mexA (PA0425) encodes MexA, the periplasmic adaptor (membrane fusion protein) of the MexAB-OprM resistance-nodulation-cell division (RND) multidrug efflux pump, the main constitutive efflux system of Pseudomonas aeruginosa. MexA is a lipoprotein anchored to the inner membrane; six MexA molecules form a funnel that joins the MexB transporter trimer to the outer-membrane channel OprM, and MexA is needed for MexB proton-coupled transport and for opening of OprM. The pump expels beta-lactams, fluoroquinolones, tetracycline, chloramphenicol, macrolides and other compounds, including the quorum-sensing signal 3-oxo-C12-homoserine lactone, and is a major determinant of intrinsic multidrug resistance.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN001249140 (seeds E. coli AcrA, MdtE). MexA is anchored to the inner membrane. Reason: Shown structurally for the assembled pump. Supporting Evidence: PMID:30944318 MexA, which is anchored to the inner membrane PMID:33009415 MexB-trio is surrounded by six molecules of MexA anchored in the lipid membrane. |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (cell inner membrane). Reason: Agrees with the structural data. Supporting Evidence: PMID:30944318 MexA, which is anchored to the inner membrane |
| GO:0015297 antiporter activity | IDA PMID:33009415 Antibiotic export by MexB multidrug efflux transporter is al... | ACCEPT | Summary: contributes_to antiporter activity: in proteoliposomes MexB proton-coupled transport needs MexA (and OprM). Reason: MexB is the proton/drug antiporter; MexA is required for its activity, so contributes_to is right. Supporting Evidence: PMID:33009415 in the absence of MexA almost no proton transport is measured for MexB-solo despite the presence of substrate |
| GO:0015562 efflux transmembrane transporter activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN001249140 with MexA itself as the source; MexA in its own WITH/FROM reflects its own experimental evidence. Reason: The activity belongs to the assembled tripartite pump, to which MexA contributes as the adaptor that is required for MexB transport; contributes_to is the more precise qualifier for an adaptor, but the claim is accepted. Supporting Evidence: PMID:25901994 By combining proteoliposomes containing the MexAB and OprM portions of the complex, we are able to assay energy-dependent substrate translocation in a system that mimics the dual-membrane architecture of Gram-negative bacteria. PMID:33009415 in the absence of MexA almost no proton transport is measured for MexB-solo despite the presence of substrate |
| GO:0015562 efflux transmembrane transporter activity | IDA PMID:25901994 In vitro transport activity of the fully assembled MexAB-Opr... | ACCEPT | Summary: In vitro transport by reconstituted MexAB-OprM (abstract only). Reason: The activity belongs to the assembled tripartite pump, to which MexA contributes as the adaptor that is required for MexB transport; contributes_to is the more precise qualifier for an adaptor, but the claim is accepted. Supporting Evidence: PMID:25901994 By combining proteoliposomes containing the MexAB and OprM portions of the complex, we are able to assay energy-dependent substrate translocation in a system that mimics the dual-membrane architecture of Gram-negative bacteria. |
| GO:0015562 efflux transmembrane transporter activity | IDA PMID:33009415 Antibiotic export by MexB multidrug efflux transporter is al... | ACCEPT | Summary: contributes_to efflux transporter activity, from reconstitution of MexB with MexA and OprM. Reason: Correct qualifier and term for the adaptor subunit. Supporting Evidence: PMID:33009415 in the absence of MexA almost no proton transport is measured for MexB-solo despite the presence of substrate PMID:33009415 Functional assay using MexAB-OprM system reconstituted in liposomes has shown an efficient drug transport correlated with a proton gradient |
| GO:0015562 efflux transmembrane transporter activity | IMP PMID:9973347 Active efflux and diffusion are involved in transport of Pse... | ACCEPT | Summary: Efflux of 3OC12-HSL needs the mexA-mexB-oprM pump (abstract only; mutant lacking the whole operon). Reason: The activity belongs to the assembled tripartite pump, to which MexA contributes as the adaptor that is required for MexB transport; contributes_to is the more precise qualifier for an adaptor, but the claim is accepted. Supporting Evidence: PMID:9973347 Instead, the mexA-mexB-oprM-encoded efflux pump is involved in active efflux of 3OC12-HSL. |
