Structural insights into the mechanism of abscisic acid signaling by PYL proteins. Author Ping Yin, He Fan, Qi Hao, Xiaoqiu Yuan, Di Wu, Yuxuan Pang, Chuangye Yan, Wenqi Li, Jiawei Wang, Nieng Yan Publication Year 2009 Type Journal Article Abstract Abscisic acid (ABA) is an important phytohormone that regulates plant stress responses. Proteins from the PYR-PYL-RCAR family were recently identified as ABA receptors. Upon binding to ABA, a PYL protein associates with type 2C protein phosphatases (PP2Cs) such as ABI1 and ABI2, inhibiting their activity; the molecular mechanisms by which PYLs mediate ABA signaling remain unknown, however. Here we report three crystal structures: apo-PYL2, (+)-ABA-bound PYL2 and (+)-ABA-bound PYL1 in complex with phosphatase ABI1. Apo-PYL2 contains a pocket surrounded by four highly conserved surface loops. In response to ABA binding, loop CL2 closes onto the pocket, creating a surface that recognizes ABI1. In the ternary complex, the CL2 loop is located near the active site of ABI1, blocking the entry of substrate proteins. Together, our data reveal the mechanisms by which ABA regulates PYL-mediated inhibition of PP2Cs. Keywords Models, Biological, Signal Transduction, Protein Binding, Models, Molecular, Protein Structure, Tertiary, Crystallography, X-Ray, Carrier Proteins, Arabidopsis Proteins, Protein Structure, Quaternary, Abscisic Acid, Phosphoprotein Phosphatases, Plant Growth Regulators Journal Nat Struct Mol Biol Volume 16 Issue 12 Pages 1230-6 Date Published 2009 Dec ISSN Number 1545-9985 DOI 10.1038/nsmb.1730 Alternate Journal Nat Struct Mol Biol PMID 19893533 PubMedGoogle ScholarBibTeXEndNote X3 XML