FliN (PP_4357) is the small flagellar motor switch protein of the C ring of the polar flagella of Pseudomonas putida KT2440. It consists of a disordered N-terminal region and a C-terminal FliN/SpoA domain and belongs to the FliN/MopA/SpaO family (TIGR02480). By homology with the E. coli and Salmonella motors, three FliN subunits associate with the C-terminal domain of each FliM to form FliM1/FliN3 units whose spiral at the bottom edge of the C ring underlies the cytoplasmic face of the basal body. FliN contributes to the CheY-P binding site of the switch, so that CheY-P binding to FliM and FliN reverses motor rotation, and provides docking sites for FliH of the flagellar type III export apparatus. FliN therefore acts in both flagellar motor switching during chemotaxis and efficient flagellar assembly.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003774 cytoskeletal motor activity | IEA GO_REF:0000120 | MODIFY | Summary: Combined IEA from the FliN family signature and UniRule. The GO term covers generation of torque for rotation of a flagellum, but torque is generated by the stator units acting on FliG, not by FliN. Reason: The essence (FliN is a motor component) is sound, but the activity FliN itself contributes is structural: it forms the FliM1/FliN3 units that make up the lower spiral of the C ring and contributes to the CheY-P binding site. Torque is generated by stator units (MotA/MotB, MotC/MotD) coupling proton flow through the membrane to the FliG torque helix. The row is therefore re-typed to structural molecule activity (GO:0005198), matching the FliM review and the complex-level activity of the switch. This is a lateral correction, not a refinement. The starting motor term includes electrochemical rotation; the replacement is chosen to describe this subunit’s demonstrated structural switch role, not because flagellar motors fall outside GO0003774. Proposed replacements: structural molecule activity Supporting Evidence: PMID:31452860 Each stator unit is composed of two transmembrane proteins, MotA and MotB, and acts as a transmembrane proton channel to couple the proton flow through the channel with torque generation PMID:31452860 A continuous spiral density at the bottom edge of the C ring is made of the C-terminal domains of FliM (FliMC) and FliN. file:PSEPK/fliN/fliN-uniprot.txt DR InterPro; IPR001172; FliN_T3SS_HrcQb. |
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | MODIFY | Summary: FliN is a peripheral membrane protein on the cytoplasmic side of the inner membrane, held there through the C ring and MS ring. Reason: Correct but general. fliN has no transmembrane segment and is held on the cytoplasmic face of the inner membrane through the C ring and MS ring, so the supported membrane location is GO:0009898 cytoplasmic side of plasma membrane, as for FliG and the soluble chemotaxis proteins at receptor arrays. The informative structural location, the C ring, is given on the MODIFY rows below. Proposed replacements: cytoplasmic side of plasma membrane Supporting Evidence: file:PSEPK/fliN/fliN-uniprot.txt SUBCELLULAR LOCATION: Cell membrane {ECO:0000256|RuleBase:RU362074}; Peripheral membrane protein {ECO:0000256|RuleBase:RU362074}; Cytoplasmic side {ECO:0000256|RuleBase:RU362074}. PMID:31452860 The C ring consisting of a cylindrical wall and inner lobes is formed by FliG, FliM and FliN on the cytoplasmic face of the MS ring |
| GO:0006935 chemotaxis | IEA GO_REF:0000002 | ACCEPT | Summary: FliN does part of the work of chemotaxis: it is part of the CheY-P binding site of the switch whose occupancy reverses motor rotation. Reason: CheY-P binds the FliN C-terminal domain in a FliM-dependent manner, and CheY-P binding to FliM and FliN remodels the C ring to switch the motor to CW rotation. FliN is thus a direct participant in the output step of chemotactic signaling. Family-level evidence (E. coli/Salmonella); no KT2440 fliN mutant phenotype is in the cached literature. Supporting Evidence: PMID:31452860 CheY-P binds to FliNC in a FliM-dependent manner [38]. 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 [34]. file:PSEPK/fliN/fliN-uniprot.txt This complex interacts with the CheY and CheZ chemotaxis proteins, in addition to contacting components of the motor that determine the direction of flagellar rotation. |
| GO:0009288 bacterial-type flagellum | IEA GO_REF:0000002 | MODIFY | Summary: Correct but general; FliN is a C ring subunit of the flagellar basal body. Reason: GO:0009433 bacterial-type flagellum basal body, C ring is a part_of descendant of bacterial-type flagellum and is the substructure that contains FliN, so the row is refined to it. Proposed replacements: bacterial-type flagellum basal body, C ring Supporting Evidence: PMID:31452860 The C ring is composed of FliG, FliM and FliN. file:PSEPK/fliN/fliN-uniprot.txt FUNCTION: FliN is one of three proteins (FliG, FliN, FliM) that form the rotor-mounted switch complex (C ring), located at the base of the basal body. |
| GO:0009425 bacterial-type flagellum basal body | IEA GO_REF:0000120 | MODIFY | Summary: Correct but general; within the basal body FliN is a component of the cytoplasmic C ring. Reason: Refined to its part_of descendant GO:0009433 bacterial-type flagellum basal body, C ring, the specific substructure formed by FliG, FliM and FliN. Proposed replacements: bacterial-type flagellum basal body, C ring Supporting Evidence: PMID:31452860 FliM and FliN together form the FliM1/FliN3 complex consisting of one copy of FliM and three copies of FliN [17], and 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:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: Correct but general; the membrane in question is the inner (plasma) membrane, to whose cytoplasmic face the C ring is attached. Reason: Correct but general. FliN has no transmembrane segment and sits on the cytoplasmic face of the inner membrane through the C ring and MS ring, so the generic membrane term is refined to GO:0009898 cytoplasmic side of plasma membrane, the same replacement used for this gene's GO:0005886 row and for FliG. Proposed replacements: cytoplasmic side of plasma membrane Supporting Evidence: file:PSEPK/fliN/fliN-uniprot.txt SUBCELLULAR LOCATION: Cell membrane {ECO:0000256|RuleBase:RU362074}; Peripheral membrane protein {ECO:0000256|RuleBase:RU362074}; Cytoplasmic side {ECO:0000256|RuleBase:RU362074}. |
| GO:0071973 bacterial-type flagellum-dependent cell motility | IEA GO_REF:0000120 | ACCEPT | Summary: FliN is a rotor/switch component of the flagellar motor and also supports flagellar assembly via FliH docking; it does part of the work of flagellum-dependent motility. Reason: As a C ring subunit FliN is part of the rotating motor and its switch. No KT2440 fliN mutant data are cached, so the term is kept at the general motility level rather than refined to swimming. Supporting Evidence: file:PSEPK/fliN/fliN-uniprot.txt FUNCTION: FliN is one of three proteins (FliG, FliN, FliM) that form the rotor-mounted switch complex (C ring), located at the base of the basal body. PMID:31452860 FliN also provides binding sites for FliH, a cytoplasmic component of the flagellar type III protein export apparatus for efficient flagellar protein export and assembly |
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Download this section (compressed HTML)Q: Does KT2440 FliN, like E. coli FliN, dock FliH and contribute to flagellar export, and does a fliN mutant lack flagella or only switching?
Experiment: Construct fliN deletion and C-terminal CheY-P-interface point mutants; score flagellation by staining, swimming and tethered-cell reversal frequency, and FliH co-purification.
Hypothesis: FliN is required both for flagellar assembly and for CheY-P-dependent switching in KT2440.
Type: genetics and motility phenotyping
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