ZnuC is the ATP-binding, energy-coupling subunit of the high-affinity ZnuABC zinc importer of Pseudomonas aeruginosa PAO1. The transporter is an ABC importer of the metal type: a periplasmic solute-binding protein (ZnuA) delivers Zn(2+) to an inner-membrane permease (ZnuB), and two copies of ZnuC hydrolyse ATP on the cytoplasmic face to drive translocation into the cytosol. ZnuC itself is a 269-residue peripheral inner-membrane protein with a single ABC ATPase domain and a Walker A motif, and it carries no transmembrane segment. The genes are organised in a zur-znuC-znuB operon, which is repressed by the zinc-responsive Fur-family regulator Zur (Np20) when zinc is plentiful and derepressed under zinc limitation; znuA is transcribed separately and is also Zur-repressed. Loss of znuC, znuB or znuA slows growth under metal chelation, although P. aeruginosa has additional, partly redundant routes for zinc acquisition, and the system contributes to the activity of secreted zinc-dependent proteases and to dissemination during infection.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005524 ATP binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro ABC-transporter ATP-binding domain signatures. Swiss-Prot also curates a Walker A ATP-binding site at residues 38-45. Reason: ZnuC is the nucleotide-binding subunit of the importer; ATP binding is its own activity and part of the energy-coupling mechanism. Supporting Evidence: file:PSEAE/znuC/znuC-uniprot.txt FT BINDING 38..45 file:PSEAE/znuC/znuC-uniprot.txt DR Pfam; PF00005; ABC_tran; 1. |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Subcellular-location mapping. ZnuC has no transmembrane segment; it is a peripheral protein on the cytoplasmic face of the inner membrane, where it docks onto the ZnuB permease. Reason: Correct location for the ATPase subunit of an inner-membrane ABC importer, and as precise as the evidence allows. Supporting Evidence: file:PSEAE/znuC/znuC-uniprot.txt Cell inner membrane {ECO:0000255|HAMAP- |
| GO:0010043 response to zinc ion | IBA GO_REF:0000033 | MODIFY | Summary: IBA from PTN001952271, a Gammaproteobacteria node of PTHR42734 whose seven leaves are the ZnuC proteins of H. influenzae, V. cholerae, Salmonella, Y. pestis, E. coli and P. aeruginosa plus one Nematostella ABC-domain fragment. The clade is tight, but the IBD is sole-seeded by this gene's PseudoCAP IMP row, and that row's evidence is a zinc-limitation growth defect, not a response. Reason: The claim is in the right area but names the wrong kind of process. ZnuC is the ATPase of a zinc importer: it performs the import, while the zinc-sensing response in this system is carried out by Zur, which represses the zur-znuC-znuB operon. The supported process is zinc import across the plasma membrane, a descendant of GO:0071577, which the gene already carries by IEA. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: ROLE CONFLATION Sources checked: PANTHER:PTN001952271 · PTN001952271 SOURCE BAD The clade is right (all six bacterial leaves are ZnuC), but the IBD term should be the zinc-import process rather than response to zinc ion. GOA holds 1455 rows with this node in with/from (7 GO_Central, 1448 TreeGrafter). UniProtKB:Q9HT73 · znuC (PA5500) SOURCE BAD Sole seed; the gene appearing in its own with/from is expected because the IMP row is the descendant evidence the curator used. The issue is the term that row carries, not the self-reference. Proposed replacements: zinc ion import across plasma membrane Supporting Evidence: file:PSEAE/znuC/znuC-uniprot.txt Part of the ABC transporter complex ZnuABC involved in zinc file:PSEAE/znuC/znuC-bioinformatics/RESULTS.md GOA holds 1455 GO:0010043 annotations with PTN001952271 in with/from |
| GO:0010043 response to zinc ion | IMP PMID:24086521 The transcriptional regulator Np20 is the zinc uptake regula... | MODIFY | Summary: PseudoCAP IMP, the sole seed of the PTN001952271 IBD. Ellison et al. deleted the putative znuA, znuB and znuC genes and found reduced growth in LB supplemented with 0.5 mM EDTA, with no general growth defect in plain LB. The paper's own focus is the regulator Np20/Zur. Reason: The mutant phenotype supports a role in zinc acquisition, which is zinc import across the inner membrane; "response to zinc ion" attributes the sensing step to the transporter subunit. Note also that the chelator used is EDTA, which is not zinc-specific, so the phenotype alone does not pin the metal; the metal identity comes from the Zur-regulated operon, the E. coli orthology and the curated EC number. Proposed replacements: zinc ion import across plasma membrane Supporting Evidence: PMID:24086521 the inability to express the putative znuA, znuB, or znuC genes resulted in decreased growth at 18 hours as compared wild-type strain PAO1 when the strains were grown in LB media supplemented with 0.5 mM EDTA PMID:24086521 First identified in Escherichia coli, this ABC-type transport system is comprised of a zinc-binding periplasmic protein (ZnuA), an inner membrane permease (ZnuB), and an ATPase (ZnuC) |
