Extended Data Figure 5: Cryo-EM density map of RyR1 at 6.1 Å resolution.

a–f, Backbone of the model in ribbon representation coloured as in Fig. 1 and cryo-EM density map from different regions of the structure are shown. a, Transmembrane region showing the inner helix and the helices of the voltage-sensor-like domain. The cytoplasmic part of the inner helix (in red) is resolved as good as the transmembrane helices indicating that the resolution inside the lipid nanodisc is similar to the nearby cytoplasmic regions. b, Pore helix and pore loops showing the absence of the second pore helix found in structurally homologous Na_v channels. c, d, Helices of α-solenoid domains 1 (c) and 2 (d). e, Fit of the SPRY2 domain in the density. f, One of the least resolved domains, repeat 1–2, rod-shaped densities corresponding to α-helices are visible. g, Structure and density maps of individual domains. Segments of the 6.1 Å RyR1 density map corresponding to individual domains of RyR1 are shown together with the ribbon models of the domains in rainbow colouring from the N terminus (blue) to the C terminus (red). The excellent fitting of the crystallographic model of the N-terminal AB domain (residues 12–532)¹¹ into the density, even revealing conformation of loops that were disordered in the crystal structure, indicates the high quality of our electron microscopy map. The density segment for FKBP bound to RyR1 was extracted from the 8.5 Å cryo-EM map of RyR1 in its open state.