PilA (PA4525) is the major pilin of the type IVa pilus of Pseudomonas aeruginosa. It is made as a prepilin with a short positively charged leader that the prepilin peptidase PilD cleaves before N-methylating the new N-terminal phenylalanine. Unassembled pilin sits in the inner membrane, anchored by its hydrophobic N-terminal helix; there it also binds the sensor kinase PilS and so represses its own transcription when pilin is abundant. The assembly machine polymerises PilA from this pool into a helical fibre in which the N-terminal helices pack into the hydrophobic core and the C-terminal globular domains, closed by a disulfide loop, coat the surface. Repeated extension and PilT/PilU-driven retraction of PilA fibres powers twitching motility, and the fibres mediate attachment to host cells and abiotic surfaces, biofilm architecture and infection by pilus-specific phages. Loss of PilA abolishes surface pili and twitching.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005829 cytosol | IDA PMID:25049409 A phage protein that inhibits the bacterial ATPase required ... | UNDECIDED | Summary: CACAO IDA from Chung et al. 2014 (phage Tip protein inhibits PilB), with part_of cytosol. Full text could not be retrieved. Reason: The paper is about PilB inhibition and loss of surface piliation; the abstract reports no PilA fractionation, and the full text is not available here. The claim is also biologically doubtful: unassembled PilA is an inner-membrane protein anchored by its N-terminal hydrophobic helix (UniProt; PMID:27162347), not a soluble cytosolic protein, so a cellular (non-surface) PilA pool in a Western blot may have been recorded as cytosol. Left undecided because the figure behind the row cannot be checked. Supporting Evidence: PMID:27162347 We suggest that direct interactions between PilA and PilS in the inner membrane reduce pilA transcription when PilA levels are high. |
| GO:0005886 plasma membrane | EXP PMID:27162347 Type IV pilins regulate their own expression via direct intr... | ACCEPT | Summary: UniProt EXP from Kilmury and Burrows 2016: the unassembled PilA pool interacts with PilS within the inner membrane. Reason: The inner membrane is where pilin waits for assembly and where it acts as the autoregulatory signal to PilS. Correct location of the unassembled pool, alongside the fibre location. Supporting Evidence: PMID:27162347 We suggest that direct interactions between PilA and PilS in the inner membrane reduce pilA transcription when PilA levels are high. |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (cell inner membrane) to plasma membrane. Reason: Same claim as the EXP row, which is experimentally supported. Supporting Evidence: PMID:27162347 We suggest that direct interactions between PilA and PilS in the inner membrane reduce pilA transcription when PilA levels are high. |
| GO:0007155 cell adhesion | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from IPR001082 (pilin). Reason: Type IV pili are adhesins and PilA is the fibre subunit whose globular domain forms the surface that contacts the environment; pilA mutants are reduced in association with host epithelial cells and in surface attachment. Adhesion is one of the core roles of the pilus. Supporting Evidence: PMID:12933890 As expected, the pilA mutant demonstrated reduced association and invasion of corneal epithelial cells PMID:39666767 surrounded by the C-terminal globular domain of PilA that coats the outer surface of the pilus, mediating interactions with the surrounding environment |
| GO:0009289 pilus | EXP PMID:39666767 Structure of the Pseudomonas aeruginosa PAO1 Type IV pilus. | MODIFY | Summary: UniProt EXP from the 3.2 A cryo-EM structure of the native PAO1 type IV pilus. Reason: Correct but general. The structure is of a type IV pilus built of PilA, so the specific child GO:0044096 type IV pilus is supported; PilA already carries it (IDA, IBA). Proposed replacements: type IV pilus Supporting Evidence: PMID:39666767 PilA subunits constituting the T4P exhibit a classical pilin fold featuring an extended N-terminal Ξ±-helix linked to a C-terminal globular Ξ²-sheet-containing domain, which are packed tightly along the pilus |
| GO:0009289 pilus | IDA PMID:2985436 Cloning and sequencing of the Pseudomonas aeruginosa PAK pil... | MODIFY | Summary: PseudoCAP IDA citing Pasloske et al. 1985, cloning and sequencing of the strain PAK pilin gene. Reason: The claim is right but general; the pilus is a type IV pilus (GO:0044096), which the same PseudoCAP paper row also asserts. The reference is a gene-sequencing paper on the strain PAK orthologue whose abstract shows no location assay; the location is directly shown for PAO1 PilA by PMID:39666767. Proposed replacements: type IV pilus Supporting Evidence: PMID:39666767 Here, we report a 3.2 Γ
