Supplementary Figure 3: Cryo-EM data processing.

a, Two (left and middle panel) and one (right) representative micrographs from data collection of SegA and SegB A315E, respectively. For each structure, a representative particle and its computed diffraction pattern are shown in the inset. The white line in each particle image indicates the direction of the fibril axis. The 4.8 Å reflection in the diffraction pattern corresponds to the helical rise. b, (left) Representative 2D class averages, (middle) computed diffraction pattern from 2D class, and (right) central slice from the final reconstruction of each structure. c, d, FSC curves between two half-maps (c) and the cryo-EM reconstruction and refined atomic model (d) for each structure, using the same color coding as in (a) and (b). e, Comparison of 2D class average (left) and projection of 3D reconstruction from the same orientation of SegA-slow, when using C2 (middle) or pseudo-2₁ (right) symmetry for reconstruction. f, Manually assembled full pitch of SegA-slow from 2D class averages and its computed diffraction pattern with the 4.8 Å region enlarged confirms the presence of C_n rotational symmetry due to a reflection at n = 0.