chlA

id: Q54FI4
gene_symbol: chlA
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:44689
  label: Dictyostelium discoideum
description: ChlA (Chlorination protein A) is a soluble FAD-dependent halogenase
  from the social amoeba Dictyostelium discoideum that catalyzes the two sequential
  chlorination steps in the biosynthesis of DIF-1 (differentiation-inducing factor
  1), the polyketide-derived chlorinated morphogen that drives prestalk/stalk cell
  differentiation. Using reduced flavin (FADH2), molecular oxygen and chloride, ChlA
  converts the polyketide precursor THPH first to monochloro-THPH and then to
  dichloro-THPH; the dichlorinated product is subsequently O-methylated by DmtA to
  yield mature DIF-1. ChlA is encoded in a biosynthetic gene cluster with the
  polyketide synthase StlB, and its transcription rises during mid development in
  concert with stlB and dmtA. A conserved active-site lysine (Lys86) is essential
  for catalysis, consistent with the lysine-chloramine mechanism of flavin-dependent
  halogenases. Loss of ChlA abolishes DIF-1 production and produces the
  characteristic DIF-less developmental phenotype of fragile slugs and collapsed
  fruiting bodies.
existing_annotations:
- term:
    id: GO:0003824
    label: catalytic activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: enables
  review:
    summary: Root-level catalytic activity assigned by an ARBA machine-learning
      model. This is correct but entirely uninformative given that the specific
      enzymatic activity of ChlA (flavin-dependent halogenase) is experimentally
      established.
    action: MODIFY
    reason: The generic parent term should be replaced by the specific,
      experimentally supported molecular function of ChlA.
    proposed_replacement_terms:
    - id: GO:0140907
      label: flavin-dependent halogenase activity
    supported_by:
    - reference_id: PMID:20231486
      supporting_text: both chlorination events in this pathway are carried out by
        the flavin-dependent halogenase ChlA
- term:
    id: GO:0004497
    label: monooxygenase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: InterPro2GO inference from the flavin-dependent halogenase / FAD-binding
      domain. Flavin-dependent halogenases activate O2 to generate a flavin
      C4a-hydroperoxide and hypohalous acid, but the productive reaction transfers
      chloride to the substrate rather than incorporating an oxygen atom into it.
      Monooxygenase activity therefore mischaracterizes the catalytic outcome; the
      accurate molecular function is flavin-dependent halogenase activity, which is
      already directly annotated.
    action: MARK_AS_OVER_ANNOTATED
    reason: The monooxygenase keyword/domain mapping reflects the shared FAD-dependent
      oxidoreductase fold, not a hydroxylation activity. ChlA chlorinates its
      substrate; it does not incorporate oxygen into the product, so this IEA term
      over-annotates the true function captured by GO:0140907.
    supported_by:
    - reference_id: PMID:20231486
      supporting_text: chlA from Dd encodes a flavin-dependent halogenase capable of
        catalyzing both chlorinations in the biosynthesis of DIF-1
- term:
    id: GO:0106266
    label: 3-chloro THPH synthase activity
  evidence_type: EXP
  original_reference_id: PMID:20231486
  qualifier: enables
  review:
    summary: Experimentally supported. Purified ChlA catalyzes the first
      chlorination of the polyketide precursor THPH to monochloro-THPH in vitro,
      exactly matching this specific synthase-activity term. This is a core
      molecular function.
    action: ACCEPT
    reason: Direct in vitro reconstitution with purified ChlA demonstrates the first
      chlorination step, corresponding precisely to this term.
    supported_by:
    - reference_id: PMID:20231486
      supporting_text: The chlorination of THPH and Cl-THPH can be reconstituted in
        vitro using purified ChlA protein
- term:
    id: GO:0106267
    label: 3,5 dichloro-THPH synthase activity
  evidence_type: EXP
  original_reference_id: PMID:20231486
  qualifier: enables
  review:
    summary: Experimentally supported. ChlA catalyzes the second chlorination,
      converting monochloro-THPH to dichloro-THPH, the immediate DIF-1 precursor.
