The plant hormone abscisic acid (ABA) has a central role in coordinating the adaptive response in situations of decreased water availability as well as the regulation of plant growth and development. Recently, a 14-member family of intracellular ABA receptors, named PYR/PYL/RCAR1,2,3, has been identified. These proteins inhibit in an ABA-dependent manner the activity of a family of key negative regulators of the ABA signalling pathway: the group-A protein phosphatases type 2C (PP2Cs)4,5,6. Here we present the crystal structure of Arabidopsis thaliana PYR1, which consists of a dimer in which one of the subunits is bound to ABA. In the ligand-bound subunit, the loops surrounding the entry to the binding cavity fold over the ABA molecule, enclosing it inside, whereas in the empty subunit they form a channel leaving an open access to the cavity, indicating that conformational changes in these loops have a critical role in the stabilization of the hormone–receptor complex. By providing structural details on the ABA-binding pocket, this work paves the way for the development of new small molecules able to activate the plant stress response.
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We thank A. McArthy and S. Brockhauser for support during X-ray data collection and R. Serrano and S. Cusack for critical reading of the manuscript. We are grateful to the European Synchrotron radiation facility (ESRF) and the EMBL for access to the macromolecular crystallography and BioSAXS beamlines. This work was supported by grant BIO2008-00221 from Ministerio de Educación y Ciencia and Fondo Europeo de Desarrollo Regional and Consejo Superior de Investigaciones Científicas (fellowships to J.S. and R.A.). Access to the high throughput crystallization facility of the Partnership for Structural Biology in Grenoble (PSB) (https://htxlab.embl.fr) was supported by the European Community–Research Infrastructure Action PCUBE under the FP7 ‘Capacities’ specific programme.
Author Contributions J.S. contributed with the cloning, protein purification, ITC, MALLS and helped with crystallization and SAXS experiments. F.D. performed protein purification, crystallization and crystal refinement experiments and helped with X-ray data collection. A.R. supervised SAXS data collection and performed data analysis. M.J. carried out MALLS experiments and analysis. R.A. carried out cloning and protein purification. S.-Y.P. and S.R.C. carried out cloning of mutant PYR1 proteins and contributed to discussions. P.L.R. contributed to discussions and writing of the manuscript. J.A.M. supervised the work and performed data collection, structure solution and refinement as well as writing of the manuscript.
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Santiago, J., Dupeux, F., Round, A. et al. The abscisic acid receptor PYR1 in complex with abscisic acid . Nature 462, 665–668 (2009). https://doi.org/10.1038/nature08591
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