XcpS (PA3102) is the GspF-family inner-membrane platform protein 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 a polytopic cytoplasmic-membrane protein with three transmembrane segments and a large cytoplasmic N-terminal domain. XcpS forms the inner-membrane assembly platform with XcpY (GspL) and XcpZ (GspM) and binds the secretion ATPase XcpR (GspE), which stabilises it, coupling ATP hydrolysis to pseudopilus assembly. It is related to the PilC platform protein of type IV pili and localises the Xcp machinery to the cell poles.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN000768597, seeded by E. coli HofC and GspF. Reason: Not a PseudoCAP-seeded IBD. GspF/PilC-family platform proteins are integral inner-membrane proteins, and the XcpS topology in the inner membrane was mapped experimentally, so the inherited plasma membrane location holds for XcpS. Supporting Evidence: PMID:17464073 One of the core components of the Xcp system is the inner-membrane protein XcpS (GspF) file:PSEAE/xcpS/xcpS-uniprot.txt TOPO_DOM 190..219 FT /note="Periplasmic" FT /evidence="ECO:0000269|PubMed:17464073" |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (cell inner membrane) to plasma membrane. Reason: XcpS is a multi-pass inner (cytoplasmic) membrane protein; in a Gram-negative bacterium the inner membrane is the plasma membrane. Supporting Evidence: PMID:17464073 One of the core components of the Xcp system is the inner-membrane protein XcpS (GspF) |
| GO:0009306 protein secretion | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the GspF/PilC conserved-site entry IPR001992 to protein secretion. Reason: Correct but general. The specific supported term is GO:0015628 protein secretion by the type II secretion system, which the gene already carries (IBA, IEA and PseudoCAP rows). Proposed replacements: protein secretion by the type II secretion system Supporting Evidence: PMID:17464073 Most exoproteins are exported by the type II secretion machinery, the Xcp system, which encompasses 12 different proteins. One of the core components of the Xcp system is the inner-membrane protein XcpS (GspF) |
| GO:0015627 type II protein secretion system complex | IDA PMID:16168578 Subcomplexes from the Xcp secretion system of Pseudomonas ae... | ACCEPT | Summary: PseudoCAP IDA from Robert et al. 2005, who co-purified an XcpRSYZ subcomplex of the Xcp secreton under native conditions. Reason: Direct biochemical evidence that XcpS is a component of the Xcp T2SS (assembly platform with XcpR, XcpY and XcpZ). Consistent with the XcpS stabilisation by XcpR and XcpY (PMID:17464073). Supporting Evidence: PMID:16168578 This subcomplex was also found to interact with XcpR and XcpS to form a XcpRSYZ complex which was isolated under native conditions PMID:17464073 XcpS was shown to be stabilized by co-expression of the XcpR (GspE) and XcpY (GspL) components of the machinery, demonstrating an interaction between these three proteins |
| GO:0015627 type II protein secretion system complex | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the T2SS-specific GspF entry IPR011850 to the T2SS complex. Reason: IPR011850 (NCBIfam TIGR02120 GspF) is specific to T2SS GspF, distinguishing it from type IV pilus PilC; the mapping is correct and is confirmed by the IDA row. Supporting Evidence: PMID:16168578 This subcomplex was also found to interact with XcpR and XcpS to form a XcpRSYZ complex which was isolated under native conditions file:PSEAE/xcpS/xcpS-uniprot.txt NCBIfam; TIGR02120; GspF; 1. |
| GO:0015628 protein secretion by the type II secretion system | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN000768597, whose IBD for this term rests solely on the PseudoCAP IDA row for XcpS citing the review PMID:9818381. Reason: The biological claim holds for XcpS and for T2SS GspF proteins generally. The seed's evidence code is wrong (IDA on a review), but primary evidence that XcpS is a functional Xcp component exists (species-specific function of XcpS hybrids, PMID:17464073; functional tagged XcpS, PMID:18832308), so the IBD remains sound. Of about 911 leaves in current QuickGO, a handful are named PilC/HofC/MshG (type IV pilus or MSHA platforms of the same family), a minor over-propagation that does not affect XcpS. XcpS in its own WITH/FROM reflects its seed and is expected. Supporting Evidence: PMID:17464073 XcpS domains were identified that are important for species-specific functioning and thus represent putative interaction domains file:PSEAE/xcpV/xcpV-bioinformatics/RESULTS.md PTN000768597 GO:0015628 (XcpS/GspF seed): 911 proteins; T2SS-named=846, T4P/MSHA/TCP-named=7, generic/other=58 |
| 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 PTN000768597 IBD for this term. Reason: The term is correct (XcpS is a core inner-membrane component of the Xcp secreton), 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 paper (for example PMID:17464073, functional analysis of XcpS hybrids, as IMP or IGI). Recorded consistently with the same defect on XcpX, XcpV 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:17464073 XcpS domains were identified that are important for species-specific functioning and thus represent putative interaction domains |
| GO:0015628 protein secretion by the type II secretion system | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the T2SS-specific GspF entry IPR011850. Reason: Correct for a T2SS-specific GspF family signature; consistent with the IBA and the experimental evidence for XcpS. Supporting Evidence: file:PSEAE/xcpS/xcpS-uniprot.txt InterPro; IPR011850; T2SS_GspF. PMID:17464073 One of the core components of the Xcp system is the inner-membrane protein XcpS (GspF) |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from IPR001992 to membrane. Reason: Correct but general; XcpS is an inner (plasma) membrane protein, and the gene already carries GO:0005886 plasma membrane. Proposed replacements: plasma membrane Supporting Evidence: PMID:17464073 the inner-membrane protein XcpS (GspF) |
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Q: Does XcpS bind calcium in its cytoplasmic domain as UniProt infers by similarity to P45780 (Ca2+ sites 97, 151, 155), and is this needed for platform function?
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