Structural requirements of carbohydrates to bind Agaricus bisporus lectin

Galbeta1-3GalNAc (T-disaccharide) and related molecules were assayed todescribe the structural requirements of carbohydrates to bind Agaricusbisporus lectin (ABL). Results provide insight into the most relevantregions of T-disaccharide involved in the binding of ABL. It was found thatmonosaccharides bind ABL weakly indicating a more extendedcarbohydrate-binding site as compared to those involvedin the T-disaccharide specific lectins such as jacalin and peanut agglutinin.Lacto-N-biose (Galbeta1-3GlcNAc) unlike T-disaccharide, is unable toinhibit the ABL interaction, thus showing the great importance of theposition of the axial C-4 hydroxyl group of GalNAc in T-disaccharide. Thisfinding could explain the inhibitory ability of Galbeta1-6GlcNAc andlactose because C-4 and C-3 hydroxyl groups of reducing Glc, respectively,occupy a similar position as reported by conformational analysis. From thecomparison of different glycolipids bearing terminal T-disaccharide boundto different linkages, it can be seen than ABL binding is even moreimpaired by an adjacent C-6 residual position than by the anomericinfluence of T-disaccharide. Furthermore, the addition of beta-GlcNAc tothe terminal T-disaccharide in C-3 position of Gal does not affect the ABLbinding whereas if an anionic group such as glucuronic acid is added toC-3, the binding is partially affected. These findings demonstrate that ABLholds a particular binding nature different from that of otherT-disaccharide specific lectins.