hpd (PP_3433) encodes 4-hydroxyphenylpyruvate dioxygenase (HPPD; EC 1.13.11.27), a cytoplasmic non-heme Fe(II)-dependent oxygenase of the 4HPPD (VOC superfamily) family. It catalyzes the conversion of 4-hydroxyphenylpyruvate to homogentisate, coupling oxidative decarboxylation, aromatic hydroxylation, and a 1,2-side-chain migration in a single reaction that consumes molecular oxygen. This is the committed, gateway step of the homogentisate central catabolic pathway, through which Pseudomonas putida degrades L-tyrosine, L-phenylalanine, and 3-hydroxyphenylacetate to the central metabolites fumarate and acetoacetate. Loss of hpd abolishes growth on tyrosine or phenylalanine as sole carbon source, confirming its essential role in routing aromatic amino acids into central metabolism.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003868 4-hydroxyphenylpyruvate dioxygenase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Core molecular function. Q88HC7 belongs to the 4HPPD family (TIGR01263, IPR005956, PANTHER PTHR11959:SF1) and carries the conserved His/His/Glu Fe(II)-binding triad (residues 162, 241, 323). The HPPD function is strongly supported in P. putida by genetics, proteomics and RB-TnSeq fitness data (see hpd-deep-research-falcon.md; PMID:15262943). Reason: Directly supported by family/domain assignment and by experimental evidence that hpd is required for growth on tyrosine/phenylalanine via the homogentisate pathway in P. putida. |
| GO:0006572 L-tyrosine catabolic process | IEA GO_REF:0000118 | ACCEPT | Summary: HPPD performs the gateway step (4-HPP to homogentisate) of the homogentisate pathway, the route by which P. putida degrades L-tyrosine. hpd mutants cannot grow on tyrosine as sole carbon source. Reason: Accurate biological process; well supported by the homogentisate pathway literature in P. putida. |
| GO:0009072 aromatic amino acid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: Correct but more general than the specific catabolic role. The homogentisate pathway degrades both tyrosine and phenylalanine, so an aromatic-amino-acid-level term is defensible, but the more informative term is the catabolic process. Reason: The annotation is correct but the generic metabolic term under-specifies the function. Replace with the catabolic process term, which captures the documented degradative role. Proposed replacements: aromatic amino acid catabolic process |
| GO:0016701 oxidoreductase activity, acting on single donors with incorporation of molecular oxygen | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: This is a high-level parent of the specific 4-hydroxyphenylpyruvate dioxygenase activity (GO:0003868), which is already annotated. It is not wrong but is redundant and uninformative given the specific child term. Reason: Grouping/parent term subsumed by the specific GO:0003868 annotation; retained for completeness but adds no specific functional information. |
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