ETEC adhesion pili are helical filaments with approximately three subunits per turn, and 8- to 9-nm diameters. Representative cryo-EM images of CS17 pili are shown for each pilus type (left). Thousands of these images were used to compute three-dimensional helical reconstructions (center). Atomic models were fitted into the maps, with a single subunit shown in the same orientation as the map for each pilus type (top right). Models including three subunits are shown rotated 90 degrees (bottom right). While each pilus includes a beta-strand that fits into a hydrophobic groove in the preceding subunit, CS20 pilin subunits also include a staple that extends beyond the groove and contacts pilins four and five subunits away. Scale bar for all micrographs, 50 nm. CFA/I, CS17, CS20 PDB:8EHR,8EHS, and 8EHT, respectively.
