Smoke-derived karrikin perception by the α/β-hydrolase KAI2 from Arabidopsis

Proc Natl Acad Sci U S A. 2013 May 14;110(20):8284-9. doi: 10.1073/pnas.1306265110. Epub 2013 Apr 23.


Genetic studies in Arabidopsis implicate an α/β-hydrolase, KARRIKIN-INSENSITIVE 2 (KAI2) as a receptor for karrikins, germination-promoting butenolide small molecules found in the smoke of burned plants. However, direct biochemical evidence for the interaction between KAI2 and karrikin and for the mechanism of downstream signaling by a KAI2-karrikin complex remain elusive. We report crystallographic analyses and ligand-binding experiments for KAI2 recognition of karrikins. The karrikin-1 (KAR1) ligand sits in the opening to the active site abutting a helical domain insert but distal from the canonical catalytic triad (Ser95-His246-Asp217) of α/β-hydrolases, consistent with the lack of detectable hydrolytic activity by purified KAI2. The closest approach of KAR1 to Ser95-His246-Asp217 is 3.8 Å from His246. Six aromatic side chains, including His246, encapsulate KAR1 through geometrically defined aromatic-aromatic interactions. KAR1 binding induces a conformational change in KAI2 at the active site entrance. A crevice of hydrophobic residues linking the polar edge of KAR1 and the helical domain insert suggests that KAI2-KAR1 creates a contiguous interface for binding signaling partners in a ligand-dependent manner.

Keywords: plant signaling; seed dormancy; wildfires.

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 / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Catalytic Domain
  • Crystallography, X-Ray
  • Escherichia coli / metabolism
  • Fires
  • Furans / metabolism*
  • Hydrolases / genetics
  • Hydrolases / metabolism*
  • Hydrolysis
  • Hydrophobic and Hydrophilic Interactions
  • Ligands
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Protein Binding
  • Protein Structure, Tertiary
  • Pyrans / metabolism*
  • Seeds / metabolism
  • Signal Transduction
  • Smoke*


  • 3-methyl-2H-furo(2,3-c)pyran-2-one
  • Arabidopsis Proteins
  • Furans
  • Ligands
  • Pyrans
  • Smoke
  • HTL protein, Arabidopsis
  • Hydrolases

Associated data

  • PDB/4JYM
  • PDB/4JYP