Fig. 4: Cryo-EM structures of PAM4 fibrils show a diversity of folds.

a Slices through the cryo-EM map of each PAM4 fibril structure, made by averaging the central 6x slices of the post-processed, sharpened map to display approximately a single helical layer. Scale bar = 3 nm. b Cryo-EM maps (grey, transparent surface) with fitted atomic models for each solved structure, displayed in the same order as in a. Each peptide chain is coloured blue-to-red from N- to C-terminus and a single helical layer is shown. c PAM4 structures represented as cartoon loops, coloured by subunit fold as indicated in d and with the N-terminal acetyl-Val or Fmoc-Val and C-terminal amide-His residues shown as sticks and labelled. Structures are displayed in the same order as in a. d Schematic representation of individual residues for the distinct monomeric conformations adopted by PAM4 and identified by cryo-EM. e Close-up views of the minimal repeating unit in each structure, displayed with cartoon backbone and stick side chains coloured by subunit as in c. Inter-protofilament steric zipper interactions are highlighted with shaded backgrounds, with arrows indicating the location of the GS-bend formed by Gly355 and Ser356. The insert highlights the formation of an intramolecular salt bridge between Lys353 and Asp358 that further stabilises the monomeric PAM4 FoldC.