Extended Data Figure 3: Quality of the electron density maps.
a, Top view of a slab of the transmembrane domain, shown as ribbon (colour code as in Fig. 1c) with blue mesh representing the maximum-likelihood 2mFo−DFc electron density map contoured at a level of 1σ. b, Side view of one subunit of the 5-HT3 receptor as ribbon with the same density map. c, Enlarged views of the complementary subunit (top) (at the binding site level viewed from the principal subunit) and of the binding site (bottom). The main chain is represented as ribbon with side chains as sticks, and overlaid with the same density map. d, Enlarged view of the extracellular side of M4, which is not well defined in electron density maps (contoured at 1σ in blue and 1.5σ in yellow). e, Enlarged views of the intracellular post-M3 loop and MX helix (both green) and the triplet of arginines of MA (inset). Only Cα atoms of the MX helix were modelled. f, Stereo view of one subunit, similar to panel b.
