Zouridakis_2014_Nat.Struct.Mol.Biol_21_976

We determined the X-ray crystal structures of the extracellular domain (ECD) of the monomeric state of human neuronal alpha9 nicotinic acetylcholine receptor (nAChR) and of its complexes with the antagonists methyllycaconitine and alpha-bungarotoxin at resolutions of 1.8 A, 1.7 A and 2.7 A, respectively. The structure of the monomeric alpha9 ECD superimposed well with the structures of homologous proteins in pentameric assemblies, denoting native folding, despite the absence of a complementary subunit and transmembrane domain. The interaction motifs of both antagonists were similar to those in the complexes with homologous pentameric proteins, thus highlighting the major contribution of the principal side of alpha9 ECD to their binding. The structures revealed a functionally important beta7-beta10 strand interaction in alpha9-containing nAChRs, involving their unique Thr147, a hydration pocket similar to that of mouse alpha1 ECD and a membrane-facing network coordinated by the invariant Arg210.