The 1.2 angstrom resolution structure of the Con A-dimannose complex

The complex between concanavalin A (Con A) and alpha1-2 mannobiose (mannose alpha1-2 mannose) has been refined to 1.2 Angstrom resolution. This is the highest resolution structure reported for any sugar-lectin complex. As the native structure of Con A to 0.94 Angstrom resolution is already in the da tabase, this gives us a unique opportunity to examine sugar-protein binding at high resolution. These data have allowed us to model a number of hydrog en atoms involved in the binding of the sugar to Con A, using the differenc e density map to place the hydrogen atoms. This map reveals the presence of the protonated form of Asp208 involved in binding. Asp208 is not protonate d in the 0.94 Angstrom native structure. Our results clearly show that this residue is protonated and hydrogen bonds to the sugar. The structure accou nts for the higher affinity of the alpha1-2 linked sugar when compared to o ther disaccharides. This structure identifies different interactions to tho se predicted by previous modelling studies. We believe that the additional data presented here will enable significant improvements to be made to the sugar-protein modelling algorithms. (C) 2001 Academic Press.