PA4022 (HdhA) is an NAD-preferring aldehyde/hydrazone dehydrogenase of Pseudomonas aeruginosa PAO1. It oxidizes acetaldehyde to acetate and catalyzes oxidative cleavage of hydrazone C=N bonds to the corresponding hydrazides and carboxylic acids. Native HdhA is dimeric. The gene starts the PA4022-eat-eutBC operon, induced through the acetaldehyde-responsive regulator EatR and RpoN, and contributes to ethanolamine utilization as a carbon source. HdhA and the closely related ExaC (PA1984) can compensate for one another during ethanol utilization. Hydrazone-dependent growth was reported with HdhA contributing more strongly than ExaC, but was not reproduced under the different conditions of a later study.
Definition: Catalysis of NAD+ or NADP+-dependent oxidative cleavage of a hydrazone carbon-nitrogen double bond to yield the corresponding hydrazide and carboxylic acid, with reduction of the nicotinamide cofactor.
Justification: Primary PA4022 assays establish oxidative hydrolysis of AEH and VEH, chemically distinct from aldehyde oxidation and simple hydrazone hydrolysis. Current QuickGO name searches found no corresponding hydrazone molecular-function term; no GO identifier is guessed. NAD+ is preferred by the measured enzyme, but NADP+ also supports activity.
Parent term: oxidoreductase activity
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004029 aldehyde dehydrogenase (NAD+) activity | IEA GO_REF:0000117 | MODIFY | Summary: PA4022 directly catalyzes NAD-dependent acetaldehyde oxidation. Reason: The broad parent is true, and primary PAO1 purification and recombinant-enzyme assays now establish substrate-specific chemistry. PMID22267508 identified native HdhA as PA4022 using distinguishing peptides, then measured acetaldehyde oxidation with NAD+ at pH 9.0. Refine this aldehyde-dehydrogenase parent to the supported acetaldehyde reaction. Hydrazone oxidative hydrolysis is represented separately because a hydrazone is not an aldehyde. Proposed replacements: acetaldehyde dehydrogenase (NAD+) activity Supporting Evidence: PMID:22267508 We found here that purified rHdhA and rExaC both oxidize acetaldehyde. |
| GO:0016491 oxidoreductase activity | IBA GO_REF:0000033 | MODIFY | Summary: PA4022 directly catalyzes NAD-dependent acetaldehyde oxidation and hydrazone oxidative hydrolysis. Reason: The broad parent is true, and primary PAO1 purification and recombinant-enzyme assays now establish substrate-specific chemistry. PMID22267508 identified native HdhA as PA4022 using distinguishing peptides, then measured acetaldehyde oxidation with NAD+ at pH 9.0. The generic oxidoreductase claim also encompasses demonstrated hydrazone oxidative hydrolysis; both specific activities are retained. PAINT loss checking found no IRD/IKR on this lineage; substrate specificity is supported by target experiments, not inferred across the entire AldB-like family. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000916590 SUPPORTS TRANSFER The existing ancestral oxidoreductase assignment remains biologically correct for PA4022; the gene is classified in PTHR43111:SF1 and direct target chemistry independently confirms redox activity. No IRD/IKR was reported by the lineage-loss check. MODIFY records target-specific refinement, not a false ancestral redox claim or family-wide substrate assignment. Proposed replacements: acetaldehyde dehydrogenase (NAD+) activity hydrazone dehydrogenase (NAD(P)+) activity Supporting Evidence: PMID:22267508 We found here that purified rHdhA and rExaC both oxidize acetaldehyde. PMID:22267508 The purified HDH converted AEH and NAD + to stoichiometric amounts of ADH, AMH, and acetate |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000002 | MODIFY | Summary: PA4022 directly catalyzes NAD-dependent acetaldehyde oxidation and hydrazone oxidative hydrolysis. Reason: The broad parent is true, and primary PAO1 purification and recombinant-enzyme assays now establish substrate-specific chemistry. PMID22267508 identified native HdhA as PA4022 using distinguishing peptides, then measured acetaldehyde oxidation with NAD+ at pH 9.0. The generic oxidoreductase claim also encompasses hydrazone oxidative hydrolysis; retain both specific activities rather than reducing the whole protein to one substrate. Proposed replacements: acetaldehyde dehydrogenase (NAD+) activity hydrazone dehydrogenase (NAD(P)+) activity Supporting Evidence: PMID:22267508 We found here that purified rHdhA and rExaC both oxidize acetaldehyde. PMID:22267508 The purified HDH converted AEH and NAD + to stoichiometric amounts of ADH, AMH, and acetate |
| GO:0140087 acetaldehyde dehydrogenase (NAD+) activity | IDA PMID:22267508 Group X aldehyde dehydrogenases of Pseudomonas aeruginosa PA... | NEW | Summary: Native PAO1 HdhA identity and recombinant PA4022 assays establish NAD-dependent acetaldehyde oxidation. Reason: The PR-authored ISS proposal is upgraded to direct evidence. Native PAO1 protein was identified as PA4022 by peptide mass fingerprinting and distinguishing peptides; the matched recombinant His-tagged HdhA oxidized acetaldehyde using NAD+ (pH 9.0). This establishes the GO:0140087 reaction without extrapolating cofactor specificity from ExaC. Native deletion/complementation supports participation in ethanolamine carbon utilization, not universal essentiality. The exact former ISS row is archived; the proposal is retained despite its now-redundant coverage by parent-row refinements to preserve provenance. Supporting Evidence: PMID:22267508 We found here that purified rHdhA and rExaC both oxidize acetaldehyde. PMID:22267508 Identity between the purified HDH and HdhA was confirmed by detecting peptides specific to HdhA tryptic peptides file:PSEAE/PA4022/PA4022-source-analysis/primary-assay-scope.yaml Deletion of the PA4022 gene reduced the growth of P. aeruginosa PAO1 on ethanolamine as a sole source of carbon |
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Download this section (compressed HTML)Q: Which culture, substrate-purity or strain differences explain the discordant hydrazone-supported growth results in 2012 and 2016?
Q: How do PA4022 and PA1984 partition acetaldehyde flux during ethanolamine versus ethanol utilization?
Experiment: Compare verified PAO1 wild type, PA4022 and exaC single mutants and the double mutant under both published culture regimes, using chemically verified AEH and VEH and measuring substrate disappearance, acetate production and growth. Include complementation to distinguish expression and pathway effects.
Hypothesis: Hydrazone growth depends on conditions that differ between the published studies.
Type: Controlled physiological replication and metabolite assay
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Download this section (compressed HTML)Generated by pairwise_exac.py (BLOSUM62 global alignment, open -10, extend -0.5).
| Pair | Lengths | Identity over aligned columns |
|---|---|---|
| Q9HX05 PA4022 (PAO1) vs Q9ZAA1 ExaC (ATCC 17933) | 506 / 506 | 98.2% |
| Q9HX05 PA4022 (PAO1) vs Q9I2C4 exaC/PA1984 (PAO1) | 506 / 506 | 98.4% |
| Q9ZAA1 ExaC (ATCC 17933) vs Q9I2C4 exaC/PA1984 (PAO1) | 506 / 506 | 99.4% |
Catalytic residues of ExaC mapped onto PA4022:
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