title: Structural basis for flg22-induced activation of the Arabidopsis FLS2-BAK1 immune complex.
abstract: Flagellin perception in Arabidopsis is through recognition of its highly conserved N-terminal epitope (flg22) by flagellin-sensitive 2 (FLS2). Flg22 binding induces FLS2 heteromerization with BRASSINOSTEROID INSENSITIVE 1-associated kinase 1 (BAK1) and their reciprocal activation followed by plant immunity. Here, we report the crystal structure of FLS2 and BAK1 ectodomains complexed with flg22 at 3.06 angstroms. A conserved and a nonconserved site from the inner surface of the FLS2 solenoid recognize the C- and N-terminal segment of flg22, respectively, without oligomerization or conformational changes in the FLS2 ectodomain. Besides directly interacting with FLS2, BAK1 acts as a co-receptor by recognizing the C terminus of the FLS2-bound flg22. Our data reveal the molecular mechanisms underlying FLS2-BAK1 complex recognition of flg22 and provide insight into the immune receptor complex activation.
authors.affiliation: School of Life Sciences, Tsinghua University, Beijing 100084, China, and Tsinghua-Peking Center for Life Sciences, Beijing 100084, China.
authors.forename: Yadong
authors.initials: Y
authors.lastname: Sun
authors.forename: Lei
authors.initials: L
authors.lastname: Li
authors.forename: Alberto P
authors.initials: AP
authors.lastname: Macho
authors.forename: Zhifu
authors.initials: Z
authors.lastname: Han
authors.forename: Zehan
authors.initials: Z
authors.lastname: Hu
authors.forename: Cyril
authors.initials: C
authors.lastname: Zipfel
authors.forename: Jian-Min
authors.initials: JM
authors.lastname: Zhou
authors.forename: Jijie
authors.initials: J
authors.lastname: Chai
mesh_terms: D000936:Antigen-Antibody Complex / Q000737:chemistry*; D017360:Arabidopsis / Q000276:immunology*; D029681:Arabidopsis Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005408:Flagellin / Q000737:chemistry*; D011494:Protein Kinases / Q000737:chemistry*; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry*; D017434:Protein Structure, Tertiary
chemical_list: D000936:Antigen-Antibody Complex; D029681:Arabidopsis Proteins; D005408:Flagellin; D011494:Protein Kinases; C463660:BAK1 protein, Arabidopsis; C411853:FLS2 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases