title: Mechanism of high-affinity abscisic acid binding to PYL9/RCAR1.
abstract: Arabidopsis receptors of abscisic acid (ABA), the key plant hormone for adaptation to water stress, comprise 14 PYR/PYLs/RCARs proteins classified into three subfamilies I, II, and III, which suggests functional differentiation. Although their monomer-dimer equilibria may be correlated with differences in their ABA-binding affinities, how the dimerization decreases the affinity is unclear. Comparative structural and binding studies between PYL9, which is a representative of high-affinity subfamily I, and low-affinity members of subfamily III reveals that the nonpolar triplet (Ile110, Val162, and Leu165) and Pro64 contribute to enhance ABA-binding affinity by inducing a shift of the ABA carboxyl group to form additional direct hydrogen bonds with conserved Asn169. Our mutation studies of PYL1 successfully produced a monomeric mutant PYL1 exhibiting low ABA affinity and also a dimeric mutant PYL1 exhibiting high ABA-binding affinity, suggesting that dimer formation of ABA receptors is not essential for their low ABA-binding affinity. Our study contributes toward establishing the structural basis for the higher ABA-binding affinity of the subfamily receptors and provides a clue for understanding the broad spectrum of hormone actions in plants manifested by the different hormone-binding affinity of multiple receptors.
authors.affiliation: Structural Biology Laboratory, Nara Institute of Science and Technology, 8916-5, Takayama, Ikoma, Nara, 630-0192, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Nakagawa
authors.forename: Megumi
authors.initials: M
authors.lastname: Kagiyama
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Shibata
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Hirano
authors.forename: Toshio
authors.initials: T
authors.lastname: Hakoshima
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D055503:Protein Multimerization
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C540972:RCAR1 protein, Arabidopsis; D000040:Abscisic Acid