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 contributes to the proton-driven flagellar motor through the assembled rotor. Reason: Current QuickGO places GO:0140605 below GO:0003774 through is_a/part_of ancestry, and the GO:0003774 definition explicitly includes electrochemical-gradient-driven flagellar rotation. The more specific proton-motive-force-driven motor term describes the assembled motor to which FliG contributes the stator-facing rotor interface. FliG does not by itself conduct protons or generate an autonomous motor. Comparative torque-interface residues are source-specific mechanistic evidence; no unverified KT2440 residue numbering is assigned. Proposed replacements: proton motive force-driven motor activity Supporting Evidence: PMID:31452860 FliG is directly involved in torque generation [8]. PMID:31452860 Highly conserved Arg-281 and Asp-289 residues are located on the torque helix of FliG (HelixTorque) [11] and interact with Glu-98 and Arg-90 of MotAC |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | MODIFY | Summary: FliG is not an integral membrane protein; it is a peripheral protein attached to the cytoplasmic face of the MS ring (FliF) in the inner membrane, as the curated UniRule (PIRNR) location states. Reason: Correct but general. The supported location is GO:0009898 cytoplasmic side of plasma membrane (a part_of descendant of plasma membrane), consistent with the treatment of peripheral cytoplasmic-face chemotaxis/motor proteins in the E. coli reviews. The core location is the C ring (see the basal body rows). Proposed replacements: cytoplasmic side of plasma membrane Supporting Evidence: file:PSEPK/fliG/fliG-uniprot.txt Cell inner membrane; Peripheral membrane protein; Cytoplasmic side |
| GO:0006935 chemotaxis | IEA GO_REF:0000002 | ACCEPT | Summary: FliG relays switch conformational changes to the stator-facing rotor interface during chemotaxis. Reason: Direction switching is part of FliG’s central rotor function, not a peripheral phenotype. The mechanistic assignment is inferred from the conserved FliG switch architecture and comparative bacterial motor studies; no KT2440 purified switch assay is asserted. The comparative review explicitly links CheY-P control through FliM/FliN to FliG rotor reorientation; this establishes a mechanistic bridge to guided movement rather than switching in isolation. Domain/residue notation is that of the comparative source, not a mapped KT2440 residue experiment. Supporting Evidence: PMID:31452860 The binding of CheY-P to FliM and FliN affects subunit-subunit interactions between FliMM domains and between FliMC and FliN in the C ring to induce a 180° rotation of FliGCC relative to MotAC, thereby allowing the motor to rotate in CW direction |
| GO:0009288 bacterial-type flagellum | IEA GO_REF:0000002 | MODIFY | Summary: FliG is a component of the flagellum, specifically of the C ring at the cytoplasmic base of the basal body. Reason: Correct but general. The specific supported location is GO:0009433 bacterial-type flagellum basal body, C ring, which is part_of the flagellum; FliG is one of the three C-ring switch proteins. Proposed replacements: bacterial-type flagellum basal body, C ring Supporting Evidence: file:PSEPK/fliG/fliG-uniprot.txt FUNCTION: FliG is one of three proteins (FliG, FliN, FliM) that forms the rotor-mounted switch complex (C ring), located at the base of the basal body. PMID:31452860 the FliM1/FliN3 complex binds to the FliG ring structure through a one-to-one interaction between FliG and FliM to form the continuous C ring wall |
| GO:0009425 bacterial-type flagellum basal body | IEA GO_REF:0000044 | MODIFY | Summary: FliG assembles into the C ring (switch complex) on the cytoplasmic face of the MS ring at the base of the basal body. Reason: Correct but general. The C ring is a substructure of the basal body (GO:0009433 part_of GO:0009425), and the curated FliG family function places FliG in the C ring together with FliM and FliN. Proposed replacements: bacterial-type flagellum basal body, C ring Supporting Evidence: file:PSEPK/fliG/fliG-uniprot.txt FUNCTION: FliG is one of three proteins (FliG, FliN, FliM) that forms the rotor-mounted switch complex (C ring), located at the base of the basal body. 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 required for flagellar rotation and hence for flagellum-dependent motility; it couples stator activity to rotation of the rotor. Reason: Core process: FliG performs a step of motility (torque transmission at the rotor-stator interface). The protein carries the conserved FliG N, M and C domains (NCBIfam TIGR00207) and the gene lies in the KT2440 flagellar cluster. Supporting Evidence: PMID:31452860 FliG is directly involved in torque generation [8]. file:PSEPK/fliG/fliG-uniprot.txt DR NCBIfam; TIGR00207; fliG; 1. file:PSEPK/fliG/fliG-deep-research-falcon.md In *P. putida* KT2440, strand-specific RNA-seq shows a continuous transcription unit annotated as **fliEFG**, indicating that **fliE–fliF–fliG** are co-transcribed as an operon within the flagellar gene cluster |
| GO:0005198 structural molecule activity | IC PMID:31452860 Directional Switching Mechanism of the Bacterial Flagellar M... | NEW | Summary: Proposed molecular function. FliG forms the ring onto which FliM/FliN complexes bind one-to-one to build the continuous C-ring wall, and its N-terminal domain docks the ring onto the MS ring. Reason: FliG contributes to the structural integrity of the C ring ("structural molecule activity: contributes to the structural integrity of a complex"), which is the module-level activity of the C ring. Inferred from the conserved FliG domain architecture (Pfam FliG_N, FliG_M, FliG_C) and structural studies of FliG in other bacteria; no KT2440 biochemical data exist, hence IC. Supporting Evidence: PMID:31452860 the FliM1/FliN3 complex binds to the FliG ring structure through a one-to-one interaction between FliG and FliM to form the continuous C ring wall PMID:31452860 FliG consists of FliGN, FliGM and FliGC domains and two helix linkers, HelixNM and HelixMC. |
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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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