-resolution structure of the P. aeruginosa PAO1 T4P determined by electron cryomicroscopy (cryo-EM). |
| GO:0009289 pilus | IEA GO_REF:0000120 | MODIFY | Summary: Combined IEA (pilin InterPro domain and UniProt Fimbrium location) to pilus. Reason: Correct but general; PilA is the major subunit of a type IV pilus, the specific term it already carries. Proposed replacements: type IV pilus Supporting Evidence: file:PSEAE/pilA/pilA-uniprot.txt Fimbrium {ECO:0000269|PubMed:39666767} |
| GO:0009986 cell surface | IDA PMID:25049409 A phage protein that inhibits the bacterial ATPase required ... | MODIFY | Summary: CACAO IDA from Chung et al. 2014: surface piliation (surface PilA) is lost on Tip expression. Reason: Surface PilA is pilin in the extracellular pilus fibre, which is what a surface-piliation assay measures. Cell surface is true but less informative than GO:0044096 type IV pilus, which PilA already carries. Proposed replacements: type IV pilus Supporting Evidence: PMID:25049409 Tip expression results in the loss of surface piliation. |
| GO:0043107 type IV pilus-dependent motility | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN002013003, sole seed the PseudoCAP rows on this protein; PilA in its own WITH/FROM is expected for a seed. Reason: Correct for PilA, the fibre subunit whose extension and retraction drives twitching. The node holds 10 major pilins of PTHR30093:SF34, and PAINT curators have already added NOT IRDs at two divergent sub-nodes. Some remaining leaves (E. coli K-12 PpdD, H. influenzae PpdD homologue) come from species without documented twitching, a mild over-reach of the node noted in the notes but not one that affects this gene. Supporting Evidence: PMID:12933890 The pilA mutant is twitching motility negative because it lacks pili |
| GO:0043107 type IV pilus-dependent motility | IDA PMID:12933890 Twitching motility contributes to the role of pili in cornea... | ACCEPT | Summary: PseudoCAP IDA citing Zolfaghar et al. 2003, which used a non-piliated pilA mutant of strain PAK as a twitching-negative control. Reason: The claim is correct and central: PilA is the structural subunit of the fibre that powers twitching, so it does the work of the process. The evidence in the paper is a mutant colony-morphology assay in strain PAK, which is IMP rather than IDA. Seed of the PTN002013003 motility IBD. Supporting Evidence: PMID:12933890 The pilA mutant is twitching motility negative because it lacks pili and thus was used as a control to distinguish the contributions of pili and their twitching motility function. |
| GO:0043107 type IV pilus-dependent motility | IMP PMID:9224878 Genes involved in the biogenesis and function of type-4 fimb... | ACCEPT | Summary: PseudoCAP IMP citing Alm and Mattick 1997, an overview of type 4 fimbrial biogenesis genes in P. aeruginosa that includes a pilA mutant twitching assay (Fig. 1). Reason: The claim is correct and IMP is supported. The paper (Gene 192:89-98, full text supplied by the user and read 2026-11-05) is largely an overview of the laboratory's type 4 fimbrial work, but its Fig. 1 is a stab-inoculation twitching assay showing that the wild-type PAK strain spreads at the agar-plate interface while a pilA mutant does not move. That is a mutant phenotype for this term. Seed of the PTN002013003 motility IBD together with the PMID:12933890 row. Supporting Evidence: PMID:9224878 Type-4 fimbriae mediate attachment to host epithelial tissues and a form of surface translocation called twitching motility. |
| GO:0043709 cell adhesion involved in single-species biofilm formation | IMP PMID:16849183 Surface plasmon resonance shows that type IV pili are import... | KEEP AS NON CORE | Summary: PseudoCAP IMP: SPR shows that a pilA mutant is defective in attachment to a gold surface. Reason: PilA fibres do mediate attachment, and the assay directly measures it for a pilA mutant. The biofilm-specific framing is a context on top of the core adhesion role, so it is kept as non-core. Supporting Evidence: PMID:16849183 Both mutants lacking pili (pilA), and those possessing an overabundance of pili (pilT), showed reduced SPR measured attachment compared with the wild-type PAO1 strain. |
