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Figure 1
Structure of the ACh receptor in Torpedo postsynaptic membrane. (a) Micrographs of the tubular vesicles analysed in this study. The scale bar represents 500 Å. (b) Arrangement of subunits and TM helices in receptor dimers, forming the helical asymmetric unit. (c) The 5.8 Å density map and superimposed 2.7 Å structure of the Torpedo receptor (PDB entry 6uwz) obtained from detergent-solubilized protein complexed with α-bungarotoxin. MX helices are shown in red. (d) A sectional view through the map and superimposed model, showing details of the central transmembrane pore (functionally important amino acid residues on the α-subunit pore-lining M2 helices, 9′Leu, uppermost, and −1′Glu, are shown in red). (e) Part of the δ subunit involved in dimer formation, showing mismatch with the model (δ–δ disulfide bridge-forming cysteine shown in red). The C-terminal portion of δ, beyond M4, is not seen in the density map and is probably flexible (accounting for the variable configurations of isolated dimers; Rahman et al., 2020BB36).

IUCrJ
Volume 7| Part 5| September 2020| Pages 852-859
ISSN: 2052-2525
https://doi.org/10.1107/S2052252520009446