& Buhr, 1997; Li et al., 2006; Bali & Akabas,2004; Hosie et al., 2006). Each subunit consists of a long N-terminal extracellular hydrophilic region, followed by four trans-membrane (M) α-helices with a large intracellular loop between M3 and M4, and ends with a relatively short extracellular C-terminal domain, and M2 forms the lining of the ion channel. The structure of the Cys-loop pentameric LGIC superfamily has been resolved (currently 4 Å) for the nicotinic acetylcholine receptor of Torpedo marmorata obtained by cryo-electron microscopy and image reconstruction (Unwin, 2005). This has been combined with X-ray crystallography data on the homologous snail soluble acetylcholine binding protein (AChBP; Brejc et al., 2001), recently followed by that of the water soluble portion of the muscle nicotinic acetylcholine receptor (Dellisanti et al., 2007), and that of a related bacterial membrane LGIC receptor (Hilf & Dutzler, 2008).