| GO:0016020 membrane | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO from the MFP family signature. Reason: Plasma membrane (GO:0005886), accepted in this review, is_a membrane. Supporting Evidence: PMID:30944318 MexA, which is anchored to the inner membrane |
| GO:0022857 transmembrane transporter activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO from the MFP family signatures. Reason: GO:0015562 efflux transmembrane transporter activity, accepted in this review, is_a transmembrane transporter activity. Supporting Evidence: PMID:25901994 By combining proteoliposomes containing the MexAB and OprM portions of the complex, we are able to assay energy-dependent substrate translocation in a system that mimics the dual-membrane architecture of Gram-negative bacteria. |
| GO:0030313 cell envelope | IDA PMID:11114896 Mutational analysis of the OprM outer membrane component of ... | ACCEPT | Summary: is_active_in cell envelope, from the OprM mutational study. Reason: The active MexAB-OprM pump spans inner membrane, periplasm and outer membrane, so the cell envelope is the right scope for where it acts; plasma membrane is not part_of cell envelope in GO, so neither entails the other. Supporting Evidence: PMID:11114896 a periplasmic but cytoplasmic membrane-anchored membrane fusion protein ( 15 ) (MexA, MexC, MexE, and MexX) PMID:30944318 MexB does not directly contact OprM; instead, MexA joins MexB and OprM by forming a funnel-like hexamer. |
| GO:0042802 identical protein binding | IMP PMID:15226509 Structure of the periplasmic component of a bacterial drug e... | KEEP AS NON CORE | Summary: Identical protein binding from the MexA crystal structure paper (abstract only): MexA hairpins pack side by side in the crystal. Reason: MexA self-association is real: it forms a hexamer in the assembled pump. It is a structural property of the adaptor rather than its function. Supporting Evidence: PMID:15226509 In the crystal, hairpins of neighboring MexA monomers pack side-by-side to form twisted arcs. PMID:30944318 MexB does not directly contact OprM; instead, MexA joins MexB and OprM by forming a funnel-like hexamer. |
| GO:0046618 xenobiotic export from cell | IDA PMID:33009415 Antibiotic export by MexB multidrug efflux transporter is al... | ACCEPT | Summary: Xenobiotic export from cell, from the reconstitution study. Reason: Correct; the pump exports drugs out of the cell. GO:0140330 is the more specific route-based term, but it is not a descendant of this one in GO. Supporting Evidence: PMID:33009415 Functional assay using MexAB-OprM system reconstituted in liposomes has shown an efficient drug transport correlated with a proton gradient |
| GO:0046677 response to antibiotic | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA from PTN001249140, seeded by E. coli AcrA and MdtE, MexX and MexA itself. Reason: True resistance-phenotype term for an efflux component, but the core role is export, captured by GO:0140330. Non-core, as for mexX and PA3677 (mexJ). The IBD stands on the E. coli seeds alone. Supporting Evidence: PMID:8540696 Thus, the steady-state accumulation levels of tetracycline and norfloxacin were increased in mexA and oprM null mutants. |
| GO:0046677 response to antibiotic | IDA PMID:8540696 Role of mexA-mexB-oprM in antibiotic efflux in Pseudomonas a... | KEEP AS NON CORE | Summary: PseudoCAP IDA from Li, Nikaido and Poole 1995 (abstract only), a seed of the PTN001249140 IBD. mexA null mutants accumulate more drug and are more susceptible. Seed verdict SOUND; the evidence code should be IMP. Reason: True resistance-phenotype term for an efflux component, but the core role is export, captured by GO:0140330. Non-core, as for mexX and PA3677 (mexJ). The data are mutant phenotypes, recorded as an evidence-code defect. Supporting Evidence: PMID:8540696 Thus, the steady-state accumulation levels of tetracycline and norfloxacin were increased in mexA and oprM null mutants. PMID:8540696 These results support the notion that these proteins contribute to the intrinsic resistance of P. aeruginosa through the multidrug active efflux process. |
| GO:0051260 protein homooligomerization | IMP PMID:15226509 Structure of the periplasmic component of a bacterial drug e... | KEEP AS NON CORE | Summary: Protein homooligomerization from the MexA crystal structure paper (abstract only). Reason: MexA forms a hexamer in the pump; true but a structural property rather than the function. Supporting Evidence: PMID:30944318 MexB does not directly contact OprM; instead, MexA joins MexB and OprM by forming a funnel-like hexamer. |
