The Arabidopsis thaliana Glutamate-like Receptor Family (AtGLR) - Communication in Plants: Neuronal Aspects of Plant Life - page 188

Fig. 13.1. Arabidopsis thaliana glutamate-like receptors ( At GLRs) are predicted to share
the ionotropic glutamate receptor (iGluR) channel structure, with three transmembrane
domains ( M 1, M 2, M 3) and a P domain forming a membrane-embedded pore loop when
subunits combine into a functional tetramer (Colquhoun and Sivilotti 2004). At GLRs also
share with iGluRs a similar putative ligand-binding motif formed by the interactions of
the S1 and S2 domains. Most At GLRs sequence before the S 1andafter S 2, including M3,
which is absent in Synechocystis GluR0, show limited sequence similarity to iGluR (Chiu et
al. 2002). Both At GLR and iGluR have long N-terminal domains (N-term) with similarity
to bacterial periplasmic binding proteins (PBP); the role of the N-terminus is not clearly
defined but it is thought to be involved in targeting, translocation and degradation (Kato et
al. 2005). P is confusingly sometimes referred to as M2; therefore, M2 and M3 domains are
then named M3 and M4, respectively; S1 and S2 have been called GlnH1 and GlnH2

In animals, iGluR subunits are generally non-selective cation channels
(NSCCs) that propagate impulses across vertebrate neuronal or invertebrate
neuromuscular junctions through glutamate-gated Na + and/or Ca 2+ entry
(Dingledene et al. 1999). iGluR subunits can be grouped into seven subfam-
ilies according to primary amino acid sequence which have been further
classifiedintofourreceptorfamiliesaccordingtotheirsensitivitytospecific
amino acids and electrophysiological as well as pharmacological proper-
ties [GluR

α α (GluR1-4); -amino-3-hydroxy-5-methyl-4-isoxazole propi-

β γ δ onic acid, AMPA], [GluR (GluR5-7), GluR (KA1,2); kainate], [GluR

δ ε ζ χ ( (NR3A,B); N -

methyl-D-aspartate, NMDA] (Hollmann and Heinemann 1994; Sprengel

1,2); orphan], [GluR (NR2A-D), GluR (NR1), GluR