nano-sized rotary machines in bacteria tagged posts

1. Schematic diagram of the bacterial flagellar basal body with name and size of each part.
2. Molecular models of the flagellar rod (purple) and hook (blue green) and their comparison. (a) The model of the rod and hook complex including their direct connection in a section along their tubular axis. The structures of their corresponding domains are nearly identical. (b) Structural comparison of the rod and hook subunits by superposition. Domain D1 of the hook protein is more tilted than that of the rod protein by 7°, producing a gap between subunits in the axial neighbors to make the entire hook flexible in bending. (c) The C-terminal helix (blue) of the hook is shorter than that of the rod, making an axial gap between subunits in the hook structure but not in the rod.