      This specific synthase term captures the second of the two chlorination events
      and is a core molecular function.
    action: ACCEPT
    reason: In vitro reconstitution shows ChlA performs both chlorinations, including
      the conversion of Cl-THPH to dichloro-THPH captured by this term.
    supported_by:
    - reference_id: PMID:20231486
      supporting_text: both chlorination events in this pathway are carried out by
        the flavin-dependent halogenase ChlA
- term:
    id: GO:0018893
    label: dibenzofuran metabolic process
  evidence_type: IMP
  original_reference_id: PMID:36252029
  qualifier: involved_in
  review:
    summary: This IMP annotation cites PMID:36252029, a study of the PKS5-derived
      yellow polyketide pigment and premature hatching in Dictyostelium. The cached
      full text does not mention ChlA, DIF-1, chlorination, or dibenzofuran, and
      dibenzofuran is a distinct chemical class from the chlorinated alkylphenone
      DIF-1 that ChlA produces. The supporting evidence for this term-gene pairing
      could not be verified.
    action: UNDECIDED
    reason: The full text of the cited reference does not appear to support a
      dibenzofuran metabolic role for ChlA, and the term is chemically inconsistent
      with the known DIF-1 substrate. Because the curator may have used data not
      reproduced in the cached text, this is flagged for expert re-examination
      rather than removed.
- term:
    id: GO:0140907
    label: flavin-dependent halogenase activity
  evidence_type: IDA
  original_reference_id: PMID:20231486
  qualifier: enables
  review:
    summary: Directly demonstrated. In vivo and in vitro evidence establishes ChlA
      as a flavin-dependent halogenase that catalyzes both chlorination steps of
      DIF-1 biosynthesis, with Lys86 identified as the essential catalytic residue.
      This is the central core molecular function of the protein.
    action: ACCEPT
    reason: Experimental (IDA) evidence directly supports ChlA as a flavin-dependent
      halogenase; this is the accurate, informative molecular-function term.
    supported_by:
    - reference_id: PMID:20231486
      supporting_text: both chlorination events in this pathway are carried out by
        the flavin-dependent halogenase ChlA
    - reference_id: PMID:20231486
      supporting_text: Lysine-86 has been identified as an essential catalytic
        residue
- term:
    id: GO:0030587
    label: sorocarp development
  evidence_type: HMP
  original_reference_id: PMID:17659086
  qualifier: acts_upstream_of_or_within
  review:
    summary: ChlA is required for normal fruiting body (sorocarp) formation because
      loss of ChlA abolishes DIF-1, causing fragile slugs and collapsed fruiting
      bodies. The gene acts upstream of sorocarp development by supplying the DIF-1
      morphogen rather than acting within the developmental program itself, so this
      broad developmental term is a valid but non-core annotation.
    action: KEEP_AS_NON_CORE
    reason: The developmental defect is a downstream consequence of loss of the
      ChlA-dependent DIF-1 signal. The annotation correctly places ChlA upstream of
      sorocarp development but does not describe its core molecular/biosynthetic
      function.
    supported_by:
    - reference_id: PMID:20231486
      supporting_text: disruption of chlA leads to the characteristic DIF-less
        phenotype of fragile slug formation and collapsed fruiting bodies
- term:
    id: GO:0031148
    label: DIF-1 biosynthetic process
  evidence_type: IMP
  original_reference_id: PMID:20231486
  qualifier: involved_in
  review:
    summary: ChlA carries out the dichlorination step of DIF-1 biosynthesis and its
      disruption blocks DIF-1 production. This directly and specifically describes
      the biological process in which ChlA participates and is a core annotation.
    action: ACCEPT
    reason: Directly supported by loss-of-function and biochemical evidence; ChlA is
      an essential biosynthetic enzyme of the DIF-1 pathway.
    supported_by:
    - reference_id: PMID:20231486
      supporting_text: dichlorination by the flavin-dependent halogenase ChlA
    - reference_id: PMID:20231486
      supporting_text: the synthesis of DIF-1 and related metabolites is also
        inhibited by this mutation
- term:
    id: GO:0031153
    label: slug development involved in sorocarp development
  evidence_type: IMP
  original_reference_id: PMID:20231486
  qualifier: acts_upstream_of_or_within
  review:
    summary: chlA mutants form fragile slugs, reflecting loss of the DIF-1 signal
      that patterns prestalk cells. ChlA acts upstream of slug development by
      providing the morphogen; this is a valid downstream developmental phenotype
      annotation but not the core function.
    action: KEEP_AS_NON_CORE
    reason: The fragile-slug phenotype is a consequence of absent DIF-1 signaling.