| GO:0044011 single-species biofilm formation on inanimate substrate | IMP PMID:14507363 Involvement of bacterial migration in the development of com... | KEEP AS NON CORE | Summary: PseudoCAP IMP: time-lapse confocal microscopy with motility mutants shows that mushroom caps form by type IV pilus-driven migration. Reason: Pilus-driven migration contributes to biofilm architecture; PilA does this work as the fibre subunit, but biofilm development is a downstream context of twitching rather than a core function. Supporting Evidence: PMID:14507363 The migrating bacteria form the mushroom caps by climbing the stalks and aggregating on the tops in a process which is driven by type-IV pili. |
| GO:0044096 type IV pilus | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN002013003, sole seed the PseudoCAP IDA on this protein. Reason: PilA is the major subunit of the type IV pilus, and every leaf of the node is a type IV major pilin (PTHR30093:SF34), so the location is sound for the clade. Supporting Evidence: PMID:39666767 The N-terminal helices constitute the pilus core where they stabilise the tubular assembly via hydrophobic interactions. |
| GO:0044096 type IV pilus | IDA PMID:2985436 Cloning and sequencing of the Pseudomonas aeruginosa PAK pil... | ACCEPT | Summary: PseudoCAP IDA citing Pasloske et al. 1985 (cloning and sequencing of the strain PAK pilin gene). Reason: Core location; PilA is the structural subunit of the fibre, shown directly for PAO1 by cryo-EM (PMID:39666767). The cited paper is abstract-only here, concerns the strain PAK orthologue and its abstract describes only gene cloning and sequencing; the curator may have used the comparison with purified pilus protein in the full text. Accepted on the strength of the claim. Seed of the PTN002013003 type IV pilus IBD. Supporting Evidence: PMID:39666767 PilA subunits constituting the T4P exhibit a classical pilin fold |
| GO:0044167 host cell endoplasmic reticulum membrane | EXP PMID:23266901 Type IV pilus protein PilA of Pseudomonas aeruginosa modulat... | MARK AS OVER ANNOTATED | Summary: UniProt EXP from Okuda et al. 2013: PilA binds the host ER membrane protein CAMLG in a yeast two-hybrid screen and, when the pilA gene is over-expressed inside BEAS-2B cells, raises cytoplasmic Ca2+. Reason: The host ER location rests on PilA expressed inside human cells from a transfected gene and on two-hybrid binding to an ER membrane protein, not on PilA delivered by bacteria during infection. PilA is a secreted fibre subunit and no route for it into the host ER is known, so this is at most a peripheral, unconfirmed observation. Supporting Evidence: PMID:23266901 Overexpression of the pilA gene in BEAS-2B cells resulted in a significant increase in cytoplasmic Ca(2+) |
| GO:0044167 host cell endoplasmic reticulum membrane | IEA GO_REF:0000044 | MARK AS OVER ANNOTATED | Summary: UniProt subcellular-location mapping (host ER membrane) from the same paper. Reason: Same claim as the EXP row, consistent with it; based on heterologous expression of PilA inside host cells. Supporting Evidence: PMID:23266901 Using a yeast two-hybrid screen, we showed that the calcium-modulating cyclophilin ligand (CAMLG), which is involved in Ca(2+) signaling, was the major host cell PilA binding protein. |
| GO:0050848 regulation of calcium-mediated signaling | IMP PMID:23266901 Type IV pilus protein PilA of Pseudomonas aeruginosa modulat... | MARK AS OVER ANNOTATED | Summary: PseudoCAP IMP: infection with a delta-pilA strain, unlike wild type, does not raise intracellular Ca2+ in BEAS-2B cells. Reason: The process is in the host, and the delta-pilA strain lacks pili altogether, so loss of the Ca2+ response may reflect loss of pilus-mediated attachment and invasion rather than a PilA-CAMLG signalling activity. The direct mechanism rests on intracellular over-expression. A peripheral and indirect claim for a structural pilin. Supporting Evidence: PMID:23266901 Infection of BEAS-2B cells with the P. aeruginosa wild-type strain, but not with the pilA gene knockout strain (ΞpilA), caused a significant increase in intracellular Ca(2+) concentration in infected cells. |
Loading supporting contentβ¦
Download this section (compressed HTML)Q: Does PilA reach the host cell interior during infection, and if so how, given that the CAMLG/host-ER evidence comes from expressing pilA inside host cells?
Experiment: Infect BEAS-2B cells with strains expressing PilA variants that assemble pili but carry point mutations abolishing CAMLG binding, to separate a PilA-CAMLG signalling activity from pilus-mediated attachment in the Ca2+ response.
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)