title: Structural mechanism of abscisic acid binding and signaling by dimeric PYR1.
abstract: The phytohormone abscisic acid (ABA) acts in seed dormancy, plant development, drought tolerance, and adaptive responses to environmental stresses. Structural mechanisms mediating ABA receptor recognition and signaling remain unknown but are essential for understanding and manipulating abiotic stress resistance. Here, we report structures of pyrabactin resistance 1 (PYR1), a prototypical PYR/PYR1-like (PYL)/regulatory component of ABA receptor (RCAR) protein that functions in early ABA signaling. The crystallographic structure reveals an alpha/beta helix-grip fold and homodimeric assembly, verified in vivo by coimmunoprecipitation. ABA binding within a large internal cavity switches structural motifs distinguishing ABA-free "open-lid" from ABA-bound "closed-lid" conformations. Small-angle x-ray scattering suggests that ABA signals by converting PYR1 to a more compact, symmetric closed-lid dimer. Site-directed PYR1 mutants designed to disrupt hormone binding lose ABA-triggered interactions with type 2C protein phosphatase partners in planta.
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California at San Diego, La Jolla, CA 92093, USA.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nishimura
authors.forename: Kenichi
authors.initials: K
authors.lastname: Hitomi
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Arvai
authors.forename: Robert P
authors.initials: RP
authors.lastname: Rambo
authors.forename: Chiharu
authors.initials: C
authors.lastname: Hitomi
authors.forename: Sean R
authors.initials: SR
authors.lastname: Cutler
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
authors.forename: Elizabeth D
authors.initials: ED
authors.lastname: Getzoff
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D047468:Immunoprecipitation; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D053838:Scattering, Small Angle; D015398:Signal Transduction; D014961:X-Ray Diffraction
chemical_list: D029681:Arabidopsis Proteins; D026901:Membrane Transport Proteins; D050505:Mutant Proteins; D021122:Protein Subunits; C540976:AT4G17870 protein, Arabidopsis; D000040:Abscisic Acid; C087434:ABI1 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases