The structure of the karrikin-insensitive protein (KAI2) in Arabidopsis thaliana

PLoS One. 2013;8(1):e54758. doi: 10.1371/journal.pone.0054758. Epub 2013 Jan 18.


KARRIKIN INSENSITIVE 2 (KAI2) is an α/β hydrolase involved in seed germination and seedling development. It is essential for plant responses to karrikins, a class of butenolide compounds derived from burnt plant material that are structurally similar to strigolactone plant hormones. The mechanistic basis for the function of KAI2 in plant development remains unclear. We have determined the crystal structure of Arabidopsis thaliana KAI2 in space groups P2(1) 2(1) 2(1) (a =63.57 Å, b =66.26 Å, c =78.25 Å) and P2(1) (a =50.20 Å, b =56.04 Å, c =52.43 Å, β =116.12°) to 1.55 and 2.11 Å respectively. The catalytic residues are positioned within a large hydrophobic pocket similar to that of DAD2, a protein required for strigolactone response in Petunia hybrida. KAI2 possesses a second solvent-accessible pocket, adjacent to the active site cavity, which offers the possibility of allosteric regulation. The structure of KAI2 is consistent with its designation as a serine hydrolase, as well as previous data implicating the protein in karrikin and strigolactone signalling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / chemistry*
  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis Proteins / chemistry*
  • Catalytic Domain
  • Crystallization
  • Crystallography, X-Ray*
  • Hydrolases / chemistry*
  • Hydrolases / genetics
  • Protein Conformation
  • Protein Structure, Secondary
  • Seedlings / chemistry*
  • Seedlings / genetics
  • Seedlings / growth & development


  • Arabidopsis Proteins
  • HTL protein, Arabidopsis
  • Hydrolases

Grant support

The authors gratefully acknowledge the Australian Research Council ( for funding (DP1096717, LP0882775, FT110100304). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.