Supplementary Figure 2: Image processing of tilted dataset leading to a 3.6 Å resolution cryo-EM reconstruction.

a, Representative cryo-EM image collected with a 40° tilt showing well-defined, monodispersed particles (scale bar represents 100 nm). b, Angular distribution of particles from the tilted dataset is cone-like, corresponding to a majority of top-views. c, A single, well-defined reconstruction was produced using cryoSPARC and subsequently refined to high resolution using RELION-3.0 (see Methods for details). d, Reference-free 2D classes of the tilted data reveal secondary structure features. e, The secondary structure features are consistent with the estimated resolution of the map, with well-defined secondary structure and distinctive densities for large side-chain. f, The overall resolution (based on the Fourier shell correlation (FSC) 0.143 criterion) for the symmetrized reconstruction is 3.5 Å (3.6 Å if using randomized phases), and 3.9 Å for the unsymmetrized reconstruction. The map versus model resolution is 3.7 and 4 Å, respectively, for the symmetrized and unsymmetrized maps. g, 3D map for the C2 (symmetrized, left) and C1 (unsymmetrized, right) reconstructions colored by local resolution showing the core of the structure to be around 3.5 Å. To show some of the most disordered regions, the C1 map is shown low-pass filtered to both 4 Å and 6 Å.