FimU (PA4550) is a minor pilin of the type IVa pilus of Pseudomonas aeruginosa. Like the major pilin it is made as a prepilin with a short class III leader that the prepilin peptidase PilD removes, followed by a hydrophobic N-terminal helix that anchors it in the inner membrane before assembly. Its globular domain is structurally similar to the GspH minor pseudopilin of type II secretion systems despite little sequence identity. FimU is incorporated into pilus fibres independently of the other minor pilins and is thought to couple the PilV-PilW-PilX-PilY1 priming complex to the major pilin PilA; it is one of the key promoters of pilus assembly. fimU mutants make few or no surface pili and do not twitch, a defect that overexpression of the related minor pilin FimT can rescue.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping to plasma membrane; the UniProt location itself is ARBA-predicted. Reason: As a class III prepilin with an N-terminal hydrophobic helix, FimU is an inner-membrane protein before it is processed by PilD and incorporated into the pilus. The ARBA location is not evidence on its own, but the PilD processing shown experimentally and the Phobius TM helix agree with it. Supporting Evidence: PMID:20338182 the minor pilins FimU, PilV, PilW, PilX, and PilE were processed by the pre-pilin peptidase PilD file:PSEAE/fimU/fimU-uniprot.txt /evidence="ECO:0000256|SAM:Phobius" |
| GO:0009297 pilus assembly | IDA PMID:20338182 Pseudomonas aeruginosa minor pilins are incorporated into ty... | MODIFY | Summary: PseudoCAP IDA from Giltner et al. 2010: FimU and PilX are key promoters of pilus assembly. Reason: Correct but general. The pilus is a type IVa pilus, so the specific child GO:0043683 type IV pilus assembly applies; FimU already carries it (IMP, PMID:8682785). Proposed replacements: type IV pilus assembly Supporting Evidence: PMID:20338182 with FimU and PilX being implicated as key promoters of pilus assembly on the cell surface |
| GO:0015627 type II protein secretion system complex | IEA GO_REF:0000002 | REMOVE | Summary: InterPro2GO mapping from IPR022346 (T2SS GspH). Reason: FimU shares the GspH fold, but it is the type IV pilus minor pilin, not a T2SS component. P. aeruginosa encodes a separate Xcp GspH, XcpU (PA3100, Q00515). The pilus minor pilins are assembled into type IV pili; what the literature shows is T2S minor pseudopilins substituting in T4P assembly, not FimU acting in T2S. The domain-to-complex mapping is wrong for this family member. Supporting Evidence: PMID:25389296 our 1.4 Å crystal structure of FimU revealed striking architectural similarity to its T2S ortholog GspH, despite minimal sequence identity PMID:25389296 FimU is incorporated independently of the others and is proposed to couple the putative minor pilin-PilY1 complex to the major subunit. |
| GO:0015628 protein secretion by the type II secretion system | IEA GO_REF:0000002 | REMOVE | Summary: InterPro2GO mapping from IPR022346 (T2SS GspH). Reason: Same over-reach as the complex row: there is no evidence that FimU contributes to Xcp secretion, and the operon and all experimental data place it in type IV pilus assembly. The Xcp system has its own GspH, XcpU. Supporting Evidence: PMID:8682785 Isogenic mutants constructed by allelic exchange demonstrated that the fimU gene was required for fimbrial biogenesis and twitching motility |
| GO:0043107 type IV pilus-dependent motility | IMP PMID:20338182 Pseudomonas aeruginosa minor pilins are incorporated into ty... | ACCEPT | Summary: PseudoCAP IMP: loss or overexpression of any minor pilin, FimU included, impairs twitching. Reason: FimU is a structural component of the pilus fibre, so it does part of the work of pilus-driven motility. Mutant phenotype confirmed by PMID:8682785. Supporting Evidence: PMID:20338182 Maintenance of a specific stoichiometric ratio among the minor pilins was important for function, as loss or overexpression of any component impaired motility. |
| GO:0043683 type IV pilus assembly | IMP PMID:8682785 Identification of two genes with prepilin-like leader sequen... | ACCEPT | Summary: PseudoCAP IMP from Alm and Mattick 1996: the fimU allelic exchange mutant lacks fimbriae. Reason: Core process. FimU is a minor pilin that helps prime and couple pilus assembly to the major subunit. Supporting Evidence: PMID:8682785 Isogenic mutants constructed by allelic exchange demonstrated that the fimU gene was required for fimbrial biogenesis and twitching motility PMID:25389296 FimU is incorporated independently of the others and is proposed to couple the putative minor pilin-PilY1 complex to the major subunit. |
| GO:0044096 type IV pilus | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA from PTN008624060, sole seed the PseudoCAP IDA on this protein; FimU in its own WITH/FROM is expected for a seed. Reason: The seed is sound, and the node's seven leaves (Shewanella FimU, Xanthomonas FimT x2, Neisseria, Vibrio and Dictyoglomus minor pilins) are all FimU/FimT-type minor pilins, a class incorporated into type IV pili. Supporting Evidence: PMID:20338182 This is the first study to demonstrate that the minor pilins, conserved among bacteria expressing type IVa pili, are incorporated into the fiber |
| GO:0044096 type IV pilus | IDA PMID:20338182 Pseudomonas aeruginosa minor pilins are incorporated into ty... | ACCEPT | Summary: PseudoCAP IDA from Giltner et al. 2010: specific antibodies detect FimU throughout sheared pilus filaments. Reason: Direct detection of the protein in the pilus fibre in P. aeruginosa, confirmed by Nguyen et al. 2015. Core location. Sole seed of the PTN008624060 type IV pilus IBD. Supporting Evidence: PMID:20338182 Using specific antibodies for each protein, we showed that the minor pilins FimU, PilV, PilW, PilX, and PilE were processed by the pre-pilin peptidase PilD and incorporated throughout the growing pilus filament. PMID:25389296 FimU is incorporated independently of the others |
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Download this section (compressed HTML)Q: Is FimU located at the pilus tip with the PilVWXY1 priming complex, or distributed along the fibre as the antibody data of Giltner et al. 2010 suggest?
Experiment: Map FimU position in purified pili by immunogold or cryo-electron tomography of tagged FimU, in wild type and in pilVWX deletion strains, to test the proposed coupling role between the priming complex and PilA.
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