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transmembrane domain of Cys-loop neurotransmitter-gated ion channels This superfamily contains the transmembrane domain of Cys-loop neurotransmitter-gated ion channels, which include nicotinic acetylcholine receptor (nAChR), serotonin 5-hydroxytryptamine receptor (5-HT3), type-A gamma-aminobutyric acid receptor (GABAAR), and glycine receptor (GlyR). These ligand-gated ion channels (LGICs) are found across metazoans and have close homologs in bacteria. They are vital for communication throughout the nervous system where the sign of synaptic connections (excitatory or inhibitory) is determined by the charge of the ions that flow through these channels. In general, channels that conduct positive ions are excitatory, whereas channels that conduct negative ions are inhibitory. The transmembrane region consists of four transmembrane-spanning alpha-helical segments (M1-M4) that are linked by loops. The intracellular loop that links M1 and M2 determines the ion selectivity of the channel. GABAAR and GlyR are anionic channels, both mediating fast inhibitory synaptic transmission. Cl- ions are selectively conducted through the GABAAR receptor pore, resulting in hyperpolarization of the neuron. nAChR is a non-selective cation channel that is permeable to Na+ and K+, and some subunit combinations are also permeable to Ca2+. Na+ enters and K+ exits to allow net flow of positively charged ions inward. 5-HT3, a cation-selective channel, binds serotonin and is permeable to Na+, K+, and Ca2+. It mediates neuronal depolarization and excitation within the central and peripheral nervous systems. These ligand-gated chloride channels are critical not only for maintaining appropriate neuronal activity, but have long been important therapeutic targets: benzodiazepines, barbiturates, some intravenous and volatile anaesthetics, alcohol, strychnine, picrotoxin, and ivermectin all derive their biological activity from acting on the inhibitory half of the Cys-loop receptor family. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",