The cys-loop ligand-gated ion channel gene superfamily of the nematode, Caenorhabditis elegans.
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ABSTRACT:
SUBMITTER: Jones AK
PROVIDER: S-EPMC2257991 | biostudies-literature | 2008 Mar
REPOSITORIES: biostudies-literature
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The cys-loop ligand-gated ion channel gene superfamily of the nematode, Caenorhabditis elegans.
Jones Andrew K AK Sattelle David B DB
Invertebrate neuroscience : IN 20080221 1
The nematode, Caenorhabditis elegans, possesses the most extensive known superfamily of cys-loop ligand-gated ion channels (cys-loop LGICs) consisting of 102 subunit-encoding genes. Less than half of these genes have been functionally characterised which include cation-permeable channels gated by acetylcholine (ACh) and gamma-aminobutyric acid (GABA) as well as anion-selective channels gated by ACh, GABA, glutamate and serotonin. Following the guidelines set for genetic nomenclature for C. elega ...[more]
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Project description:BackgroundMembers of the cys-loop ligand-gated ion channel (cys-loop LGIC) superfamily mediate chemical neurotransmission and are studied extensively as potential targets of drugs used to treat neurological disorders such as Alzheimer's disease. Insect cys-loop LGICs are also of interest as they are targets of highly successful insecticides. The red flour beetle, Tribolium castaneum, is a major pest of stored agricultural products and is also an important model organism for studying development.ResultsAs part of the T. castaneum genome sequencing effort, we have characterized the beetle cys-loop LGIC superfamily which is the third insect superfamily to be described after those of Drosophila melanogaster and Apis mellifera, and also the largest consisting of 24 genes. As with Drosophila and Apis, Tribolium possesses ion channels gated by acetylcholine, gamma-amino butyric acid (GABA), glutamate and histamine as well as orthologs of the Drosophila pH-sensitive chloride channel subunit (pHCl), CG8916 and CG12344. Similar to Drosophila and Apis, Tribolium cys-loop LGIC diversity is broadened by alternative splicing although the beetle orthologs of RDL and GluCl possess more variants of exon 3. Also, RNA A-to-I editing was observed in two Tribolium nicotinic acetylcholine receptor subunits, Tcasalpha6 and Tcasbeta1. Editing in Tcasalpha6 is evolutionarily conserved with D. melanogaster, A. mellifera and Heliothis virescens, whereas Tcasbeta1 is edited at a site so far only observed in the beetle.ConclusionOur findings reveal that in diverse insect species the cys-loop LGIC superfamily has remained compact with only minor changes in gene numbers. However, alternative splicing, RNA editing and the presence of divergent subunits broadens the cys-loop LGIC proteome and generates species-specific receptor isoforms. These findings on Tribolium castaneum enhance our understanding of cys-loop LGIC functional genomics and provide a useful basis for the development of improved insecticides that target an important agricultural pest.
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Project description:Prior to the advent of synthetic nematocides, natural products such as seaweed were used to control nematode infestations. The nematocidal agent in seaweed is betaine, an amino acid that functions as an osmolyte and methyl donor. However, the molecular mechanisms of betaine toxicity are unknown. We identified the betaine transporter SNF-3 and the betaine receptor ACR-23 in the nematode C. elegans. Mutating snf-3 in a sensitized background caused the worms to be hypercontracted and paralyzed, presumably as a result of excess extracellular betaine. These behavioral defects were suppressed by mutations in acr-23, which encodes a ligand-gated cation channel of the cys-loop family. ACR-23 was activated by betaine and functioned in the mechanosensory neurons to maintain basal levels of locomotion. However, overactivation of the receptor by excess betaine or by the allosteric modulator monepantel resulted in hypercontraction and death of the nematode. Thus, monepantel targets a betaine signaling pathway in nematodes.
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Project description:Ligand-gated ion channels (LGICs) are important regulators of neuromuscular function, making them attractive antiparasitic drug targets. While roundworm LGICs are targeted by several anthelmintic classes, flatworm LGICs are less studied. Chromosome-level genome assemblies have recently been released for Schistosoma flatworm species that cause the disease schistosomiasis. These have allowed us to comprehensively predict schistosome LGICs, adding to prior annotations. Analysis of LGIC sequences revealed a clade of receptors lacking cysteines at the eponymous Cys-loop region of the channel. Since these atypical channels are divergent from mammalian LGICs, they may be promising targets to treat diseases caused by parasitic flatworms.
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Project description:The superfamily of pentameric ligand-gated ion channels includes neurotransmitter receptors that mediate fast synaptic transmission in vertebrates, and are targets for drugs including alcohols, anesthetics, benzodiazepines, and anticonvulsants. However, the mechanisms of ion channel opening, gating, and modulation in these receptors leave many open questions, despite their pharmacological importance. Subtle conformational changes in both the extracellular and transmembrane domains are likely to influence channel opening, but have been difficult to characterize given the limited structural data available for human membrane proteins. Recent crystal structures of a modified Caenorhabditis elegans glutamate-gated chloride channel (GluCl) in multiple states offer an appealing model system for structure-function studies. However, the pharmacology of the crystallographic GluCl construct is not well established. To establish the functional relevance of this system, we used two-electrode voltage-clamp electrophysiology in Xenopus oocytes to characterize activation of crystallographic and native-like GluCl constructs by L-glutamate and ivermectin. We also tested modulation by ethanol and other anesthetic agents, and used site-directed mutagenesis to explore the role of a region of Loop F which was implicated in ligand gating by molecular dynamics simulations. Our findings indicate that the crystallographic construct functionally models concentration-dependent agonism and allosteric modulation of pharmacologically relevant receptors. Specific substitutions at residue Leu174 in loop F altered direct L-glutamate activation, consistent with computational evidence for this region's role in ligand binding. These insights demonstrate conservation of activation and modulation properties in this receptor family, and establish a framework for GluCl as a model system, including new possibilities for drug discovery. In this study, we elucidate the validity of a modified glutamate-gated chloride channel (GluClcryst ) as a structurally accessible model for GABAA receptors. In contrast to native-like controls, GluClcryst exhibits classical activation by its neurotransmitter ligand L-glutamate. The modified channel is also sensitive to allosteric modulators associated with human GABAA receptors, and to site-directed mutations predicted to alter channel opening.
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