PscC (SctC, PA1716) is the outer-membrane secretin of the type III secretion system of Pseudomonas aeruginosa. It is encoded in the exsD-pscB-L operon of the T3SS locus, whose products are homologues of the Yersinia Ysc export apparatus, and it is made as a precursor with a signal peptide. Many copies assemble into a barrel-shaped, ring-like channel in the outer membrane whose central chamber is plugged in the resting state, the same "cup and saucer" architecture as the type II secretion secretin PulD. The channel anchors the base of the injectisome in the cell envelope and is the conduit through which effector proteins such as exoenzyme S are delivered out of the bacterium and into host cells; loss of the gene abolishes type III secretion, reduces killing of host cells and attenuates virulence in animal infection.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0009279 cell outer membrane | IEA GO_REF:0000120 | ACCEPT | Summary: UniRule/HAMAP (MF_02219) subcellular-location assignment for a T3SS secretin. Reason: HAMAP is a curated rule system, and the location is independently supported - PscC was assayed as an outer-membrane ring-forming secretin in PAO1 depletion strains, and the purified multimer is a membrane-inserted barrel. The gene has no experimental GO row for this location, which is a curation gap rather than a doubt about the claim. Supporting Evidence: PMID:22147293 PilQ, XcpQ, and PscC form multimeric ring-like structures in the OM file:PSEAE/pscC/pscC-uniprot.txt Cell outer membrane |
| GO:0009306 protein secretion | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the YscC outer-membrane pore entry and the shared T2SS/T3SS secretin domain to protein secretion. Reason: Correct but general. IPR004846 is shared with the T2SS secretins, so the combined mapping stops at the generic term; for PscC the specific supported term is GO:0030254 protein secretion by the type III secretion system, which the gene already carries. Proposed replacements: protein secretion by the type III secretion system Supporting Evidence: file:PSEAE/pscC/pscC-uniprot.txt NCBIfam; TIGR02516; type_III_yscC PMID:25156426 The membrane-inserted, multimeric regions of PscC, the |
| GO:0030254 protein secretion by the type III secretion system | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN009110345, the T3SS-secretin subnode of PTHR30332, whose IBD for this term rests solely on the PseudoCAP IMP row for this gene. Reason: The node is the T3SS-specific subnode - the T2SS terms of the same family sit on PTN000768388, and an IRD at the child node PTN009110348 withdraws the T3SS terms in a divergent subclade - so the term suits the clade that inherits it. A single seed is not weak support, and PscC appearing in its own WITH/FROM reflects its experimental seed, as expected. Supporting Evidence: PMID:14977975 exsA gene, which encodes a type III regulatory protein, or pscC, which encodes file:PSEAE/pscC/pscC-uniprot.txt Belongs to the bacterial secretin family. T3SS SctC |
| GO:0030254 protein secretion by the type III secretion system | IMP PMID:8971719 Exoenzyme S of Pseudomonas aeruginosa is secreted by a type ... | ACCEPT | Summary: PseudoCAP IMP from Yahr, Goranson and Frank 1996, the transposon screen that defined the exsD-pscB-L T3SS operon; sole seed of the PTN009110345 IBD (25 leaf IBAs, 15 taxa). Reason: The claim is well founded. The seed paper isolated exoenzyme-S-deficient transposon mutants mapping to this operon and showed the operon encodes homologues of the Yersinia Ysc export apparatus, and later work uses pscC mutants as the canonical secretion-apparatus-null strain - repressed for the T3SS regulon, attenuated in mouse pneumonia, and impaired for T3SS-dependent host cell killing. The cached record is abstract-only and does not say which ORF the mapped insertions lie in, so the gene-level attribution rests on the curator's reading of the full text, which is not grounds to overrule an experimental annotation whose conclusion is independently confirmed. Supporting Evidence: PMID:8971719 isolated which exhibited an exoenzyme S-deficient phenotype (388::Tn5Tc 469, PMID:12421316 mutant in pscC, encoding a structural component of the type III translocase, is PMID:14977975 exsA gene, which encodes a type III regulatory protein, or pscC, which encodes |
| GO:0030254 protein secretion by the type III secretion system | IEA GO_REF:0000104 | ACCEPT | Summary: UniRule/HAMAP (MF_02219) process assignment for a T3SS secretin. Reason: Reinforces the IMP and IBA rows for the same term from a curated rule system; correct and at the right granularity. Supporting Evidence: file:PSEAE/pscC/pscC-uniprot.txt Component of the type III secretion system (T3SS), also called injectisome, which is used to inject bacterial effector proteins |
| GO:0030257 type III protein secretion system complex | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN009110345, whose IBD for this term was seeded by another characterised T3SS secretin rather than by this gene. Reason: Membership in the injectisome is what an SctC secretin is for, and PscC specifically has been purified as the membrane-inserted multimeric channel of the P. aeruginosa T3SS. The node placement is the T3SS subnode, so the inheritance is sound, and the seed being a different family member is ordinary IBD practice rather than a weakness. Supporting Evidence: PMID:25156426 The membrane-inserted, multimeric regions of PscC, the file:PSEAE/pscC/pscC-uniprot.txt This subunit is part of the base, which anchors the injectisome in the bacterial cell envelope |
| GO:0030257 type III protein secretion system complex | IEA GO_REF:0000104 | ACCEPT | Summary: UniRule/HAMAP (MF_02219) complex assignment for a T3SS secretin. Reason: Reinforces the IBA row for the same term from a curated rule system, consistent with the purified PscC multimer and with the rule's statement that the subunit belongs to the injectisome base. Supporting Evidence: file:PSEAE/pscC/pscC-uniprot.txt Forms a stable homooligomeric complex. PMID:25156426 of two distinct rings, with that of PulD being less segmented than that of PscC. |
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Download this section (compressed HTML)Q: Does the plug and hairpin region seen in the cell-free-synthesised PscC multimer correspond to the gate of the assembled injectisome, and what opens it when the needle engages?
Q: Why does PscC, unlike XcpQ, depend on LolB for outer-membrane accumulation - is a lipoprotein pilotin required for its assembly in P. aeruginosa, and which protein is it?
Experiment: Reconstitute PscC in the assembled injectisome base with the inner-membrane ring proteins and resolve the channel with and without a docked needle, to test whether the central plug moves during secretion.
Experiment: Screen candidate lipoproteins for a PscC pilotin by depletion and co-immunoprecipitation in PAO1, using outer-membrane multimer formation as the readout.
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