar ide specific lectins.