Figure 1:

Nicotinic acetylcholine receptor subunit assemblies and sequence diversity. (A) Subunit arrangement of the muscle-type nicotinic receptor. Orthosteric binding sites are denoted by arrows at α1-γ/ε and α1-δ interfaces. (B) Subunit arrangement of a homomeric neuronal nicotinic receptor, α7. α9 can also form homomers. (C) Subunit arrangement of heteromeric neuronal nicotinic receptors. αX positions can be occupied by α2, α3, α4, or α6 subunits, βY positions can be occupied by β2 or β4 subunits, and the last position (αZ/βZ) can be occupied by any of the above as well as α5 and β3. (D) Sequence identity matrix of all human nicotinic receptor subunits. α8 is not found in mammals and is not included. Principal α subunits are indicated in green, complementary β subunits in blue, complementary muscle-type subunits in yellow and orange, and auxiliary subunits in teal. Highlighted boxes show sequence identities between interchangeable subunits.