The abscisic acid receptor PYR1 in complex with abscisic acid.
Santiago, Julia 1,5; Dupeux, Florine 2,5; Round, Adam 2; Antoni, Regina 1; Park, Sang-Youl 3; Jamin, Marc 4; Cutler, Sean R. 3; Rodriguez, Pedro Luis 1; Marquez, Jose Antonio 2,*
[Letter] Nature. 462(7273):665-668, December 3, 2009.

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: 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/RCAR 1-3, 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) 4-6. 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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