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.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000117 | MODIFY | 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. Reason: The generic parent term should be replaced by the specific, experimentally supported molecular function of ChlA. Proposed replacements: flavin-dependent halogenase activity Supporting Evidence: PMID:20231486 both chlorination events in this pathway are carried out by the flavin-dependent halogenase ChlA |
| GO:0004497 monooxygenase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | 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. 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. Supporting Evidence: PMID:20231486 chlA from Dd encodes a flavin-dependent halogenase capable of catalyzing both chlorinations in the biosynthesis of DIF-1 |
| GO:0106266 3-chloro THPH synthase activity | EXP PMID:20231486 A flavin-dependent halogenase catalyzes the chlorination ste... | ACCEPT | 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. Reason: Direct in vitro reconstitution with purified ChlA demonstrates the first chlorination step, corresponding precisely to this term. Supporting Evidence: PMID:20231486 The chlorination of THPH and Cl-THPH can be reconstituted in vitro using purified ChlA protein |
| GO:0106267 3,5 dichloro-THPH synthase activity | EXP PMID:20231486 A flavin-dependent halogenase catalyzes the chlorination ste... | ACCEPT | 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. Reason: In vitro reconstitution shows ChlA performs both chlorinations, including the conversion of Cl-THPH to dichloro-THPH captured by this term. Supporting Evidence: PMID:20231486 both chlorination events in this pathway are carried out by the flavin-dependent halogenase ChlA |
| GO:0018893 dibenzofuran metabolic process | IMP PMID:36252029 Yellow polyketide pigment suppresses premature hatching in s... | UNDECIDED | 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. 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. |
| GO:0140907 flavin-dependent halogenase activity | IDA PMID:20231486 A flavin-dependent halogenase catalyzes the chlorination ste... | ACCEPT | 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. Reason: Experimental (IDA) evidence directly supports ChlA as a flavin-dependent halogenase; this is the accurate, informative molecular-function term. Supporting Evidence: PMID:20231486 both chlorination events in this pathway are carried out by the flavin-dependent halogenase ChlA PMID:20231486 Lysine-86 has been identified as an essential catalytic residue |
| GO:0030587 sorocarp development | HMP PMID:17659086 High-throughput analysis of spatio-temporal dynamics in Dict... | KEEP AS NON CORE | 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. 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. Supporting Evidence: PMID:20231486 disruption of chlA leads to the characteristic DIF-less phenotype of fragile slug formation and collapsed fruiting bodies |
| GO:0031148 DIF-1 biosynthetic process | IMP PMID:20231486 A flavin-dependent halogenase catalyzes the chlorination ste... | ACCEPT | 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. Reason: Directly supported by loss-of-function and biochemical evidence; ChlA is an essential biosynthetic enzyme of the DIF-1 pathway. Supporting Evidence: PMID:20231486 dichlorination by the flavin-dependent halogenase ChlA PMID:20231486 the synthesis of DIF-1 and related metabolites is also inhibited by this mutation |
| GO:0031153 slug development involved in sorocarp development | IMP PMID:20231486 A flavin-dependent halogenase catalyzes the chlorination ste... | KEEP AS NON CORE | 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. 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. Supporting Evidence: PMID:20231486 disruption of chlA leads to the characteristic DIF-less phenotype of fragile slug formation and collapsed fruiting bodies |
| GO:0031154 culmination involved in sorocarp development | IMP PMID:20231486 A flavin-dependent halogenase catalyzes the chlorination ste... | KEEP AS NON CORE | 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. Reason: The culmination defect is a downstream consequence of the DIF-less phenotype rather than a direct molecular function of ChlA. Supporting Evidence: PMID:20231486 disruption of chlA leads to the characteristic DIF-less phenotype of fragile slug formation and collapsed fruiting bodies |
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