MotB (PA4953) is the B subunit of the MotAB flagellar stator of Pseudomonas aeruginosa. It has a single N-terminal transmembrane helix in the inner membrane and a periplasmic OmpA-like peptidoglycan-binding domain, and together with MotA (PA4954) forms an ion-conducting stator unit that generates torque at the flagellar rotor. P. aeruginosa has a second stator, MotCD (PA1460-PA1461), and the two are largely redundant: either supports swimming, and loss of both MotB homologues abolishes motility. MotCD is the stator needed for swarming on firmer surfaces, whereas MotAB is dispensable for swarming and, at high c-di-GMP, is needed for repression of swarming, probably by displacing MotCD from the motor.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping; the UniProt location line is ARBA-predicted. Reason: MotB is an inner-membrane stator subunit with one TM helix (Phobius) and belongs to the MotB family; the stator complex is a plasma membrane protein complex. The ARBA line is not evidence by itself, but the TM prediction and the stator role agree with it. Supporting Evidence: file:PSEAE/motB/motB-uniprot.txt TRANSMEM 26..45 PMID:15629949 the stator (the stationary component of the motor within which the rotor turns), which is composed of two integral membrane proteins, MotA and MotB |
| GO:0016020 membrane | IEA GO_REF:0000104 | MODIFY | Summary: UniRule transfer of a generic membrane location. Reason: Correct but general; the specific location is plasma membrane, which the gene already carries (IEA, accepted above). Proposed replacements: plasma membrane Supporting Evidence: file:PSEAE/motB/motB-uniprot.txt TRANSMEM 26..45 |
| GO:0071973 bacterial-type flagellum-dependent cell motility | IMP PMID:15375113 The complex flagellar torque generator of Pseudomonas aerugi... | ACCEPT | Summary: Doyle et al. 2004 (who call PA4953 "motD"): loss of both MotB homologues abolishes motility. Reason: Core process. MotB is a stator subunit and does part of the work of flagellar rotation; the phenotype appears only when the redundant MotCD stator is also removed, which fits a stator shared with a paralogue. Supporting Evidence: PMID:15375113 Mutation of both genes encoding the MotA homologs or MotB homologs was sufficient to abolish motility. PMID:15629949 The double mutant lacking both motAB and motBC can neither swim nor swarm under any conditions tested, but still makes a flagellum. |
| GO:0071978 bacterial-type flagellum-dependent swarming motility | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PAINT IBA from PTN001251133, sole seed the PseudoCAP IMP swarming rows on this protein (expected self-reference for a seed). Reason: For P. aeruginosa MotB the term is a defensible context statement (MotAB alone supports swarming on soft agar), but it is not the core role, and the node term is too specific for the clade. Swarming is a lifestyle phenotype; the nine leaves include Thermodesulfovibrio MotB, Bradyrhizobium PomB, Xanthomonas MotB and the Yersinia/E. coli LafU lateral-flagellum stator (truncated in E. coli K-12), none of which rests on swarming data here. The clade-wide claim is GO:0071973 flagellum-dependent cell motility, with the stator complex already at the node. See the GO_CENTRAL defect. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH CONTEXT OR TISSUE MISMATCH Sources checked: PANTHER:PTN001251133 Β· PTN001251133 SOURCE WEAK OR INFERRED PAINT leaf GAF (cached 2026-10-28) lists 9 GO:0071978 leaves (E. coli MotB and LafU, Salmonella MotB, Yersinia MotB and LafU, Xanthomonas MotB, Bradyrhizobium PomB, Thermodesulfovibrio MotB, PA4953); swarming is a lifestyle context not shown for most. UniProtKB:Q9HUL2 Β· motB SOURCE WEAK OR INFERRED Sole seed (expected self-reference). The IMP rows rest on a double mutant; the single motAB mutant swarms like or better than wild type. Supporting Evidence: PMID:15629949 The fact that the motCD mutant, but not the motAB mutant, has a phenotype with respect to swarming suggests that these two stators may have different roles in swarming motility. |
| GO:0071978 bacterial-type flagellum-dependent swarming motility | IMP PMID:15629949 Evidence for two flagellar stators and their role in the mot... | KEEP AS NON CORE | Summary: PseudoCAP IMP from Toutain et al. 2005 (PA14). The motAB deletion swarms like wild type; the motAB motCD double deletion does not swarm. Reason: The authors conclude both stators act in swarming, and MotAB alone (in the motCD mutant) supports swarming on 0.45% agar, so the stator does take part in the swarming motor. But the single-gene phenotype is wild type, MotCD is the stator swarming depends on, and multicopy MotAB inhibits swarming. Context-specific, non-core; the evidence is a genetic interaction rather than a motB mutant phenotype. Supporting Evidence: PMID:15629949 we conclude that the MotAB and MotBC proteins are stators that play a role in flagellar motor function for both swimming and swarming motility. PMID:15629949 The double mutant Ξ motAB Ξ motCD is not able to swarm under any of the conditions tested. |
| GO:0071978 bacterial-type flagellum-dependent swarming motility | IMP PMID:25349157 Cyclic di-GMP-mediated repression of swarming motility by Ps... | KEEP AS NON CORE | Summary: PseudoCAP IMP from Kuchma et al. 2015 (PA14; abstract only): mutating motAB increases swarming and relieves c-di-GMP repression of swarming. Reason: The stator is physically part of the motor during swarming, so a context-specific involved_in is not false; but the reported phenotype is the opposite of a requirement (the mutant swarms more), and the paper's finding is that MotAB is needed for c-di-GMP-mediated repression of swarming. Full text not available to check what else was assayed, so kept rather than changed; see the PSEUDOCAP defect. Supporting Evidence: PMID:25349157 Here we show that the repression of swarming motility requires a functional MotAB stator complex. |
| GO:0120101 bacterial-type flagellum stator complex | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN001251133, seeded by E. coli MotB (P0AF06). Reason: Core location. PA4953 is the closest P. aeruginosa homologue of E. coli MotB, shares its stator residues, and is described experimentally as one of two stator complexes of the polar flagellum. Propagation Review Root cause: NO FAILURE CORE Sources checked: UniProtKB:P0AF06 Β· E. coli MotB SUPPORTS TRANSFER Seed of the stator complex IBD; PA4953 is the closest P. aeruginosa homologue (38% identity). Supporting Evidence: PMID:25349157 P. aeruginosa encodes two stator complexes, MotAB and MotCD, that participate in the function of its single polar flagellum. PMID:15629949 coli MotB protein has a higher percent identity to PA4953 (38%) than to PA1461 (27%). |
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Download this section (compressed HTML)Q: Does MotAB restrain swarming by occupying motor stator sites (displacing MotCD), or does it actively generate a different torque output on surfaces?
Experiment: Count MotB-containing and MotD-containing stator units per motor by fluorescence of functional chromosomal fusions in cells on swarm agar at low and high c-di-GMP, alongside motor torque measurements, to test the stator-exchange model.
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