id: Q88GQ0
gene_symbol: katG
product_type: PROTEIN
aliases:
- PP_3668
status: COMPLETE
taxon:
  id: NCBITaxon:160488
  label: Pseudomonas putida (strain ATCC 47054 / DSM 6125 / CFBP 8728 / NCIMB 11950
    / KT2440)
description: >-
  katG encodes the bifunctional catalase-peroxidase (EC 1.11.1.21) of Pseudomonas
  putida KT2440, a soluble heme b-dependent hydroperoxidase. At a single heme active
  site it catalyzes two coupled reactions that detoxify hydrogen peroxide: a catalatic
  reaction dismutating H2O2 to water and oxygen (2 H2O2 -> O2 + 2 H2O), and a
  broad-spectrum peroxidatic reaction that reduces H2O2 to water using diverse organic
  electron donors (H2O2 + AH2 -> A + 2 H2O). The enzyme assembles as a homodimer or
  homotetramer and carries a covalent Trp-Tyr-Met crosslink that is required for the
  catalase but not the peroxidase activity. As a major H2O2-scavenging enzyme, KatG is
  a central component of the bacterial defense against oxidative stress.
existing_annotations:
- term:
    id: GO:0004096
    label: catalase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Catalase activity is one of the two core molecular functions of this bifunctional
      enzyme. UniProt records the catalatic reaction (2 H2O2 = O2 + 2 H2O) under EC
      1.11.1.21 and the FUNCTION line explicitly describes catalase activity.
    action: ACCEPT
    reason: >-
      The catalatic dismutation of hydrogen peroxide is a defining, well-supported core
      activity for a catalase-peroxidase and matches the UniProt catalytic-activity
      reaction and EC assignment.
    supported_by:
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Reaction=2 H2O2 = O2 + 2 H2O"
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Bifunctional enzyme with both catalase and broad-spectrum"
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "PTHR30555; HYDROPEROXIDASE I, BIFUNCTIONAL CATALASE-PEROXIDASE"
- term:
    id: GO:0004601
    label: peroxidase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Peroxidase activity is the second core molecular function of this bifunctional
      enzyme. UniProt records the peroxidatic reaction (H2O2 + AH2 = A + 2 H2O) and
      describes broad-spectrum peroxidase activity.
    action: ACCEPT
    reason: >-
      The broad-spectrum peroxidatic reduction of H2O2 using organic electron donors is
      a defining core activity of catalase-peroxidases and is directly supported by the
      UniProt catalytic-activity reaction.
    supported_by:
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Reaction=H2O2 + AH2 = A + 2 H2O"
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Bifunctional enzyme with both catalase and broad-spectrum"
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IEA
  original_reference_id: GO_REF:0000118
  qualifier: located_in
  review:
    summary: >-
      Cytosolic localization is a reasonable TreeGrafter prediction for a soluble
      bacterial catalase-peroxidase, but it is an IEA inference with no KT2440-specific
      localization evidence and is peripheral to the gene's core function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Catalase-peroxidases are typically soluble cytoplasmic enzymes, so the prediction
      is biologically plausible, but the annotation is electronic only and the cellular
      location is not the core defining feature of the gene.
    supported_by:
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Homodimer or homotetramer."
- term:
    id: GO:0006979
    label: response to oxidative stress
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: >-
      Response to oxidative stress is a core biological process for KatG: by scavenging
      hydrogen peroxide it directly protects the cell against oxidative damage.
    action: ACCEPT
    reason: >-
      H2O2 decomposition by catalase-peroxidase is a principal mechanism of defense
      against oxidative stress, consistent with the bifunctional H2O2-detoxifying
      activity recorded in UniProt.
    supported_by:
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Bifunctional enzyme with both catalase and broad-spectrum"
    - reference_id: file:PSEPK/katG/katG-notes.md
      supporting_text: >-
        central component of the cellular defense against oxidative/H2O2 stress.
