Polar confinement of a macromolecular machine by an SRP-type GTPase

Area of Science:

• Microbiology
• Cell Biology
• Molecular Biology

Background:

• The bacterial flagellum is a complex motility organelle.
• Its assembly initiates with the MS-ring (FliF) and C-ring (FliG, FliM, FliN) at the cell pole.
• The precise mechanism of polar targeting by the SRP-type GTPase FlhF remains elusive.

Purpose of the Study:

• To elucidate the mechanism by which FlhF directs flagellar protein assembly to the bacterial cell pole.
• To identify the molecular interactions involved in FlhF-mediated polar localization.
• To understand the regulatory role of FlhG in flagellar assembly.

Main Methods:

• Protein interaction studies to map FlhF binding partners.
• Analysis of flagellar protein localization in wild-type and mutant strains.
• Investigating the functional interplay between FlhF, HubP/FimV, FliF, FliG, FliM, FliN, and FlhG.

Main Results:

• FlhF anchors developing flagellar structures to the polar landmark protein HubP/FimV.
• The GTPase domain of FlhF interacts with HubP, while its N-terminal domain binds FliG.
• FlhF-bound FliG interacts with the MS-ring protein FliF, forming a FliF-FliG complex recruited to the pole.
• FlhG modulates FlhF activity, regulating FliG interaction with FliM-FliN and flagellar assembly progression.

Conclusions:

• FlhF acts as a crucial scaffold, linking flagellar basal body components to the cell pole via HubP/FimV.
• This interaction ensures the correct spatial organization and initiation of flagellar assembly.
• FlhG provides regulatory control over flagellar assembly progression at the cell pole.