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Updated: May 11, 2026

Biophysical Characterization of Flagellar Motor Functions
Published on: January 18, 2017
Energy source of flagellar type III secretion
Koushik Paul1, Marc Erhardt, Takanori Hirano
1Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, Utah 84112, USA.
Bacterial flagella use a proton motive force (PMF) for protein secretion, not ATP hydrolysis. This finding redefines the energy source for type III secretion systems in Salmonella.
Area of Science:
- Microbiology
- Molecular Biology
- Cellular Biology
Background:
- Bacterial flagella utilize a specialized type III secretion system to export proteins for filament assembly.
- This system shares similarities with injectisomes used by pathogens to deliver effector proteins into host cells.
- The flagellar secretion apparatus was previously thought to be powered by the ATPase FliI.
Purpose of the Study:
- To investigate the energy source driving protein export in the bacterial flagellar type III secretion system.
- To determine the role of ATP hydrolysis by FliI in flagellar secretion.
- To elucidate the mechanism of protein translocation across the bacterial membrane.
Main Methods:
- Utilizing the protonophore CCCP to disrupt the proton motive force (PMF).
- Assessing flagellar export substrate translocation under disrupted PMF conditions.
- Analyzing cellular ATP levels and motility in flagellar secretion mutants lacking FliI and other ATPases.
Main Results:
- Proton motive force (PMF) is essential for flagellar protein secretion.
- Inhibition of PMF with CCCP halted substrate export without reducing cellular ATP.
- Mutants lacking FliI and other type III secretion ATPases exhibited impaired motility and flagella formation.
- ATP hydrolysis by FliI is not required for type III secretion in flagella.
Conclusions:
- The flagellar secretion apparatus functions as a proton-driven protein exporter.
- ATP hydrolysis is not essential for type III secretion in bacterial flagella.
- This study redefines the energy requirements for flagellar assembly and type III secretion.
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