PA1055 encodes the subunit C (ShaC/MrpC) of the Sha (Mrp/Mnh/Pha) multisubunit Na+/H+ antiporter of Pseudomonas aeruginosa PAO1. It is a small integral membrane protein of 112 residues with two predicted transmembrane helices, homologous to the NuoK (ND4L) subunit of respiratory complex I. PA1055 is the second gene of the six-gene sha cluster PA1054-PA1059, in which shaA and shaB are fused. The cluster expressed in an E. coli strain lacking its major Na+/H+ antiporters restores Na+ tolerance and Na+/H+ antiport. In P. aeruginosa the Sha antiporter is largely responsible for Na+ extrusion, and loss of ShaA causes Na+ sensitivity and attenuated virulence in mouse infection models. In Mrp antiporters, activity needs the hetero-oligomeric complex of all subunits. Structures of Bacillus Mrp place subunit C next to the C-terminal domain of MrpA and MrpD, in a hydrated region proposed to form part of the Na+ pathway.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Subcellular location mapping (cell membrane, multi-pass). PA1055 has two predicted TM helices and is a subunit of an inner-membrane Na+/H+ antiporter complex. Reason: Correct location; the Mrp/Sha complex extrudes Na+ across the cytoplasmic membrane. Supporting Evidence: file:PSEAE/PA1055/PA1055-uniprot.txt TRANSMEM 32..57 PMID:16030218 genes PA1054 to PA1059 encode a Na+/H+ antiporter that is largely responsible for Na+ extrusion in P. aeruginosa |
| GO:0015385 sodium:proton antiporter activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN002160376, the LUCA root of PTHR34583 (Mrp/Mnh subunit C family, 24 reference leaves), sole-seeded by the PseudoCAP IMP row for this gene. PA1055 is ShaC of the Sha Na+/H+ antiporter. The antiport activity belongs to the hetero-oligomeric complex, so a subunit contributes to it rather than enabling it alone. The node also covers MBH/MBX hydrogenase subunits (TK2086, TK1221) whose complexes are not stand-alone antiporters. Reason: The core activity of the complex this protein belongs to; kept. The qualifier should be contributes_to (GO_CENTRAL defect below). The seed shows the activity for the whole cluster, not for PA1055 alone. Propagation Review Root cause: SOURCE WEAK OR INFERRED Sources checked: PANTHER:PTN002160376 · PTN002160376 SUPPORTS TRANSFER Family-root IBD; right for Mrp/Mnh/Pha subunit C proteins as a contribution to complex activity. It reaches MBH/MBX hydrogenase subunits, where a Na+/H+ antiporter MF is doubtful. UniProtKB:Q9I4R9 · PA1055 (shaC) SOURCE WEAK OR INFERRED Sole seed; PseudoCAP IMP, but the PMID:16030218 abstract reports a disruption of PA1054 only. The cluster-level complementation supports a contribution by the complex; an IMP for this gene is not shown in the abstract. Supporting Evidence: PMID:16030218 The gene cluster PA1054 to PA1059, but not the cluster with a deletion of PA1054, complemented a growth defect in the presence of 0.2 M NaCl and a defect in Na+/H+ antiport activity of the Escherichia coli TO114 mutant lacking the three major Na+/H+ antiporters PMID:20624916 Antiport activity requires hetero-oligomeric complexes of all six or seven hydrophobic Mrp proteins (MrpA-MrpG). file:PSEAE/PA1055/PA1055-bioinformatics/RESULTS.md PTN002160376 is the root of the PTHR34583 tree (LUCA speciation node, is_family_root: True): 24 leaves in 19 organisms. |