- term:
    id: GO:0020037
    label: heme binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Heme b binding is mechanistically essential for this enzyme (UniProt records heme
      b as cofactor and an axial heme-iron binding residue), but as a cofactor-binding
      term it is broad relative to the specific catalase and peroxidase activity terms
      already present.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The annotation is correct and the heme is required for catalysis, but with the
      specific catalase and peroxidase molecular-function terms present, the generic
      heme-binding term adds little to the functional description and represents the
      cofactor-binding aspect rather than the core activity.
    supported_by:
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Name=heme b; Xref=ChEBI:CHEBI:60344"
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Binds 1 heme b (iron(II)-protoporphyrin IX) group per dimer."
- term:
    id: GO:0042744
    label: hydrogen peroxide catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000118
  qualifier: involved_in
  review:
    summary: >-
      Hydrogen peroxide catabolic process is the core biological process directly
      effected by both the catalase and peroxidase activities of KatG, which consume
      H2O2.
    action: ACCEPT
    reason: >-
      Both UniProt catalytic-activity reactions consume hydrogen peroxide, making H2O2
      catabolism the most direct process-level description of this enzyme's role.
    supported_by:
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Reaction=2 H2O2 = O2 + 2 H2O"
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Reaction=H2O2 + AH2 = A + 2 H2O"
- term:
    id: GO:0070301
    label: cellular response to hydrogen peroxide
  evidence_type: IEA
  original_reference_id: GO_REF:0000118
  qualifier: involved_in
  review:
    summary: >-
      Cellular response to hydrogen peroxide is consistent with KatG's role in
      decomposing H2O2 as part of the cell's defensive reaction to peroxide exposure;
      it is a valid but somewhat more peripheral process term than the direct H2O2
      catabolic process.
    action: KEEP_AS_NON_CORE
    reason: >-
      The annotation is biologically reasonable for an H2O2-scavenging enzyme, but the
      direct H2O2 catabolic process term more precisely captures the enzyme's core
      contribution; this response term is retained as non-core.
    supported_by:
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Bifunctional enzyme with both catalase and broad-spectrum"
- term:
    id: GO:0098869
    label: cellular oxidant detoxification
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: >-
      Cellular oxidant detoxification is correctly inferred from the catalase and
      peroxidase activities (the GOA entry derives it from GO:0004096 and GO:0004601),
      capturing the protective antioxidant role of KatG.
    action: KEEP_AS_NON_CORE
    reason: >-
      The term accurately describes the detoxification outcome of H2O2 decomposition but
      is more general than the specific hydrogen peroxide catabolic process term; it is
      retained as a valid non-core process annotation.
    supported_by:
    - reference_id: file:PSEPK/katG/katG-uniprot.txt
      supporting_text: "Bifunctional enzyme with both catalase and broad-spectrum"
    - reference_id: file:PSEPK/katG/katG-notes.md
      supporting_text: >-
        central component of the cellular defense against oxidative/H2O2 stress.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000118
  title: TreeGrafter-generated GO annotations
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: file:PSEPK/katG/katG-uniprot.txt
  title: UniProtKB Q88GQ0 KATG_PSEPK Pseudomonas putida KT2440
  findings:
  - statement: >-
      UniProt describes KatG as a bifunctional enzyme with both catalase and
      broad-spectrum peroxidase activity.
    supporting_text: "Bifunctional enzyme with both catalase and broad-spectrum"
  - statement: >-
      UniProt records the catalatic reaction dismutating hydrogen peroxide to oxygen and
      water.
    supporting_text: "Reaction=2 H2O2 = O2 + 2 H2O"
  - statement: >-
      UniProt records the peroxidatic reaction reducing hydrogen peroxide using an
      organic electron donor.
    supporting_text: "Reaction=H2O2 + AH2 = A + 2 H2O"
  - statement: >-
      UniProt records heme b as the cofactor, with one heme b bound per dimer.
    supporting_text: "Binds 1 heme b (iron(II)-protoporphyrin IX) group per dimer."
  - statement: >-
      UniProt notes the Trp-Tyr-Met crosslink is required for the catalase but not the
      peroxidase activity.
    supporting_text: "for the catalase, but not the peroxidase activity of the enzyme."
