The “cys-loop” LGICs are pentameric proteins characterized by an obligatory cysteine double bond in the N-terminal binding domain. Each subunit protein contains an extracellular ligand-binding domain, four membrane spanning domains, and one large intracellular loop domain that also serves as a “portal” for ion permeability. This receptor class includes proteins with cation-permeable pores, the nicotinic acetylcholine (nAChR) and serotonin3 (5-HT3) receptors, as well as those with anion-permeable pores, the γ-aminobutyric acidA (GABAA), and strychnine-sensitive glycine (GlyR) receptors. This class of receptors is distributed throughout the peripheral and central nervous systems.
