hutI (PA5092) encodes imidazolonepropionase (imidazolone-5-propionate hydrolase, EC 3.5.2.7) of Pseudomonas aeruginosa. It is a cytoplasmic member of the metallo-dependent (amidohydrolase) hydrolase superfamily, HutI family, with a TIM-barrel catalytic domain that binds one zinc or iron ion. It catalyses the third step of the universal histidine utilization (hut) pathway: hydrolytic ring opening of 4-imidazolone-5-propanoate, the product of urocanase, to N-formimino-L-glutamate (FIGLU). In P. aeruginosa, FIGLU is then converted to glutamate by either the four-step (HutE) or the five-step (HutF/HutG) branch. hutI lies in the HutC-repressed, urocanate-inducible hutU-hutG operon, and histidine catabolism lets the bacterium use histidine as a carbon and nitrogen source. In P. aeruginosa itself, its function rests on homology, family signatures and operon context: no direct biochemical or genetic study of PA5092 has been reported.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005506 iron ion binding | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: UniRule (HAMAP MF_00372) transfer of the HutI cofactor annotation. The rule states that HutI binds one zinc or iron ion per subunit at a conserved His/Asp metal site. Reason: Plausible cofactor binding, consistent with the conserved HAMAP metal ligands. The B. subtilis structure contains zinc; iron is the alternative metal the rule allows. Metal binding is part of how the enzyme works, not its function, so it is kept as non-core. Supporting Evidence: file:PSEAE/hutI/hutI-uniprot.txt Binds 1 zinc or iron ion per subunit. |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: HAMAP/InterPro cytoplasm location. HutI has no signal peptide or transmembrane segment and acts on an intracellular pathway intermediate. Reason: Histidine catabolism after uptake is cytoplasmic. The soluble HutI family is cytoplasmic, and this is where the core activity takes place. Supporting Evidence: file:PSEAE/hutI/hutI-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0006548 L-histidine catabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PAINT node PTN000505272 (PTHR42752, LUCA-level node over bacterial HutI and eukaryotic AMDHD1). Its IBD is seeded only by this gene's own PseudoCAP IMP row. The target appearing in its own WITH/FROM is expected, not circular. Reason: HutI performs step III of histidine degradation, so the enzyme itself does part of the work of this process. The node placement suits a universal-pathway enzyme family, and PA5092 is a canonical member (HAMAP MF_00372, TIGR01224) in the PAO1 hut operon. The process term covers the shared upstream steps of both FIGLU branches that P. aeruginosa possesses, so it is the appropriate level for this enzyme. The seed reference itself does not visibly support the claim (see the IMP row); the claim is accepted on the independent evidence below. Supporting Evidence: PMID:16475788 The first three steps for the degradation of histidine include the action of HutH, HutU, and HutI to convert L-histidine to N-formimino-L-glutamate. PMID:17717196 are common to both the four-step and the five-step pathways file:PSEAE/hutI/hutI-uniprot.txt It is the third step in the universal histidine degradation pathway. |
| GO:0006548 L-histidine catabolic process | IEA GO_REF:0000120 | ACCEPT | Summary: HAMAP/InterPro (HutI family) mapping to L-histidine catabolic process. Reason: Same correct claim as the IBA row, from the HutI family signature. Supporting Evidence: file:PSEAE/hutI/hutI-uniprot.txt Belongs to the metallo-dependent hydrolases superfamily. HutI family. |
| GO:0006548 L-histidine catabolic process | IMP PMID:4290562 Formation and operation of the histidine-degrading pathway i... | ACCEPT | Summary: PseudoCAP IMP; sole seed of the PTN000505272 L-histidine catabolic process IBD (52 leaf IBAs, 50 taxa). Lessie and Neidhardt (1967) studied induction and repression of the P. aeruginosa histidine-degrading enzymes using urocanase-deficient, auxotrophic and repression mutants. Reason: The claim is correct, and it is accepted on independent evidence (HutI catalyses step III; HAMAP family; hut operon). The abstract of the cited paper does not visibly support it for this gene, though. It names the activities studied as steps I, II and IV (histidase, urocanase, FIGLU degradation), mentions neither step III nor a step III mutant, and in 1967 no mutation could be assigned to PA5092. The full text (supplied by the user, read 2026-11-05) confirms that step III is never assayed and that there is no hutI mutant, so the reference does not support the row. Supporting Evidence: PMID:4290562 Histidine ammonia lyase (histidase), urocanase, and the capacity to degrade formiminoglutamate, which are respectively involved in steps I, II, and IV in the catabolism of histidine PMID:16475788 The first three steps for the degradation of histidine include the action of HutH, HutU, and HutI to convert L-histidine to N-formimino-L-glutamate. |
| GO:0008270 zinc ion binding | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: UniRule (HAMAP MF_00372) cofactor annotation. The B. subtilis HutI structure has a zinc ion bound in the TIM-barrel active site. Reason: Well supported by the conserved metal ligands and homolog structures. It is a catalytic cofactor rather than the enzyme's function, so it is kept as non-core. Supporting Evidence: PMID:16990261 X-ray fluorescence scan analysis confirmed that the bound metal ion was a zinc ion. file:PSEAE/hutI/hutI-uniprot.txt Binds 1 zinc or iron ion per subunit. |
