a, A representative motion-corrected micrograph showing the distribution of Orco–Fab single particles (three particles are circled). Scale bar, 50 nm. b, 2D averages of classes selected for further processing. c, Initial density map from 3D refinement in RELION using all of the particles in b with C4 symmetry imposed. d, Soft mask and final density map after refinement in Frealign. e, Fourier shell correlation (FSC) curves for the final cryo-EM density maps. The horizontal dashed line represents the 0.143 cutoff value. f, Orientation distribution of the particles included in the final 3D map of the Orco–Fab complex in d (as reported by RELION). g, Approximate local resolution of the entire Orco–Fab density map (left) and only Orco (right). h, Cryo-EM densities for the modelled regions are shown as grey mesh. Orco models are drawn as sticks with carbon atoms coloured according to Fig. 2, and oxygen, nitrogen and sulfur atoms coloured red, blue and yellow, respectively.