      The annotation correctly places ChlA upstream of slug development but is
      secondary to its enzymatic role.
    supported_by:
    - reference_id: PMID:20231486
      supporting_text: disruption of chlA leads to the characteristic DIF-less
        phenotype of fragile slug formation and collapsed fruiting bodies
- term:
    id: GO:0031154
    label: culmination involved in sorocarp development
  evidence_type: IMP
  original_reference_id: PMID:20231486
  qualifier: acts_upstream_of_or_within
  review:
    summary: chlA mutants show collapsed fruiting bodies, a culmination defect
      arising from loss of DIF-1-driven stalk cell formation. ChlA acts upstream of
      culmination by supplying the morphogen, making this a valid non-core
      developmental annotation.
    action: KEEP_AS_NON_CORE
    reason: The culmination defect is a downstream consequence of the DIF-less
      phenotype rather than a direct molecular function of ChlA.
    supported_by:
    - reference_id: PMID:20231486
      supporting_text: disruption of chlA leads to the characteristic DIF-less
        phenotype of fragile slug formation and collapsed fruiting bodies
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: PMID:17659086
  title: High-throughput analysis of spatio-temporal dynamics in Dictyostelium.
  findings: []
  reference_review:
    relevance: LOW
    correctness: UNVERIFIED
    review_notes: High-throughput mutant-phenotype (HMP) screen underlying the
      sorocarp-development annotation; chlA is not discussed by name in the cached
      text, so the specific phenotype call was not independently verified here.
- id: PMID:20231486
  title: A flavin-dependent halogenase catalyzes the chlorination step in the
    biosynthesis of Dictyostelium differentiation-inducing factor 1.
  findings:
  - statement: ChlA is a flavin-dependent halogenase that catalyzes both
      chlorination steps in DIF-1 biosynthesis, shown by in vivo and in vitro
      evidence.
    supporting_text: chlA from Dd encodes a flavin-dependent halogenase capable of
      catalyzing both chlorinations in the biosynthesis of DIF-1
  - statement: The chlorination of THPH and Cl-THPH is reconstituted in vitro with
      purified ChlA protein.
    supporting_text: The chlorination of THPH and Cl-THPH can be reconstituted in
      vitro using purified ChlA protein
  - statement: Lys86 is an essential catalytic residue, consistent with the
      lysine-chloramine halogenation mechanism.
    supporting_text: Lysine-86 has been identified as an essential catalytic residue
  - statement: chlA is clustered with the polyketide synthase stlB and its
      transcription rises with stlB and dmtA during mid development.
    supporting_text: Increased transcription of chlA coincides with rises in stlB
      and dmtA transcription
  - statement: The DIF-1 pathway comprises THPH formation by StlB, dichlorination by
      ChlA, and O-methylation by DmtA.
    supporting_text: dichlorination by the flavin-dependent halogenase ChlA
  - statement: Disrupting chlA gives a DIF-less phenotype of fragile slugs and
      collapsed fruiting bodies and blocks DIF-1 synthesis.
    supporting_text: disruption of chlA leads to the characteristic DIF-less
      phenotype of fragile slug formation and collapsed fruiting bodies
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Primary paper establishing ChlA as the DIF-1 halogenase; full text
      available and directly supports the molecular-function and DIF-1
      biosynthetic-process annotations.
- id: PMID:36252029
  title: Yellow polyketide pigment suppresses premature hatching in social amoeba.
  findings: []
  reference_review:
    relevance: LOW
    correctness: MISCITED
    review_notes: Cited for the dibenzofuran metabolic process (GO:0018893)
      annotation, but the cached full text concerns the PKS5-derived yellow pigment
      and premature hatching and does not mention ChlA, DIF-1, or dibenzofuran; the
      citation does not appear to support that annotation.
core_functions:
- description: ChlA is an FAD-dependent halogenase that catalyzes the two sequential
    chlorinations of the polyketide precursor THPH (to monochloro-THPH and then to
    dichloro-THPH), the committed tailoring steps that generate the immediate
    precursor of the stalk-inducing morphogen DIF-1.
  molecular_function:
    id: GO:0140907
    label: flavin-dependent halogenase activity
  directly_involved_in:
  - id: GO:0031148
    label: DIF-1 biosynthetic process
  supported_by:
  - reference_id: PMID:20231486
    supporting_text: both chlorination events in this pathway are carried out by the
      flavin-dependent halogenase ChlA
  - reference_id: PMID:20231486
    supporting_text: The chlorination of THPH and Cl-THPH can be reconstituted in
      vitro using purified ChlA protein