| GO:0015633 ABC-type zinc transporter activity | IEA GO_REF:0000120 | ACCEPT | Summary: Mapping from the curated EC number and Rhea reaction on the UniProt entry (Zn(2+) outside plus ATP inside giving Zn(2+) inside, ADP and phosphate). This is the activity of the ZnuABC complex, to which ZnuC contributes the ATPase. Reason: Core activity and the most specific transporter term supported for this protein. Because the reaction requires ZnuA, ZnuB and ZnuC together, contributes_to would be a better qualifier than enables (flagged to UniProt below). Supporting Evidence: file:PSEAE/znuC/znuC-uniprot.txt Reaction=Zn(2+)(out) + ATP(in) + H2O(in) = Zn(2+)(in) + ADP(in) + file:PSEAE/znuC/znuC-uniprot.txt The complex is composed of two ATP-binding proteins (ZnuC), |
| GO:0016887 ATP hydrolysis activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro ABC ATPase signatures. ATP hydrolysis is the step ZnuC itself performs within the transport cycle. Reason: The subunit's own catalytic activity, and the basis of its energy-coupling role in the importer. Supporting Evidence: file:PSEAE/znuC/znuC-uniprot.txt Responsible for energy coupling to the transport system. |
| GO:0042626 ATPase-coupled transmembrane transporter activity | IBA GO_REF:0000033 | MODIFY | Summary: IBA from the PTHR42734 family root PTN002448841 (90 leaves), whose donor is E. coli BtuD (P06611), the vitamin B12 importer ATPase. A generic ABC-importer term, correct but not specific to this protein's substrate. Reason: True but less specific than the evidence supports: the substrate of this subfamily is zinc, and GO:0015633 ABC-type zinc transporter activity (a descendant, already on the gene from the curated EC number) is the supported term. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002448841 · PTN002448841 (PTHR42734 root) SUPPORTS TRANSFER A family-root assertion over metal and vitamin-B12 ABC importer ATPases; the generic term is appropriate for the root, and the specific substrate comes from the subfamily. UniProtKB:P06611 · E. coli BtuD SUPPORTS TRANSFER Characterized ABC importer ATPase; supports the generic activity, not the zinc specificity. Proposed replacements: ABC-type zinc transporter activity Supporting Evidence: file:PSEAE/znuC/znuC-uniprot.txt DR PROSITE; PS51298; ZNUC; 1. |
| GO:0043190 ATP-binding cassette (ABC) transporter complex | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from the family root. ZnuC is a subunit of the ZnuABC complex, as curated in the UniProt SUBUNIT line. Reason: Correct complex membership for the ATPase subunit, supported independently of the phylogenetic transfer by the curated subunit composition. Supporting Evidence: file:PSEAE/znuC/znuC-uniprot.txt The complex is composed of two ATP-binding proteins (ZnuC), two transmembrane proteins (ZnuB) and a solute-binding protein (ZnuA). PMID:24086521 First identified in Escherichia coli, this ABC-type transport system is comprised of a zinc-binding periplasmic protein (ZnuA), an inner membrane permease (ZnuB), and an ATPase (ZnuC) |
| GO:0055085 transmembrane transport | IEA GO_REF:0000108 | MODIFY | Summary: Automatic process term derived from the generic transporter activity above. Reason: True but uninformative; the supported process is zinc import across the plasma membrane, a descendant of this term. Proposed replacements: zinc ion import across plasma membrane Supporting Evidence: file:PSEAE/znuC/znuC-uniprot.txt Part of the ABC transporter complex ZnuABC involved in zinc |
| GO:0071577 zinc ion transmembrane transport | IEA GO_REF:0000108 | MODIFY | Summary: Automatic process term derived from the ABC-type zinc transporter activity. Correct, and the right substrate. Reason: Correct but less specific than the evidence supports: ZnuABC is an importer at the inner membrane, so the directional descendant GO:0071578 zinc ion import across plasma membrane is the supported term. Proposed replacements: zinc ion import across plasma membrane Supporting Evidence: file:PSEAE/znuC/znuC-uniprot.txt Reaction=Zn(2+)(out) + ATP(in) + H2O(in) = Zn(2+)(in) + ADP(in) + |
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Download this section (compressed HTML)Q: Should PTN001952271's IBD be re-pointed from GO:0010043 response to zinc ion to a zinc-import process term, given that all its bacterial leaves are ZnuC subunits and 1448 of its 1455 propagated rows are TreeGrafter transfers?
Q: Which transporter accounts for the zinc that P. aeruginosa still acquires when ZnuABC is inactivated, given that intracellular zinc is barely affected in a znuA mutant?
Experiment: Measure radiolabelled zinc uptake in inner-membrane vesicles or in proteoliposomes reconstituted with ZnuA, ZnuB and ZnuC, with and without ATP and with a Walker A lysine variant of ZnuC. This would establish the transport reaction and its ATPase requirement directly, rather than through a chelated-medium growth phenotype, and would let the EC number be supported experimentally for the P. aeruginosa system.
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