Structural basis of steroid hormone perception by the receptor kinase BRI1

Nature. 2011 Jun 12;474(7352):467-71. doi: 10.1038/nature10153.


Polyhydroxylated steroids are regulators of body shape and size in higher organisms. In metazoans, intracellular receptors recognize these molecules. Plants, however, perceive steroids at membranes, using the membrane-integral receptor kinase BRASSINOSTEROID INSENSITIVE 1 (BRI1). Here we report the structure of the Arabidopsis thaliana BRI1 ligand-binding domain, determined by X-ray diffraction at 2.5 Å resolution. We find a superhelix of 25 twisted leucine-rich repeats (LRRs), an architecture that is strikingly different from the assembly of LRRs in animal Toll-like receptors. A 70-amino-acid island domain between LRRs 21 and 22 folds back into the interior of the superhelix to create a surface pocket for binding the plant hormone brassinolide. Known loss- and gain-of-function mutations map closely to the hormone-binding site. We propose that steroid binding to BRI1 generates a docking platform for a co-receptor that is required for receptor activation. Our findings provide insight into the activation mechanism of this highly expanded family of plant receptors that have essential roles in hormone, developmental and innate immunity signalling.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / chemistry*
  • Arabidopsis / metabolism
  • Arabidopsis Proteins / chemistry*
  • Arabidopsis Proteins / metabolism*
  • Binding Sites
  • Brassinosteroids
  • Cholestanols / chemistry
  • Cholestanols / metabolism*
  • Crystallography, X-Ray
  • Enzyme Activation
  • Models, Molecular
  • Molecular Sequence Data
  • Plant Growth Regulators / chemistry
  • Plant Growth Regulators / metabolism*
  • Protein Binding
  • Protein Kinases / chemistry*
  • Protein Kinases / metabolism*
  • Protein Multimerization
  • Protein Structure, Tertiary
  • Steroids, Heterocyclic / chemistry
  • Steroids, Heterocyclic / metabolism*
  • Structure-Activity Relationship


  • Arabidopsis Proteins
  • Brassinosteroids
  • Cholestanols
  • Plant Growth Regulators
  • Steroids, Heterocyclic
  • Protein Kinases
  • BRI1 protein, Arabidopsis
  • brassinolide

Associated data

  • PDB/3RIZ
  • PDB/3RJ0