Energy source of flagellar type III secretion

Nature. 2008 Jan 24;451(7177):489-92. doi: 10.1038/nature06497.


Bacterial flagella contain a specialized secretion apparatus that functions to deliver the protein subunits that form the filament and other structures to outside the membrane. This apparatus is related to the injectisome used by many gram-negative pathogens and symbionts to transfer effector proteins into host cells; in both systems this export mechanism is termed 'type III' secretion. The flagellar secretion apparatus comprises a membrane-embedded complex of about five proteins, and soluble factors, which include export-dedicated chaperones and an ATPase, FliI, that was thought to provide the energy for export. Here we show that flagellar secretion in Salmonella enterica requires the proton motive force (PMF) and does not require ATP hydrolysis by FliI. The export of several flagellar export substrates was prevented by treatment with the protonophore CCCP, with no accompanying decrease in cellular ATP levels. Weak swarming motility and rare flagella were observed in a mutant deleted for FliI and for the non-flagellar type-III secretion ATPases InvJ and SsaN. These findings show that the flagellar secretion apparatus functions as a proton-driven protein exporter and that ATP hydrolysis is not essential for type III secretion.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Antigens, Bacterial / genetics
  • Antigens, Bacterial / metabolism
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Carbonyl Cyanide m-Chlorophenyl Hydrazone / pharmacology
  • Energy Metabolism* / drug effects
  • Flagella / chemistry
  • Flagella / metabolism*
  • Hydrogen-Ion Concentration
  • Mutation / genetics
  • Protein Transport / drug effects
  • Protein Transport / genetics
  • Proton-Motive Force / drug effects
  • Proton-Motive Force / physiology*
  • Proton-Translocating ATPases / metabolism
  • Salmonella enterica / enzymology
  • Salmonella enterica / genetics
  • Salmonella enterica / metabolism*


  • Antigens, Bacterial
  • Bacterial Proteins
  • FlgE protein, Bacteria
  • invJ protein, Salmonella typhimurium
  • fliH protein, Bacteria
  • fliI protein, bacteria
  • FlgM protein, Bacteria
  • Carbonyl Cyanide m-Chlorophenyl Hydrazone
  • Adenosine Triphosphate
  • Proton-Translocating ATPases