Cys-loop receptors

The Cys-loop ligand-gated ion channel superfamily is composed of nicotinic acetylcholine, GABAA, GABAA-ρ, glycine, 5-HT3, and zinc-activated (ZAC) receptors that are composed of five protein subunits that form a pentameric arrangement around a central pore. There are usually 2 alpha subunits and 3 other beta, gamma, or delta subunits (some consist of 5 alpha subunits). The name 'Cys-loop' is because this type of receptors possess a characteristic loop formed by 13 highly conserved amino acids between two cysteine (Cys) residues which form a disulfide bond, near the N-terminal extracellular domain. The Cys-loop ligand-gated ion channel superfamily is composed of nicotinic acetylcholine, GABAA, GABAA-ρ, glycine, 5-HT3, and zinc-activated (ZAC) receptors that are composed of five protein subunits that form a pentameric arrangement around a central pore. There are usually 2 alpha subunits and 3 other beta, gamma, or delta subunits (some consist of 5 alpha subunits). The name 'Cys-loop' is because this type of receptors possess a characteristic loop formed by 13 highly conserved amino acids between two cysteine (Cys) residues which form a disulfide bond, near the N-terminal extracellular domain. Cys-loop receptors are known only in eukaryotes, however they are part of a larger family of pentameric ligand-gated ion channels, which outside the Cys-loop clade are missing the pair of bridging cysteine residues. The larger superfamily includes bacterial (e.g. GLIC) as well as non-Cys-loop eukaryotic receptors, and is referred to as 'pentameric ligand-gated ion channels', or 'Pro-loop receptors'. All subunits consist of a conserved extracellular large N-terminal domain, three highly conserved transmembrane domains, a cytoplasmic loop of variable size and amino acid sequence, and a fourth transmembrane domain with a relatively short and variable extracellular C terminal.The neurotransmitters bind at the interface between subunits in the extracellular domain. Each subunit contains 4-membrane-spanning alpha helices (M1, M2, M3, M4). The pore is formed primarily by the M2 helices.