A common allosteric mechanism regulates homeostatic inactivation of auxin and gibberellin
Sayaka Takehara, Shun Sakuraba, Bunzo Mikami, Hideki Yoshida, Hisako Yoshimura, Aya Itoh, M. Endo, Nobuhisa Watanabe, T. Nagae, Makoto Matsuoka, Miyako Ueguchi‐Tanaka
Abstract
Abstract Allosteric regulation is protein activation by effector binding at a site other than the active site. Here, we show via X-ray structural analysis of gibberellin 2-oxidase 3 (GA2ox3), and auxin dioxygenase (DAO), that such a mechanism maintains hormonal homeostasis in plants. Both enzymes form multimers by interacting via GA 4 and indole-3-acetic acid (IAA) at their binding interface. Via further functional analyses we reveal that multimerization of these enzymes gradually proceeds with increasing GA 4 and IAA concentrations; multimerized enzymes have higher specific activities than monomer forms, a system that should favour the maintenance of homeostasis for these phytohormones. Molecular dynamic analysis suggests a possible mechanism underlying increased GA2ox3 activity by multimerization—GA 4 in the interface of oligomerized GA2ox3s may be able to enter the active site with a low energy barrier. In summary, homeostatic systems for maintaining GA and IAA levels, based on a common allosteric mechanism, appear to have developed independently.