Module 3: Figure nicotinic acetylcholine receptor
Structural organization of the nicotinic acetylcholine receptor.
The nicotinic acetylcholine receptor (nAChR) is a typical cysteine-loop receptor. It is a pentamer that contains at least two α subunits together with different combinations of the other subunits. A cross section of the channel taken at the level of the membrane reveals that each subunit is made of four membrane-spanning segments (M1–M4), with M2 facing the pore (P). The organization of two subunits in longitudinal section (shown at the bottom) illustrates the way in which the M2 segment forms the pore. The N-terminal region that extends to the outside contains the cysteine loop. The way in which the acetylcholine binds may act to induce a movement of the M2 segments to open the pore (Module 3: Figure nicotinic acetylcholine receptor gating).