| GO:0055085 transmembrane transport | IDA PMID:33009415 Antibiotic export by MexB multidrug efflux transporter is al... | TOO GENERAL | Summary: Transmembrane transport by reconstituted pump. Reason: GO:0140330, accepted in this review, is_a transmembrane transport. Supporting Evidence: PMID:33009415 Functional assay using MexAB-OprM system reconstituted in liposomes has shown an efficient drug transport correlated with a proton gradient |
| GO:0055085 transmembrane transport | IEA GO_REF:0000120 | TOO GENERAL | Summary: Combined IEA from MFP signatures. Reason: GO:0140330, accepted in this review, is_a transmembrane transport. Supporting Evidence: PMID:33009415 Functional assay using MexAB-OprM system reconstituted in liposomes has shown an efficient drug transport correlated with a proton gradient |
| GO:0055085 transmembrane transport | IMP PMID:9973347 Active efflux and diffusion are involved in transport of Pse... | TOO GENERAL | Summary: 3OC12-HSL efflux requires the pump (abstract only). Reason: GO:0140330, accepted in this review, is_a transmembrane transport. Supporting Evidence: PMID:9973347 Instead, the mexA-mexB-oprM-encoded efflux pump is involved in active efflux of 3OC12-HSL. |
| GO:0140330 xenobiotic detoxification by transmembrane export across the cell outer membrane | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN001249140, seeded by E. coli AcrA, AcrE and MexA itself. Reason: Core process of the tripartite pump; MexA has its own IDA for the term. Supporting Evidence: PMID:25901994 By combining proteoliposomes containing the MexAB and OprM portions of the complex, we are able to assay energy-dependent substrate translocation in a system that mimics the dual-membrane architecture of Gram-negative bacteria. PMID:30944318 MexB does not directly contact OprM; instead, MexA joins MexB and OprM by forming a funnel-like hexamer. |
| GO:0140330 xenobiotic detoxification by transmembrane export across the cell outer membrane | IDA PMID:25901994 In vitro transport activity of the fully assembled MexAB-Opr... | ACCEPT | Summary: Energy-dependent substrate translocation by reconstituted MexAB-OprM in a two-membrane proteoliposome system (abstract only). Reason: Direct assay of export across both membranes by the assembled pump. Supporting Evidence: PMID:25901994 By combining proteoliposomes containing the MexAB and OprM portions of the complex, we are able to assay energy-dependent substrate translocation in a system that mimics the dual-membrane architecture of Gram-negative bacteria. |
| GO:1990281 efflux pump complex | IDA PMID:25901994 In vitro transport activity of the fully assembled MexAB-Opr... | ACCEPT | Summary: Efflux pump complex, from the reconstitution study. Reason: MexA is the adaptor subunit. Supporting Evidence: PMID:25901994 By combining proteoliposomes containing the MexAB and OprM portions of the complex, we are able to assay energy-dependent substrate translocation in a system that mimics the dual-membrane architecture of Gram-negative bacteria. |
| GO:1990281 efflux pump complex | IDA PMID:30944318 Structures of the wild-type MexAB-OprM tripartite pump revea... | ACCEPT | Summary: Efflux pump complex, cryo-EM of the wild-type MexAB-OprM pump. Reason: Structure of the assembled complex. Supporting Evidence: PMID:30944318 MexB does not directly contact OprM; instead, MexA joins MexB and OprM by forming a funnel-like hexamer. |
| GO:1990281 efflux pump complex | IDA PMID:33009415 Antibiotic export by MexB multidrug efflux transporter is al... | ACCEPT | Summary: Efflux pump complex in nanodiscs. Reason: Structure of the assembled complex. Supporting Evidence: PMID:33009415 MexB-trio is surrounded by six molecules of MexA anchored in the lipid membrane. |
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Download this section (compressed HTML)Q: Does MexA act only as a structural adaptor, or does it allosterically gate MexB, as the chaperone-like MexA-OprM model proposes?
Experiment: Compare transport kinetics of MexB reconstituted with wild-type MexA and with MexA mutants in the MP and beta-barrel domains that still assemble but cannot contact MexB.
Type: in vitro transport assay
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