- id: file:interpro/panther/PTHR30555/PTHR30555-metadata.yaml
  title: >-
    PANTHER family PTHR30555 (HYDROPEROXIDASE I, BIFUNCTIONAL CATALASE-PEROXIDASE),
    subfamily PTHR30555:SF0 (CATALASE-PEROXIDASE)
  findings:
  - statement: >-
      katG (Q88GQ0) is classified in PANTHER family PTHR30555 and subfamily
      PTHR30555:SF0.
  - statement: >-
      The PANTHER family and subfamily names confirm the bifunctional
      catalase-peroxidase function of KatG.
- id: PMID:12534463
  title: >-
    Complete genome sequence and comparative analysis of the metabolically versatile
    Pseudomonas putida KT2440
  findings:
  - statement: >-
      The KT2440 genome sequencing and annotation effort that established the PP_3668
      (katG) locus and reference proteome entry.
    full_text_unavailable: true
- id: file:PSEPK/katG/katG-notes.md
  title: Curator notes for katG in Pseudomonas putida KT2440
  findings:
  - statement: >-
      Synthesis of UniProt evidence describing KatG as a central H2O2-scavenging enzyme
      in oxidative stress defense.
    supporting_text: >-
      central component of the cellular defense against oxidative/H2O2 stress.
core_functions:
- description: >-
    Heme b-dependent catalatic decomposition of hydrogen peroxide, dismutating two
    molecules of H2O2 into oxygen and water as a primary H2O2-detoxifying activity.
  molecular_function:
    id: GO:0004096
    label: catalase activity
  directly_involved_in:
  - id: GO:0042744
    label: hydrogen peroxide catabolic process
  - id: GO:0006979
    label: response to oxidative stress
  supported_by:
  - reference_id: file:PSEPK/katG/katG-uniprot.txt
    supporting_text: "Reaction=2 H2O2 = O2 + 2 H2O"
  - reference_id: file:PSEPK/katG/katG-uniprot.txt
    supporting_text: "Bifunctional enzyme with both catalase and broad-spectrum"
- description: >-
    Heme b-dependent broad-spectrum peroxidatic reduction of hydrogen peroxide using
    diverse organic electron donors, contributing to oxidative-stress defense.
  molecular_function:
    id: GO:0004601
    label: peroxidase activity
  directly_involved_in:
  - id: GO:0042744
    label: hydrogen peroxide catabolic process
  - id: GO:0006979
    label: response to oxidative stress
  supported_by:
  - reference_id: file:PSEPK/katG/katG-uniprot.txt
    supporting_text: "Reaction=H2O2 + AH2 = A + 2 H2O"
  - reference_id: file:PSEPK/katG/katG-uniprot.txt
    supporting_text: "Bifunctional enzyme with both catalase and broad-spectrum"
proposed_new_terms: []
suggested_questions:
- question: >-
    Is katG expression in Pseudomonas putida KT2440 induced by hydrogen peroxide or
    governed by an OxyR-type regulator, and how does it partition with other catalases
    in H2O2 defense?
  experts:
  - Bacterial oxidative-stress regulation specialists
  - Pseudomonas physiologists
- question: >-
    What is the relative in vivo contribution of the catalatic versus peroxidatic
    activity of KatG to H2O2 detoxification under different growth and stress
    conditions?
  experts:
  - Enzyme mechanism researchers
  - Redox biochemists
suggested_experiments:
- experiment_type: Gene knockout and phenotyping
  description: >-
    Delete katG (PP_3668) in KT2440, optionally in combination with other catalase
    genes, and measure H2O2 sensitivity, residual catalase/peroxidase activity, and
    survival under oxidative stress.
- experiment_type: Enzyme assay and cofactor analysis
  description: >-
    Purify recombinant KatG and confirm heme b incorporation, catalase and peroxidase
    activities, and the dependence of catalatic (but not peroxidatic) activity on the
    Trp-Tyr-Met crosslink via site-directed mutagenesis.
- experiment_type: Subcellular fractionation
  description: >-
    Fractionate KT2440 to verify the predicted cytosolic localization of KatG and rule
    out periplasmic or membrane association.