Unwin_2002_Novartis.Found.Symp_245_5

The structure of the acetylcholine-gated channel, trapped in open as well as closed states, has been analysed by electron crystallographic methods. The channel has large vestibules extending from the membrane which shape the acetylcholine-binding pockets and facilitate selective transport of cations across a narrow membrane-spanning pore. When acetylcholine enters these pockets it triggers a concerted conformational change that opens the pore by destabilizing a gate in the middle of the membrane made by a ring of pore-lining alpha-helical segments. The alternative 'open' configuration of porelining segments reshapes the lumen and creates new surfaces, allowing the ions to pass through. Recent results, at nearly 4A resolution, have defined more precisely the structure of the pore and the design of the vestibular entrances.