Functional characterization of a potassium-selective prokaryotic glutamate receptor

Ionotropic glutamate receptor (iGluR) subunits contain a ϳ400-residue extracellular N-terminal domain ("X domain"), which is sequence-related to bacterial amino acid-binding proteins and to class C G-protein-coupled receptors. The X domain has been implicated in the assembly, transport to the cell surface, allosteric ligand binding, and desensitization in various members of the iGluR family, but its actual role in these events is poorly characterized. We have studied the properties of homomeric ␣-amino-3-hydroxy-5-methylisoxazolepropionate (AMPA)-selective GluR-D glutamate receptors carrying N-terminal deletions. Our analysis indicates that, surprisingly, transport to the cell surface, ligand binding properties, agonist-triggered channel activation, rapid desensitization, and allosteric potentiation by cyclothiazide can occur normally in the complete absence of the X domain (residues 22-402). The relatively intact ligand-gated channel function of a homomeric AMPA receptor in the absence of the X domain indirectly suggests more subtle roles for this domain in AMPA receptors, e.g. in the assembly of heteromeric receptors and in synaptic protein interactions.

Section: Discussionsupporting

confidence: 76%

Section: Discussionmentioning

confidence: 91%

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Channels Lacking the N-terminal Domain

Pasternack¹,

Coleman²,

Jouppila³

et al. 2002

“…Furthermore, the prokaryotic GluR0, which lacks the ATD, the M4 segment, as well as the CTD, and is presumably more ancient than mammalian iGluRs, exhibit slow gating kinetics (51). We therefore speculate that the emergence of the ATD, the M4, and the CTD later in evolution conferred additional efficiency to receptor tetramerization, thus allowing the LBD to evolve structural features required for fast gating.…”

Section: Discussionmentioning

confidence: 99%

The Transmembrane Domain Mediates Tetramerization of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors

Gan¹,

Dai

Zhou

et al. 2016

AMPA receptors (AMPARs) mediate fast excitatory neurotransmission in the central nervous system. Functional AMPARs are tetrameric complexes with a highly modular structure, consisting of four evolutionarily distinct structural domains: an amino-terminal domain (ATD), a ligand-binding domain (LBD), a channel-forming transmembrane domain (TMD), and a carboxyl-terminal domain (CTD). Here we show that the isolated TMD of the GluA1 AMPAR is fully capable of tetramerization. Additionally, removal of the extracellular domains from the receptor did not affect membrane topology or surface delivery. Furthermore, whereas the ATD and CTD contribute positively to tetramerization, the LBD presents a barrier to the process by reducing the stability of the receptor complex. These experiments pinpoint the TMD as the "tetramerization domain" for AMPARs, with other domains playing modulatory roles. They also raise intriguing questions about the evolution of iGluRs as well as the mechanisms regulating the biogenesis of AMPAR complexes.

“…The iGluRs internally contain ligandgated ion channels. Chen et al (16) have identified an iGluR, GluR0, from a prokaryote, the cyanobacterium Synechocystis. GluR0 has a hybrid structure between iGluRs and potassium channels and is thought to be a common ancestor for these molecular families.…”

Section: Discussionmentioning

confidence: 99%

A Metabotropic Glutamate Receptor Family Gene in Dictyostelium discoideum

Taniura

Sanada²,

Kuramoto³

et al. 2006

Metabotropic glutamate receptors (mGluRs) are a class of G-protein-coupled receptors that possess a seven transmembrane region involved in the modulation of excitatory synaptic transmission in the nervous system. mGluR orthologs have been identified in Drosophila, Caenorhabditis elegans, and higher organisms. Drosophila possesses two mGluR genes, DmGluRA and DmXR. We screened the Dictyostelium genome data base using the ligand binding domain of rat mGluR1 as bait, and identified a new receptor, DdmGluPR, belonging to the mGluR family. Similar to Drosophila DmXR, the residues of mGluRs involved in the binding of the ␣-carboxylic and ␣-amino groups of glutamate were well conserved in DdmGluPR, but the residues interacting with the ␥-carboxylic group of glutamate were not. The phylogenetic analysis suggests that DdmGluPR diverged after the mGluR family-GABA B receptors split but before mGluR family divergence. DdmGluPR mRNA was expressed in vegetative cells and throughout starvation-induced development, but the level of the expression was relatively high until 4 h after starvation. DdmGluPR was localized to the plasma membrane of axenically grown Ax-2 cells expressed as a green fluorescent protein fusion protein. DdmGluPR-null cells grew faster at high cell density and reached higher densities than wild-type cells. DdmGluPR-null cells exhibited delayed aggregates formation upon starvation and impaired chemotaxis toward cAMP. Although expressions of cAR1 and aca, cAMP-signaling components, were rapidly induced and peaked at 2-4 h in wild-type cells, DdmGluPRnull cells displayed sustained and peaked at 8 h of the expressions of these genes. Our findings suggest the involvement of DdmGluPR in the early development of Dictyostelium discoideum. Metabotropic glutamate receptors (mGluRs)4 are a class of G-protein-coupled receptors (GPCRs) that possess a seven-transmembrane region and couple with second messenger systems including phosphoinositide hydrolysis and regulation of adenylate cyclase activation. mGluRs are key receptors in the modulation of excitatory synaptic transmission in the central nervous system. The eight subtypes of mGluRs are classified into three subgroups according to sequence similarity, agonist selectivity, and effector system differences: subgroup I (mGluR1 and -5), subgroup II (mGluR2 and -3), and subgroup III (mGluR4, -6, -7, and -8) (1). The mGluR structure is divided into three regions: the extracellular region, the seven-transmembrane spanning region, and the cytoplasmic region (2). The extracellular region is further divided into the ligand binding domain (LBD) and the cysteine-rich region. They share sequence similarity with the calcium-sensing receptor (3) and the pheromone receptor (4, 5) to form the mGluR family. The primary structure and pharmacology of mGluRs are evolutionarily well conserved in Drosophila, Caenorhabditis elegans, and higher mammals. Sequence analysis of the C. elegans genome reveals the presence of one homologue for each group (6). Two kinds of mGluRs, DmGluRA and DmXR...