Mechanism of auxin perception by the TIR1 ubiquitin ligase

Nature. 2007 Apr 5;446(7136):640-5. doi: 10.1038/nature05731.

Abstract

Auxin is a pivotal plant hormone that controls many aspects of plant growth and development. Perceived by a small family of F-box proteins including transport inhibitor response 1 (TIR1), auxin regulates gene expression by promoting SCF ubiquitin-ligase-catalysed degradation of the Aux/IAA transcription repressors, but how the TIR1 F-box protein senses and becomes activated by auxin remains unclear. Here we present the crystal structures of the Arabidopsis TIR1-ASK1 complex, free and in complexes with three different auxin compounds and an Aux/IAA substrate peptide. These structures show that the leucine-rich repeat domain of TIR1 contains an unexpected inositol hexakisphosphate co-factor and recognizes auxin and the Aux/IAA polypeptide substrate through a single surface pocket. Anchored to the base of the TIR1 pocket, auxin binds to a partially promiscuous site, which can also accommodate various auxin analogues. Docked on top of auxin, the Aux/IAA substrate peptide occupies the rest of the TIR1 pocket and completely encloses the hormone-binding site. By filling in a hydrophobic cavity at the protein interface, auxin enhances the TIR1-substrate interactions by acting as a 'molecular glue'. Our results establish the first structural model of a plant hormone receptor.

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

  • Arabidopsis / enzymology
  • Arabidopsis / metabolism
  • Arabidopsis Proteins / chemistry*
  • Arabidopsis Proteins / metabolism*
  • Binding Sites
  • Crystallography, X-Ray
  • F-Box Proteins / chemistry*
  • F-Box Proteins / metabolism*
  • Indoleacetic Acids / chemistry
  • Indoleacetic Acids / metabolism*
  • Models, Molecular
  • Phytic Acid / metabolism
  • Plant Growth Regulators / chemistry
  • Plant Growth Regulators / metabolism
  • Protein Structure, Tertiary
  • Receptors, Cell Surface / chemistry*
  • Receptors, Cell Surface / metabolism*
  • Structure-Activity Relationship
  • Substrate Specificity
  • Ubiquitin-Protein Ligases / chemistry*
  • Ubiquitin-Protein Ligases / metabolism*

Substances

  • ASK1 protein, Arabidopsis
  • Arabidopsis Proteins
  • F-Box Proteins
  • Indoleacetic Acids
  • Plant Growth Regulators
  • Receptors, Cell Surface
  • TIR1 protein, Arabidopsis
  • Phytic Acid
  • Ubiquitin-Protein Ligases

Associated data

  • PDB/2P1M
  • PDB/2P1N
  • PDB/2P1O
  • PDB/2P1P
  • PDB/2P1Q