title: Structural insights into the negative regulation of BRI1 signaling by BRI1-interacting protein BKI1.
abstract: Brassinosteroids (BRs) are essential steroid hormones that have crucial roles in plant growth and development. BRs are perceived by the cell-surface receptor-like kinase brassinosteroid insensitive 1 (BRI1). In the absence of BRs, the cytosolic kinase domain (KD) of BRI1 is inhibited by its auto-inhibitory carboxyl terminus, as well as by interacting with an inhibitor protein, BRI1 kinase inhibitor 1 (BKI1). How BR binding to the extracellular domain of BRI1 leads to activation of the KD and dissociation of BKI1 into the cytosol remains unclear. Here we report the crystal structure of BRI1 KD in complex with the interacting peptide derived from BKI1. We also provide biochemical evidence that BRI1-associated kinase 1 (BAK1) plays an essential role in initiating BR signaling. Steroid-dependent heterodimerization of BRI1 and BAK1 ectodomains brings their cytoplasmic KDs in the right orientation for competing with BKI1 and transphosphorylation.
authors.affiliation: MOE Key Laboratory for Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Genetic Engineering and Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Jiang
authors.affiliation: MOE Key Laboratory for Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Jue
authors.initials: J
authors.lastname: Wang
authors.affiliation: MOE Key Laboratory for Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Chen
authors.affiliation: MOE Key Laboratory for Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Shi-Long
authors.initials: SL
authors.lastname: Fan
authors.affiliation: MOE Key Laboratory for Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Jia-Wei
authors.initials: JW
authors.lastname: Wu
authors.affiliation: 1] State Key Laboratory of Genetic Engineering and Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China [2] College of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, China.
authors.forename: Xuelu
authors.initials: X
authors.lastname: Wang
authors.affiliation: MOE Key Laboratory for Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Zhi-Xin
authors.initials: ZX
authors.lastname: Wang
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D062105:Molecular Docking Simulation; D008969:Molecular Sequence Data; D010641:Phenotype; D010766:Phosphorylation; D030821:Plants, Genetically Modified / Q000378:metabolism; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; C513107:BKI1 protein, Arabidopsis; D011494:Protein Kinases; C108270:BRI1 protein, Arabidopsis