Structural Basis for flg22-induced Activation of the Arabidopsis FLS2-BAK1 Immune Complex

Science. 2013 Nov 1;342(6158):624-8. doi: 10.1126/science.1243825. Epub 2013 Oct 10.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antigen-Antibody Complex / chemistry*
  • Arabidopsis / immunology*
  • Arabidopsis Proteins / chemistry*
  • Crystallography, X-Ray
  • Flagellin / chemistry*
  • Protein Kinases / chemistry*
  • Protein Structure, Tertiary
  • Protein-Serine-Threonine Kinases / chemistry*


  • Antigen-Antibody Complex
  • Arabidopsis Proteins
  • Flagellin
  • Protein Kinases
  • BAK1 protein, Arabidopsis
  • FLS2 protein, Arabidopsis
  • Protein-Serine-Threonine Kinases

Associated data

  • PDB/4MN8
  • PDB/4MNA