Fig. 1: Structure of the type 1 pilus during FimD-catalyzed assembly of FimA.
a Schematic overview of type 1 pilus biogenesis and assembly termination by FimI. All pilus subunits are transported through the inner membrane by the SecYEG translocon and fold in the periplasm once bound to the chaperone FimC. Only folded, FimC-bound subunits are assembly competent. FimI is incorporated as the last pilus subunit and terminates pilus assembly. b Schematic representation of the domain organization of all type 1 pilus components. c Cryo-EM map (composite of map II (pilus rod) and map III (assembly platform)) of the FimA-bound usher FimD in the process of pilus assembly. Cryo-EM density is colored based on the respective models II and III. d Angle and interface (inset) between subunit FimAn and FimAn-1 in model IV. FimAn (navy blue) and FimAn-1 (pink) are both shown as cartoon representations and map IV is shown in the background. Central axes of the two subunits are shown as black lines. e Angle and interface (inset) between subunit FimAn-1 and FimAn-2 in model V. FimAn-1 (pink) and FimAn-2 (dark blue) are both shown as cartoon representations and map V is shown in the background. Central axes of the two subunits are shown as black lines. The insets in (d) and (e) show that there are only few potential hydrogen bonds stabilizing the FimAn-FimAn-1 and FimAn-1-FimAn-2 interfaces. The limited resolution in this area does not allow precise modeling of side chain conformations. f Angle and interface between subunit FimAn-2 and FimAn-3 in model II. FimAn-2 (dark blue) and FimAn-3 (blue green) are shown as cartoon representations and map II and III are shown in the background. Central axes of the two subunits are shown as black lines. The inset shows the hydrogen bonds that can be potentially formed by residues at the interface between FimAn-2 (dark blue), the Nte of FimAn-1 (pink) and FimAn-3 (blue green).
