Indole-3-acetic acid (IAA) bound is considered a storage molecule and is inactive. However, some studies
have proposed an additional possible regulatory mechanism based on the ability of lectins to form
complexes with IAA. We report the first crystal structure of ConM in complex with IAA at 2.15 A resolution.
Based on a tetrameric model of the complex, we hypothesize how the lectin controls the availability
of IAA during the early seedling stages, indicating a possible new physiological role for these
proteins. A free indole group is also bound to the protein. The ConM interaction with different forms of
IAA is a strategy to render the phytohormone unavailable to the cell. Thus, this new physiological role
proposed for legume lectins might be a novel mechanism by which IAA levels are decreased in addition
to the destruction and formation of new complexes in the later stages of seed germination