Structure and Function of the Nicotinic Acetylcholine Receptor and of the Voltage-dependent Na⁺-Channel

Abstract

Nicotinic acetylcholine receptors (AChRs) from electric organs and muscle of different species have been shown to be highly conserved proteins composed of four homologous subunits occurring in the stoichiometry α₂βγδ and forming a pseudosymmetric pentameric complex (see Raftery et al. 1983). The availability of large quantities of AChR from Torpedo electric organ has greatly facilitated detailed studies of its structure and function. It has been demonstrated that the α₂βγδ complex constitutes the complete physiological receptor for postsynaptic depolarization by ACh and contains both the binding sites for cholinergic ligands and the cation gating unit (Moore and Raftery 1980; Wu et al. 1981). Each subunit spans the postsynaptic membrane and each has been shown to be exposed to the lipid bilayer suggesting that all subunits may interact with the surrounding membrane in a related fashion (see Raftery et al. 1983).