| GO:0016787 hydrolase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO from the amidohydrolase-related domain (IPR006680). Reason: Correct but too general. The specific activity, imidazolonepropionase activity (GO:0050480), is an is_a descendant that the gene already carries from IBA and IEA rows. Proposed replacements: imidazolonepropionase activity Supporting Evidence: file:PSEAE/hutI/hutI-uniprot.txt Catalyzes the hydrolytic cleavage of the carbon-nitrogen bond in imidazolone-5-propanoate to yield N-formimidoyl-L-glutamate. |
| GO:0016810 hydrolase activity, acting on carbon-nitrogen (but not peptide) bonds | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO from the metal-dependent hydrolase composite domain (IPR011059). Reason: Correct but general. The specific activity, imidazolonepropionase activity (GO:0050480), is an is_a descendant already carried by the gene. Proposed replacements: imidazolonepropionase activity Supporting Evidence: file:PSEAE/hutI/hutI-uniprot.txt Catalyzes the hydrolytic cleavage of the carbon-nitrogen bond in imidazolone-5-propanoate to yield N-formimidoyl-L-glutamate. |
| GO:0016812 hydrolase activity, acting on carbon-nitrogen (but not peptide) bonds, in cyclic amides | IEA GO_REF:0000120 | MODIFY | Summary: Combined IEA (ARBA and the HutI InterPro entry): cyclic-amide C-N hydrolase. This is the direct parent of imidazolonepropionase activity. Reason: Correct (the substrate's imidazolone ring is a cyclic amide) but general. It should be replaced by the specific is_a child, imidazolonepropionase activity (GO:0050480), which the gene already carries. Proposed replacements: imidazolonepropionase activity Supporting Evidence: PMID:16990261 hydrolyzing the carbon-nitrogen bonds in 4-imidazolone-5-propionic acid to yield N-formimino-l-glutamic acid |
| GO:0050480 imidazolonepropionase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN000505272, a LUCA-level node over bacterial HutI and eukaryotic AMDHD1. Its IBD is seeded only by this gene's PseudoCAP IMP row, so the 52 leaf IBAs (including human and rodent AMDHD1) all rest on that seed. Reason: PA5092 is a canonical HutI (HAMAP MF_00372, TIGR01224, conserved metal and substrate-binding residues) encoded in the hut operon, so it sits squarely inside the clade whose function this is. The node term suits a universally conserved pathway enzyme family. The seed reference does not visibly measure step III (see the IMP row), so the IBD needs a better anchor. Its conclusion is still correct, and the IBA is accepted on independent grounds. Supporting Evidence: file:PSEAE/hutI/hutI-uniprot.txt Catalyzes the hydrolytic cleavage of the carbon-nitrogen bond in imidazolone-5-propanoate to yield N-formimidoyl-L-glutamate. PMID:16990261 Imidazolonepropionase (EC 3.5.2.7) catalyzes the third step in the universal histidine degradation pathway |
| GO:0050480 imidazolonepropionase activity | IEA GO_REF:0000120 | ACCEPT | Summary: HAMAP/EC/Rhea-based imidazolonepropionase activity. Reason: Same correct claim as the IBA row, from the curated HAMAP family rule and its EC/Rhea reaction. Supporting Evidence: file:PSEAE/hutI/hutI-uniprot.txt Catalyzes the hydrolytic cleavage of the carbon-nitrogen bond in imidazolone-5-propanoate to yield N-formimidoyl-L-glutamate. |
| GO:0050480 imidazolonepropionase activity | IMP PMID:4290562 Formation and operation of the histidine-degrading pathway i... | ACCEPT | Summary: PseudoCAP IMP; sole seed of the PTN000505272 imidazolonepropionase activity IBD (52 leaf IBAs). Annotated from Lessie and Neidhardt 1967, a regulatory and biochemical study of the P. aeruginosa hut enzymes. Reason: The activity is accepted on independent family and structural evidence, but the abstract of the cited paper does not visibly support it as an IMP for this gene. It lists the activities studied as histidase, urocanase and FIGLU degradation (steps I, II, IV). Imidazolonepropionase (step III) is not mentioned, no step III mutant appears in the abstract, and a 1967 mutant could not be mapped to PA5092. An enzyme assay of mutant extracts could support an activity if the paper tied it to the gene, but nothing visible here assays this activity at all. The full text (read 2026-11-05) confirms that no imidazolonepropionase assay and no hutI mutant appear in the paper, so the reference does not support the row. Supporting Evidence: PMID:4290562 Histidine ammonia lyase (histidase), urocanase, and the capacity to degrade formiminoglutamate, which are respectively involved in steps I, II, and IV in the catabolism of histidine PMID:16990261 Imidazolonepropionase (EC 3.5.2.7) catalyzes the third step in the universal histidine degradation pathway |
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Download this section (compressed HTML)Q: Does the full text of Lessie and Neidhardt 1967 (PMID:4290562) report any imidazolonepropionase (step III) measurement or step III mutant? If not, the PseudoCAP IMP rows on PA5092, the sole seeds of the PTN000505272 IBDs, should be re-keyed or withdrawn.
Q: Is there an experimentally characterized HutI or AMDHD1 (enzyme assay or genetically defined mutant) that PAINT could use to re-anchor PTN000505272?
Experiment: Construct a clean PAO1 hutI (PA5092) deletion, test growth on histidine and on urocanate as sole carbon and nitrogen source, and measure accumulation of imidazolonepropionate or its breakdown products, with complementation. In parallel, assay purified PA5092 for imidazolonepropionase activity and metal dependence (Zn versus Fe).
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