Cys-loop receptors

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The Cys-loop ligand-gated ion channel superfamily is composed of nicotinic acetylcholine, GABAA, GABAA, glycine and 5-HT3 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). Cys-loop receptors possess a characteristic loop formed by a disulfide bond between two cysteine (Cys) residues 13 highly conserved amino acids apart near the N-terminal extracellular domain of the alpha subunit.

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. All alpha subunits have a characteristic cys-cys pair in the N-terminal extracellular domain, this is shown to be essential for agonist binding. 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 M2 of the two alpha subunits.

The M3-M4 linker is the intracellular domain that binds the cytoskeleton.

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