Structure of the bacterial flagellar hook and implication for the molecular universal joint mechanism

Nature. 2004 Oct 28;431(7012):1062-8. doi: 10.1038/nature02997.


The bacterial flagellum is a motile organelle, and the flagellar hook is a short, highly curved tubular structure that connects the flagellar motor to the long filament acting as a helical propeller. The hook is made of about 120 copies of a single protein, FlgE, and its function as a nano-sized universal joint is essential for dynamic and efficient bacterial motility and taxis. It transmits the motor torque to the helical propeller over a wide range of its orientation for swimming and tumbling. Here we report a partial atomic model of the hook obtained by X-ray crystallography of FlgE31, a major proteolytic fragment of FlgE lacking unfolded terminal regions, and by electron cryomicroscopy and three-dimensional helical image reconstruction of the hook. The model reveals the intricate molecular interactions and a plausible switching mechanism for the hook to be flexible in bending but rigid against twisting for its universal joint function.

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / ultrastructure
  • Computer Simulation
  • Cryoelectron Microscopy
  • Crystallography, X-Ray
  • Models, Molecular
  • Peptide Fragments / chemistry
  • Peptide Fragments / ultrastructure
  • Pliability
  • Protein Structure, Quaternary
  • Protein Subunits / chemistry
  • Salmonella typhimurium / chemistry*


  • Bacterial Proteins
  • FlgE protein, Bacteria
  • Peptide Fragments
  • Protein Subunits

Associated data

  • PDB/1WLG