| Category | Key points | Best supporting citations (pqac ids) | URL/date |
|---|---|---|---|
| Identity | **UniProt Q88ET5 = FliG / PP_4368 in *Pseudomonas putida* KT2440**; annotated as the **flagellar motor switch protein FliG**. In KT2440, **fliE-fliF-fliG are co-transcribed** as the **fliEFG operon**, supporting assignment to the conserved flagellar motor/switch module rather than an unrelated protein family. | (pqac-00000013, pqac-00000012) | Leal-Morales et al., *Environmental Microbiology* (2022-12), https://doi.org/10.1111/1462-2920.15857 |
| Domains | FliG is a conserved **C-ring rotor/switch protein** with **N-, middle-, and C-terminal domains**. The **N-terminus binds FliF/MS-ring**, the **middle domain binds FliM**, and the **C-terminal region contains the torque helix** involved in stator coupling and switching. This matches the UniProt domain architecture for Q88ET5 (FliG family; FliG_N, FliG_M, FliG_C / motor-switch domains). | (pqac-00000020, pqac-00000008) | Minamino et al., *Computational and Structural Biotechnology Journal* (2019-07), https://doi.org/10.1016/j.csbj.2019.07.020; Bouteiller et al., *IJMS* (2021-03), https://doi.org/10.3390/ijms22073337 |
| Localization | FliG is **cytoplasmic and membrane-proximal**, forming the **cytoplasmic C-ring on the inner face of the MS-ring** at the base of the polar flagellum. Function is therefore at the **cell pole / basal body rotor**, not in the periplasm or extracellular space. | (pqac-00000019, pqac-00000008) | Minamino et al., *CSBJ* (2019-07), https://doi.org/10.1016/j.csbj.2019.07.020; Bouteiller et al., *IJMS* (2021-03), https://doi.org/10.3390/ijms22073337 |
| Complex membership | FliG is a core component of the **flagellar C-ring / switch complex** together with **FliM and FliN**, functionally linked to **FliF (MS-ring)** and the **MotA/MotB-type stator**. In pseudomonads, this places PP_4368 in the **flagellar motor and chemotaxis output pathway**. | (pqac-00000019, pqac-00000020, pqac-00000000) | Minamino et al., *CSBJ* (2019-07), https://doi.org/10.1016/j.csbj.2019.07.020; Wirebrand et al., *Scientific Reports* (2018-08), https://doi.org/10.1038/s41598-018-29785-w |
| Key interactions | Conserved interactions inferred from structure/function: **FliG–FliF** (assembly of rotor/MS interface), **FliG–FliM** (C-ring architecture and switching), and **FliG–MotA** electrostatic coupling for torque generation. In polar-flagellated bacteria, **FlhF can bind FliG** during early polar flagellum assembly; this was demonstrated in *Shewanella* and discussed as relevant to *P. putida* polar flagellation. c-di-GMP motor-brake proteins (YcgR/FlgZ-like systems) can target FliG-containing motors. | (pqac-00000020, pqac-00000003, pqac-00000011, pqac-00000000) | Johnson et al., *Nature Microbiology* (2024-03), https://doi.org/10.1038/s41564-024-01630-z; Arroyo-Pérez et al., *eLife* (2024-12), https://doi.org/10.7554/eLife.93004.3; Wirebrand et al., *Scientific Reports* (2018-08), https://doi.org/10.1038/s41598-018-29785-w |
| Regulation/operon | In KT2440, **fliEFG** is a defined transcriptional unit; RNA-seq/RT-PCR support an **operon boundary at the fliG-fliH intergenic region**. The broader flagellar cluster is controlled by a **FleQ/σ54-centered hierarchy** in *P. putida*, so fliG belongs to the **flagellar biogenesis regulon** even though these excerpts do not assign a dedicated promoter directly upstream of fliG alone. | (pqac-00000013, pqac-00000012, pqac-00000010, pqac-00000009) | Leal-Morales et al., *Environmental Microbiology* (2022-12), https://doi.org/10.1111/1462-2920.15857; Jiménez-Fernández et al., *PLOS ONE* (2016-09-16), https://doi.org/10.1371/journal.pone.0163142 |
| Recent structural insights (2023-2024) | 2023–2024 cryo-EM studies strongly refine FliG annotation: **FliG N- and C-terminal domains undergo ~180° movements between CCW and CW states**, and the **stator docking position shifts from the outside to the inside of the C-ring** across switching states. These data support FliG as the key **bidirectional gear/torque-transmission element** of the rotor. | (pqac-00000003, pqac-00000001, pqac-00000021) | Johnson et al., *Nature Microbiology* (2024-03), https://doi.org/10.1038/s41564-024-01630-z; Singh et al., *Nature Microbiology* (2024-04), https://doi.org/10.1038/s41564-024-01674-1 |
| Quantitative data | Recent quantitative work on the switch complex supports **~34 FliG molecules per C-ring** as a reference stoichiometry in enteric model systems; FliM averages were **45 (CW)** and **58 (CCW)**, indicating adaptive remodeling occurs mainly in FliM/FliN while FliG is comparatively stable. Review sources also summarize older approximate counts of **~25 FliG, 34 FliM, ~110 FliN**, but newer work favors **34 FliG** as the better current estimate. These numbers are not *P. putida*-specific but inform annotation of the conserved FliG family. | (pqac-00000016, pqac-00000017, pqac-00000008) | Tao et al., *mBio* (2023-03-22), https://doi.org/10.1128/mbio.00189-23; Bouteiller et al., *IJMS* (2021-03), https://doi.org/10.3390/ijms22073337 |


*Table: This table summarizes the most relevant functional annotation points for *Pseudomonas putida* KT2440 FliG (UniProt Q88ET5; PP_4368), including identity verification, localization, operon context, conserved interactions, and 2023–2024 structural insights. It is useful as a compact evidence map linking species-specific transcriptional data with broader mechanistic knowledge of FliG.*