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Modulation of a rapid neurotransmitter receptor-ion channel by membrane lipids.

ABSTRACT: Membrane lipids modulate the proteins embedded in the bilayer matrix by two non-exclusive mechanisms: direct or indirect. The latter comprise those effects mediated by the physicochemical state of the membrane bilayer, whereas direct modulation entails the more specific regulatory effects transduced via recognition sites on the target membrane protein. The nicotinic acetylcholine receptor (nAChR), the paradigm member of the pentameric ligand-gated ion channel (pLGIC) superfamily of rapid neurotransmitter receptors, is modulated by both mechanisms. Reciprocally, the nAChR protein exerts influence on its surrounding interstitial lipids. Folding, conformational equilibria, ligand binding, ion permeation, topography, and diffusion of the nAChR are modulated by membrane lipids. The knowledge gained from biophysical studies of this prototypic membrane protein can be applied to other neurotransmitter receptors and most other integral membrane proteins.

SUBMITTER: Barrantes FJ

PROVIDER: S-EPMC10808158 | biostudies-literature | 2023

REPOSITORIES: biostudies-literature

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Modulation of a rapid neurotransmitter receptor-ion channel by membrane lipids.

Barrantes Francisco J FJ

Frontiers in cell and developmental biology 20240111

Membrane lipids modulate the proteins embedded in the bilayer matrix by two non-exclusive mechanisms: direct or indirect. The latter comprise those effects mediated by the physicochemical state of the membrane bilayer, whereas direct modulation entails the more specific regulatory effects transduced via recognition sites on the target membrane protein. The nicotinic acetylcholine receptor (nAChR), the paradigm member of the pentameric ligand-gated ion channel (pLGIC) superfamily of rapid neurotr ...[more]

PMID: 38274273

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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.

Project description:Ivermectin is an anthelmintic drug that works by inhibiting neuronal activity and muscular contractility in arthropods and nematodes. It works by activating glutamate-gated chloride channels (GluClRs) at nanomolar concentrations. These receptors, found exclusively in invertebrates, belong to the pentameric Cys-loop receptor family of ligand-gated ion channels (LGICs). Higher (micromolar) concentrations of ivermectin also activate or modulate vertebrate Cys-loop receptors, including the excitatory nicotinic and the inhibitory GABA type-A and glycine receptors (GlyRs). An X-ray crystal structure of ivermectin complexed with the C. elegans ? GluClR demonstrated that ivermectin binds to the transmembrane domain in a cleft at the interface of adjacent subunits. It also identified three hydrogen bonds thought to attach ivermectin to its site. Site-directed mutagenesis and voltage-clamp electrophysiology have also been employed to probe the binding site for ivermectin in ?1 GlyRs. These have raised doubts as to whether the hydrogen bonds are essential for high ivermectin potency. Due to its lipophilic nature, it is likely that ivermectin accumulates in the membrane and binds reversibly (i.e., weakly) to its site. Several lines of evidence suggest that ivermectin opens the channel pore via a structural change distinct from that induced by the neurotransmitter agonist. Conformational changes occurring at locations distant from the pore can be probed using voltage-clamp fluorometry (VCF), a technique which involves quantitating agonist-induced fluorescence changes from environmentally sensitive fluorophores covalently attached to receptor domains of interest. This technique has demonstrated that ivermectin induces a global conformational change that propagates from the transmembrane domain to the neurotransmitter binding site, thus suggesting a mechanism by which ivermectin potentiates neurotransmitter-gated currents. Together, this information provides new insights into the mechanisms of action of this important drug.

Dataset Information

Modulation of a rapid neurotransmitter receptor-ion channel by membrane lipids.

Publications

Modulation of a rapid neurotransmitter receptor-ion channel by membrane lipids.

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