XcpV (PA3099, also PddC) is the GspI-family minor pseudopilin of the Xcp type II secretion system of Pseudomonas aeruginosa, the machine that exports elastase, lipases and other exoproteins from the periplasm across the outer membrane. It is made as a prepilin-like precursor whose short leader is removed by the prepilin peptidase PilD/XcpA, which also N-methylates the new N-terminal phenylalanine; the mature protein is anchored in the inner membrane and has a small type IV pilin-like periplasmic domain. XcpV nucleates the pseudopilus tip complex, binding XcpX and XcpW at different sites; with XcpW it forms the core of the tip, and it is required for type II secretion.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | EXP PMID:8331069 Cleavage, methylation, and localization of the Pseudomonas a... | ACCEPT | Summary: UniProt EXP annotation from Nunn and Lory 1993, who localised XcpT-W to the inner membrane by cell fractionation. Reason: Fractionation of wild-type and pilD mutant cells placed XcpV precursor and mature forms in the inner membrane, which is the plasma membrane of a Gram-negative bacterium. Supporting Evidence: PMID:8331069 the precursor forms of XcpT-W are located predominantly in the bacterial inner membrane, and their localization is not altered after PilD-mediated removal of the leader sequence |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (cell inner membrane) to plasma membrane. Reason: Consistent with the experimental inner-membrane localisation (PMID:8331069). Supporting Evidence: PMID:8331069 the precursor forms of XcpT-W are located predominantly in the bacterial inner membrane |
| GO:0015627 type II protein secretion system complex | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN002446181, whose IBD rests solely on the PseudoCAP IDA row for XcpV citing PMID:8331069. Reason: Correct for XcpV, which is part of the XcpU-V-W-X tip complex (PMID:19828448) and the crystallised XcpVW/XcpVWX complexes (PMID:30346996); XcpV in its own WITH/FROM reflects its seed. The node is nevertheless the root of PTHR38779, and the topology (panther_tree.py, 2026-11-05) shows that its two deepest branches are generic prepilins (Aquifex ppdD3 "Pilin", Thermodesulfovibrio THEYE_A0597) while every T2SS-named leaf falls inside the Proteobacteria child PTN002215342. The PilV- and MshD-named proteins that also carry this IBA (14 of its 49 current QuickGO leaves, including Neisseria gonorrhoeae PilV NGO_0453) are not in the reference tree at all: they are non-reference members grafted into the family by sequence. The T2SS complex term is therefore held one node too high and leaks to PilV-type minor pilins; flagged to GO Central. Supporting Evidence: PMID:19828448 We found an XcpV(I)-W(J)-X(K) complex, which demonstrates that the crystallized trimeric complex also exists in the P. aeruginosa T2SS file:PSEAE/xcpV/xcpV-bioinformatics/RESULTS.md The real fault is narrower: the IBD sits one node above PTN002215342 (Proteobacteria, 10 leaves), which holds every T2SS-named leaf including XcpV, while the root also covers two deep generic prepilins. |
| GO:0015627 type II protein secretion system complex | IDA PMID:8331069 Cleavage, methylation, and localization of the Pseudomonas a... | ACCEPT | Summary: PseudoCAP IDA from Nunn and Lory 1993 (PilD cleavage, N-methylation and inner-membrane localisation of XcpT-W); sole seed of the GO:0015627 IBD at PTN002446181. Reason: The term is correct; XcpV nucleates the pseudopilus tip complex (PMID:19828448) and forms the XcpVW core (PMID:30346996). The cited paper, as far as its abstract shows, assays processing, methylation and membrane fractionation, not complex membership. Full text is not in PMC, so the row is kept, with a suspected-level note that a complex-membership paper (PMID:19828448) would be the better reference. Supporting Evidence: PMID:8331069 Four components of the apparatus of extracellular protein secretion of Pseudomonas aeruginosa, Xcpt, -U, -V, and -W (XcpT-W), are synthesized as precursors with short N-terminal leader peptides PMID:19828448 We propose a model in which XcpV(I) is the nucleator that first binds XcpX(K) and XcpW(J) at different sites |
| GO:0015627 type II protein secretion system complex | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the GspI C-terminal domain (IPR003413) and GspI family (IPR010052) entries. Reason: GspI (NCBIfam TIGR01707) is a T2SS-specific minor pseudopilin family; the mapping is correct and confirmed experimentally for XcpV. Supporting Evidence: file:PSEAE/xcpV/xcpV-uniprot.txt NCBIfam; TIGR01707; gspI; 1. PMID:19828448 We found an XcpV(I)-W(J)-X(K) complex, which demonstrates that the crystallized trimeric complex also exists in the P. aeruginosa T2SS |
| GO:0015628 protein secretion by the type II secretion system | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN002446181, whose IBD rests solely on the PseudoCAP IDA row for XcpV citing the review PMID:9818381. Reason: Correct for XcpV (mutant has the lowest LasB secretion of the minor pseudopilin mutants and is complemented; PMID:30346996). The seed's evidence code is wrong (IDA on a review) but primary mutant evidence exists. As for the GO:0015627 IBD at the same node, the tree (panther_tree.py, 2026-11-05) shows the IBD sits at the family root, one node above the Proteobacteria clade PTN002215342 that holds every T2SS-named leaf, and the PilV/MshD proteins receiving the IBA are grafted non-reference members rather than tree leaves; flagged to GO Central. Supporting Evidence: PMID:30346996 The supernatant of the xcpV mutant, containing secreted proteins, displayed the lowest LasB activity, suggesting that the secretion of LasB was significantly compromised. file:PSEAE/xcpV/xcpV-bioinformatics/RESULTS.md The real fault is narrower: the IBD sits one node above PTN002215342 (Proteobacteria, 10 leaves), which holds every T2SS-named leaf including XcpV, while the root also covers two deep generic prepilins. |
| GO:0015628 protein secretion by the type II secretion system | IDA PMID:9818381 GSP-dependent protein secretion in gram-negative bacteria: t... | ACCEPT | Summary: PseudoCAP IDA citing Filloux, Michel and Bally 1998, a review of the Xcp system; sole seed of the GO:0015628 IBD at PTN002446181. Reason: The term is correct (xcpV mutants lose secretion; PMID:1309616, PMID:30346996), but a review with no original secretion data (full text checked) cannot support IDA. The evidence should be TAS for this reference, or the row should be re-keyed to a primary mutant paper (PMID:30346996 or PMID:1309616) as IMP. Recorded consistently with the same defect on XcpX, XcpS and XcpW. Supporting Evidence: PMID:9818381 we will use the P. aeruginosa Xcp system as a basis to discuss multiple aspects of the GSP mechanism PMID:30346996 The absence of either XcpV or -W resulted in the non-functional T2SS |
| GO:0015628 protein secretion by the type II secretion system | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the GspI entries IPR003413 and IPR010052. Reason: Correct for a T2SS-specific family; consistent with the mutant evidence for XcpV. Supporting Evidence: PMID:30346996 The absence of either XcpV or -W resulted in the non-functional T2SS |
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Download this section (compressed HTML)Q: Does PTN002446181 (PTHR38779) contain both T2SS GspI and type IV pilus PilV proteins, and if so should its T2SS IBDs move to a GspI-only descendant node?
Q: Does the full text of PMID:8331069 contain any assay of XcpV complex membership, or should the PseudoCAP GO:0015627 row be re-keyed to PMID:19828448?
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