Regulation of flagellation patterns by FlhF and FlhG: analysis of interaction networks in Shewanella putrefaciens and Bacillus subtilis
Year: 2025
Type: dissertation
Abstract: Flagella are organelles of locomotion that allow bacteria to respond to changes in the environment by moving toward an attractant or away from repellents. The flagellum is a complex machinery with a conserved architecture. Intracellularly, the basal body consists of the stator and rotor complex, which generates the rotation/torque, and a type 3 flagellar secretion system, which is required for the export of extracellular proteins. The peptidoglycan layer and the outer membrane are spanned by the rod, which transmits the rotation to the extracellular hook. Finally, the hook transmits the rotation to the filament and the cell moves. Unlike the architecture, the distribution pattern of flagella is species-specific. Localization can be restricted to the pole or lateral sides of the cell, and the number can vary from one to nearly 100. These patterns must undergo several regulatory mechanisms to be maintained through the generations. In several species, the proteins FlhF and FlhG have been implicated in the regulation of the flagellar pattern. FlhF belongs to the group of SRP-GTPases and forms a GTP-dependent homodimer with the conserved NG domain. The other protein, FlhG, is a MinD-like ATPase and is located downstream of the flhf gene. When ATP is bound, the proteins form a homodimer and are able to bind to the membrane. FlhG has an additional activator helix at its N-terminus, which can bind FlhF and stimulate GTPase activity. In polar flagellated bacteria such as Shewanella putrefaciens, FlhF is required for correct localization of the flagellum, whereas FlhG regulates the number of flagella. In the peritrichously flagellated bacterium Bacillus subtilis, both proteins are required for proper distribution: FlhG maintains a minimum distance between the flagella and FlhF keeps the distribution in an organized pattern and away from the poles. However, the mechanism behind this regulation is not fully understood. This work presents a biochemical and structural characterization of the SRP-GTPase FlhF of the monotrichiously flagellated bacterium S. putrefaciens. The structure of the GDP-bound form of the NG-domain compared to the GTP-bound form provides insight into structural conformational changes upon nucleotide binding and may explain the different targets compared to the other SRP-GTPases FtsY and Ffh. The structure of the previously uncharacterized B-domain of FlhF was also solved and shows an interaction with the C-ring protein FliG. This interaction indicates that FlhF is involved in the hierarchical assembly of the MS- and C-rings of the flagellar basal body. The simultaneous interaction of FliG and the landmark protein HubP with FlhF could suggest a "diffusion and capture" mechanism by which the first flagellar protein FliF is captured by FlhF-bound FliG, which is recruited to the pole by HubP. This mechanism restricts the assembly of the flagellum to the cell pole and prevents premature C-ring assembly. In the peritrichous flagellated B. subtilis, the regulation is different. There, the cell cycle regulator GpsB was identified as a novel interaction partner of FlhG that phenocopies the deletion of flhG and couples cell wall elongation with flagella biosynthesis.
DOI: 10.17192/z2024.0483
Author: Dornes, Anita (Dr.)
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W6925416754
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