Fig. 2.

Structure and topology of cys-loop ligand-gated ion channels. A. The schematic representation of topography of the receptor showing N-terminal extracellular domain, intracellular domain, four membrane spanning transmembrane cylindrical domains, cys-loop having cysteine residues participating in disulfide formation. B. Top view of a pentameric ion-channel showing transmembrane helical arrangement of each subunit showing the location of TM2 lining the pore. C. Schematic of a generic cys-loop LGIC showing the arrangement of subunits to form a central ion pore. The notional orthosteric- and allosteric-ligand binding site are indicated in the extracellular and transmembrane domains.