Structural Insights into the Abscisic Acid Stereospecificity by the ABA Receptors PYR/PYL/RCAR |
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| Authors: | Xingliang Zhang Lun Jiang Guoqiang Wang Lin Yu Qi Zhang Qi Xin Wei Wu Zhizhong Gong Zhongzhou Chen |
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| Affiliation: | 1. State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China.; 2. Clinical Medicine Research Center, Affiliated Hospital of Guangdong Medical College, Guangdong, China.; 3. State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing, China.; Van Andel Research Institute, United States of America, |
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| Abstract: | The phytohormone abscisic acid ((+)-ABA) plays a key role in many processes. The biological and biochemical activities of unnatural (−)-ABA have been extensively investigated since 1960s. However, the recognition mechanism by which only a few members among PYR/PYL/RCAR (PYLs) family can bind (−)-ABA remains largely unknown. Here we systematically characterized the affinity of PYLs binding to the (−)-ABA and reported the crystal structures of apo-PYL5, PYL3-(−)-ABA and PYL9-(+)-ABA. PYL5 showed the strongest binding affinity with (−)-ABA among all the PYLs. PYL9 is a stringently exclusive (+)-ABA receptor with interchangeable disulfide bonds shared by a subclass of PYLs. PYL3 is a dual receptor to both ABA enantiomers. The binding orientation and pocket of (−)-ABA in PYLs are obviously different from those of (+)-ABA. Steric hindrance and hydrophobic interaction are the two key factors in determining the stereospecificity of PYLs binding to (−)-ABA, which is further confirmed by gain-of-function and loss-of-function mutagenesis. Our results provide novel insights of the bioactivity of ABA enantiomers onto PYLs, and shed light on designing the selective ABA receptors agonists. |
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