Crystal structure of the leucine-rich repeat ectodomain of the plant immune receptor kinase SOBIR1

Acta Crystallogr D Struct Biol. 2019 May 1;75(Pt 5):488-497. doi: 10.1107/S2059798319005291. Epub 2019 Apr 29.


Plant-unique membrane receptor kinases with leucine-rich repeat (LRR) extracellular domains are key regulators of development and immune responses. Here, the 1.55 Å resolution crystal structure of the immune receptor kinase SOBIR1 from Arabidopsis is presented. The ectodomain structure reveals the presence of five LRRs sandwiched between noncanonical capping domains. The disulfide-bond-stabilized N-terminal cap harbours an unusual β-hairpin structure. The C-terminal cap features a highly positively charged linear motif which was found to be largely disordered in this structure. Size-exclusion chromatography and right-angle light-scattering experiments suggest that SOBIR1 is a monomer in solution. The protruding β-hairpin, a set of highly conserved basic residues at the inner surface of the SOBIR LRR domain and the presence of a genetic missense allele in LRR2 together suggest that the SOBIR1 ectodomain may mediate protein-protein interaction in plant immune signalling.

Keywords: Arabidopsis; cell signalling; ectodomain; leucine-rich repeat; membrane receptor; plant immune signalling; receptor kinase.

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis Proteins / chemistry*
  • Crystallography, X-Ray
  • Leucine / chemistry*
  • Models, Molecular
  • Protein Binding
  • Protein Conformation
  • Protein Domains
  • Protein Kinases / chemistry*
  • Protein Serine-Threonine Kinases / chemistry*
  • Protein Serine-Threonine Kinases / metabolism


  • Arabidopsis Proteins
  • Protein Kinases
  • SOBIR protein, Arabidopsis
  • Protein Serine-Threonine Kinases
  • Leucine