| GO:0015385 sodium:proton antiporter activity | IMP PMID:16030218 Characterization of a multigene-encoded sodium/hydrogen anti... | ACCEPT | Summary: PseudoCAP IMP, the sole seed of the PTN002160376 antiporter IBD. Kosono et al. showed that the six-gene cluster PA1054-PA1059 restores Na+/H+ antiport to an antiporter-deficient E. coli strain, and that it fails to do so when PA1054 is deleted. The abstract reports a P. aeruginosa disruption of PA1054 only and describes no PA1055 mutant, and the full text (read 2026-11-05) confirms none was made, so a mutant-phenotype code is wrong for PA1055. The evidence supports PA1055 as a subunit of the Sha antiporter complex. Reason: The claim that PA1055 is part of the Na+/H+ antiporter is right, so kept as the core activity. But it is a contribution to complex activity (contributes_to), and the evidence in the abstract is cluster complementation, not a PA1055 mutant phenotype. Both are flagged to PseudoCAP. Supporting Evidence: PMID:16030218 The gene cluster PA1054 to PA1059, but not the cluster with a deletion of PA1054, complemented a growth defect in the presence of 0.2 M NaCl and a defect in Na+/H+ antiport activity of the Escherichia coli TO114 mutant lacking the three major Na+/H+ antiporters PMID:29218041 Generally, all Mrp subunits, mrpA-G, are required for enzymatic activity. |
| GO:0035725 sodium ion transmembrane transport | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN002160376 (subunit C family root), sole-seeded by the PseudoCAP IMP row. Subunit C of Mrp-type complexes, including the Mrp-like module of archaeal MBH, takes part in Na+ translocation. The term suits the clade. Reason: Core process of the Sha complex, in which this subunit participates; Mrp structures place subunit C at the putative Na+ pathway. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002160376 · PTN002160376 SUPPORTS TRANSFER Na+ transmembrane transport fits Mrp antiporter subunits and the Na+-translocating modules of MBH-type complexes. UniProtKB:Q9I4R9 · PA1055 (shaC) SOURCE WEAK OR INFERRED Sole seed; process supported by cluster-level evidence, but the IMP code looks wrong for PA1055 (see the IMP row). Supporting Evidence: PMID:16030218 genes PA1054 to PA1059 encode a Na+/H+ antiporter that is largely responsible for Na+ extrusion in P. aeruginosa PMID:36241630 the pronounced hydration in the vicinity of MrpC suggests a role in sodium transfer PMID:29754813 The Na+-translocating unit, absent in complex I, resembles that found in the Mrp H+/Na+ antiporter |
| GO:0035725 sodium ion transmembrane transport | IMP PMID:16030218 Characterization of a multigene-encoded sodium/hydrogen anti... | ACCEPT | Summary: PseudoCAP IMP, the sole seed of the PTN002160376 Na+ transport IBD. The Sha cluster is responsible for Na+ efflux, and PA1054 disruption lowers Na+ efflux. PA1055, as a subunit of the complex, takes part in this transport. The IMP code looks wrong for PA1055 (no PA1055 mutant in the abstract). Reason: Process correct for this subunit of the Na+-extruding complex; evidence code flagged. Supporting Evidence: PMID:16030218 genes PA1054 to PA1059 encode a Na+/H+ antiporter that is largely responsible for Na+ extrusion in P. aeruginosa |
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Download this section (compressed HTML)Q: Should GO provide a cellular component term for the Mrp-type multisubunit Na+/H+ antiporter complex, by analogy with GO:1903103 potassium:proton antiporter complex, so that Sha/Mrp subunits can be annotated to the complex instead of each carrying the activity?
Q: Should the subunit C IBD at PTN002160376 reach MBH/MBX hydrogenase subunits (TK2086, TK1221)? Is a Na+/H+ antiporter MF appropriate for those complexes?
Experiment: Make an in-frame PA1055 (shaC) deletion in P. aeruginosa, then measure Na+ tolerance, Na+ efflux and Sha complex assembly (BN-PAGE), with complementation in trans. In parallel, express the cluster lacking only PA1055 in E. coli TO114 and assay Na+/H+ antiport in everted vesicles.
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