One of these loops contains transition metals, calcium and manganese, which keep the amino acid residues of the sugar-binding site at the required positions. Amino acid sequences of this loop play an important role in the carbohydrate-binding specificities of these lectins. The most likely function for the plant lectins is plant defense. Legume lectins, especially are also involved in the recognition of bacteria for the purpose of establishing symbiosis. Yellow, red and blue part shows a beta sheet, an alpha helix and a loop, respectively.
Legume lectins- a large family of homologous proteins.