Mannose in Complex with Colocasia esculenta Tuber Agglutinin

The major tuber storage protein of Colocasia esculenta is a monocot mannose-binding, widely used, dietarylectin, for which a crystal structure was previously shown to consist of four β-prism II domains or two αβheterodimers, each forming a α2β2 heterotetramer with a symmetry related unit. In the present study, the same lectincrystallized in the presence of a 50 molar excess of free mannose, persists in forming such α2β2 heterotetramers.Lectin crystals apparently complexed to mannose were obtained by hanging-drop, vapor-diffusion method at roomtemperature and high-resolution X-ray diffraction data were collected using a home X-ray source. Using the crystalstructure of the Remusatia vivipara lectin, the structure of the complex has been solved by molecular replacementand subsequent crystallographic refinement. Five different mannose binding sites per heterodimer with partialoccupancy have been found, among which only one appears to bind close to a classical carbohydrate recognitionsite characterized earlier for these lectins. Mannose binding at these five sites is described.