FliG is a core component of the bacterial flagellar motor switch complex (C-ring), which assembles together with FliM and FliN on the cytoplasmic face of the MS-ring (FliF) at the base of the flagellar basal body. FliG is a peripheral, cytoplasmic-side membrane protein organized into three domains: an N-terminal domain that docks onto the FliF MS-ring, a middle domain that binds FliM, and a C-terminal domain bearing the conserved "torque helix" that interacts electrostatically with the cytoplasmic loops of the MotA/MotB-type stator units. Through these stator contacts FliG couples ion-motive-force-driven stator activity to rotation of the rotor, making it the key element that transmits torque to the flagellum. FliG also mediates directional switching of flagellar rotation: as the output of the chemotaxis signaling pathway, phosphorylated CheY binds the C-ring (FliM/FliN) and triggers large conformational rearrangements in FliG that reorient its stator-facing surface, switching rotation between counterclockwise and clockwise states. The protein is therefore essential for both flagellum-dependent motility and the chemotactic control of swimming direction. In Pseudomonas putida KT2440 the gene (PP_4368) lies within the flagellar gene cluster and is co-transcribed in the fliEFG operon.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003774 cytoskeletal motor activity | IEA GO_REF:0000002 | MODIFY | Summary: FliG is a rotor/switch subunit that transmits torque generated by the assembled stator-rotor system, but it does not independently constitute a motor. Assigning the whole complex's cytoskeletal motor activity to FliG alone overstates the molecular function of this structural/mechanical subunit. Reason: FliG directly contributes to torque generation in the assembled flagellar motor, but GO:0140605 states the proton-motive-force-driven motor activity more precisely and should use contributes_to rather than enables for this rotor subunit. Proposed replacements: proton motive force-driven motor activity |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Localization annotation from the UniProt Subcellular Location mapping. FliG is a peripheral membrane protein on the cytoplasmic side of the inner (plasma) membrane, so this is not incorrect, but it is a generic location. The more specific and informative location for FliG is the flagellar basal body / C-ring (captured by GO:0009425 and GO:0009288). Reason: Accurate but non-specific; FliG associates with the cytoplasmic side of the inner membrane as part of the basal body. The basal body annotation is more informative and is the core localization. |
| GO:0006935 chemotaxis | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: FliG is the motor-switch output of the chemotaxis pathway: phosphorylated CheY binds the C-ring and FliG undergoes conformational changes that switch rotation direction, biasing the random-walk/run-tumble behavior. Involvement in chemotaxis is therefore well supported by conserved mechanism. This is a downstream/effector role (the actual flagellum-dependent motility and switching are the more proximal functions), so it is retained as a non-core biological process. Reason: FliG mediates the motor-switching output of chemotaxis (CheY-P -> C-ring -> FliG reorientation), but its core process is flagellar rotation/motility; chemotaxis is the higher-level process it serves. |
| GO:0009288 bacterial-type flagellum | IEA GO_REF:0000002 | ACCEPT | Summary: FliG is a structural component of the bacterial flagellum (the C-ring of the basal body). Correct cellular component annotation, consistent with family assignment and conserved architecture. Reason: FliG is a bona fide flagellar structural protein; accurate location. |
| GO:0009425 bacterial-type flagellum basal body | IEA GO_REF:0000044 | ACCEPT | Summary: FliG assembles into the C-ring (switch complex) on the cytoplasmic face of the MS-ring at the base of the basal body. This is the most specific and accurate localization for FliG and represents its core cellular component. Reason: Specific, accurate localization to the basal body C-ring; core component location. Supporting Evidence: file:PSEPK/fliG/fliG-deep-research-openscientist.md FliG is among the very first proteins added during basal-body assembly |
| GO:0071973 bacterial-type flagellum-dependent cell motility | IEA GO_REF:0000120 | ACCEPT | Summary: FliG is essential for flagellar rotation and hence for flagellum-dependent motility; it couples stator activity to torque generation in the rotor. This is a core biological process for the gene product, well supported by conserved FliG function. Reason: Flagellum-dependent motility is the primary biological process FliG enables, via torque transmission and rotation. Core process. |
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Download this section (compressed HTML)Q: Does deletion of fliG in P. putida KT2440 produce a non-motile (non-flagellated or paralyzed) phenotype, as predicted from conserved FliG function?
Q: Is FliG function in P. putida modulated by c-di-GMP effectors (e.g., FlgZ/PP4397) acting as a motor brake on the C-ring or stator?
Experiment: Construct an in-frame fliG deletion and complementation in P. putida KT2440 and assay swimming/swarming motility and flagellation by electron microscopy.
Experiment: Co-purification / bacterial two-hybrid assays to confirm FliG-FliF, FliG-FliM, and FliG-MotA interactions in P. putida.
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