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. reference_proteome_assessments: - reference_proteomes: - UP000002195 status: NO_SUPPORTED_COUNTERPART reviewed_on: '2026-10-19' reason: Retain Q54FI4 as the primary Swiss-Prot accession. No significant reference-proteome hit was returned for the AX4 chlA sequence. Because the source and reference context are closely related, this is a notable gene-model or proteome-coverage question for UniProt. The negative protein search does not establish genomic absence; investigate its source genomic locus before drawing that conclusion. evidence: - type: PROTEOME_SEARCH description: MMseqs2 searched 12,726 sequences across UP000002195 at E <= 1e-5 and sensitivity 7.5, returning 0 hits. The search table and candidate FASTA are empty; no alignments were generated. The heuristic search does not establish genomic absence or unique locus identity. supported_by: - reference_id: file:DICDI/chlA/chlA-record-evidence.yaml supporting_text: 'target_sequence_count: 12726' - reference_id: file:DICDI/chlA/chlA-record-evidence.yaml supporting_text: 'candidate_count: 0' - type: PROTEOME_MEMBERSHIP description: The primary accession is outside every searched exact-taxon reference proteome. supported_by: - reference_id: file:DICDI/chlA/chlA-record-evidence.yaml supporting_text: 'primary_in_any_reference_proteome: false' - type: RECORD_HISTORY description: 'Sampled UniSave observations: 11-NOV-2015, entry version 56.: UP000002195; 02-DEC-2020, entry version 74.: UP000002195; 27-NOV-2024, entry version 90.: no Proteomes cross-reference. These dated observations do not establish uninterrupted membership/absence, the exact change date, or UniProt''s motivation.' supported_by: - reference_id: file:DICDI/chlA/chlA-record-evidence.yaml supporting_text: |- entry_date: 11-NOV-2015, entry version 56. proteomes: - UP000002195 - reference_id: file:DICDI/chlA/chlA-record-evidence.yaml supporting_text: |- entry_date: 02-DEC-2020, entry version 74. proteomes: - UP000002195 - reference_id: file:DICDI/chlA/chlA-record-evidence.yaml supporting_text: |- entry_date: 27-NOV-2024, entry version 90. proteomes: [] 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: file:DICDI/chlA/chlA-record-evidence.yaml title: Compact archived record and sequence evidence for Q54FI4 - 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