The structural bases for agonist diversity in an Arabidopsis thaliana glutamate receptor-like channel

Proc Natl Acad Sci U S A. 2020 Jan 7;117(1):752-760. doi: 10.1073/pnas.1905142117. Epub 2019 Dec 23.


Arabidopsis thaliana glutamate receptor-like (GLR) channels are amino acid-gated ion channels involved in physiological processes including wound signaling, stomatal regulation, and pollen tube growth. Here, fluorescence microscopy and genetics were used to confirm the central role of GLR3.3 in the amino acid-elicited cytosolic Ca2+ increase in Arabidopsis seedling roots. To elucidate the binding properties of the receptor, we biochemically reconstituted the GLR3.3 ligand-binding domain (LBD) and analyzed its selectivity profile; our binding experiments revealed the LBD preference for l-Glu but also for sulfur-containing amino acids. Furthermore, we solved the crystal structures of the GLR3.3 LBD in complex with 4 different amino acid ligands, providing a rationale for how the LBD binding site evolved to accommodate diverse amino acids, thus laying the grounds for rational mutagenesis. Last, we inspected the structures of LBDs from nonplant species and generated homology models for other GLR isoforms. Our results establish that GLR3.3 is a receptor endowed with a unique amino acid ligand profile and provide a structural framework for engineering this and other GLR isoforms to investigate their physiology.

Keywords: Ca2+ signaling; GLR channels; X-ray crystallography; binding assay; modeling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acids / metabolism*
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / agonists
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Arabidopsis Proteins / ultrastructure*
  • Binding Sites / genetics
  • Calcium / metabolism
  • Crystallography, X-Ray
  • Cytosol / metabolism
  • Ligands
  • Mutation
  • Plant Roots / metabolism
  • Plants, Genetically Modified
  • Protein Domains / genetics*
  • Receptors, Glutamate / genetics
  • Receptors, Glutamate / metabolism
  • Receptors, Glutamate / ultrastructure*
  • Seedlings / metabolism
  • Structure-Activity Relationship


  • Amino Acids
  • Arabidopsis Proteins
  • GLR3.3 protein, Arabidopsis
  • Ligands
  • Receptors, Glutamate
  • Calcium

Associated data

  • PDB/6R85
  • PDB/6R88
  • PDB/6R89
  • PDB/6R8A