Extended Data Figure 1: Quality of electron microscopy data.

a–j, Data collected on a FEI Titan Krios in 1 mM EGTA (a–e) and on a JEOL 3200 microscope in 10 mM CaCl₂ (f–j)_. a, f, Typical low dose cryo-EM micrographs of RyR1 vitrified in holey carbon grid recorded at an accelerating voltage of 300 kV (a) and 200 kV (f). b, g, Power spectra of the low dose micrographs. Thon rings are visible up to a resolution of 5 Å (b) and 10 Å (g). c, h, Representative two-dimensional class averages calculated in SPARX (c) and RELION (h) show characteristic views of RyR1. d, i, FSC curves between two independently refined half data sets (gold standard) shown for a set of all particles (solid black) and different conformational states (coloured curves). FSC between the volume calculated from all particles and the molecular model of RyR1 are shown as dotted black curves. FSC levels of 0.143 and 0.5 corresponding to the resolution cut off for density maps and the model are indicated. According to the 0.5 criterion the resolution of the model is 8.0 and 9.0 Å for the RyR1 reconstructions of closed and open states. The resolution is slightly lower than that of the map because of incompleteness of the model (the polyalanine model accounts for only about half of all the atoms of RyR1). e, j, Three-dimensional map of RyR1 coloured according to the local resolution calculated in ResMap from two unmasked volumes calculated from independently refined halves of the data sets. The resolution of the electron micoscropy map is heterogeneous with the highest resolution close to the centre of the molecule and the lowest resolution at the periphery. k, Statistics of single particle data.