A structure of the complex between concanavalin A and methyl-3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside reveals two binding modes

The structure of concanavalin A in complex with the trimannoside methyl-3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside has been determined in a novel space group. In three of the four subunits of the concanavalin A tetramer, the interactions between the protein and the bound saccharide are essentially identical to those reported previously by other authors (Naismith, J. H., and Field, R. A. (1996) J. Biol. Chem. 271, 972-976). In the fourth subunit, however, the alpha1-->3 linkage has a different conformation, resulting in a different part of the alpha1-->3-linked mannose interacting with essentially the same surface of the protein. Furthermore, significant differences are observed in the quaternary associations of the subunits compared with the saccharide-free structures and other carbohydrate complexes, suggesting that the concanavalin A tetramer is a rather flexible entity.