CG4860 (Dmel\CG4860; FBgn0037999; UniProt Q9VGC2) is a Drosophila melanogaster mitochondrial flavoenzyme of the acyl-CoA dehydrogenase (ACAD) family. The 415-residue protein contains the three canonical ACAD domains (N-terminal, middle and C-terminal) and is assigned to the short-/branched-chain ACAD subfamily by CDD (SCAD_SBCAD), with a non-covalently bound FAD cofactor; it is predicted to act in mitochondrial fatty acid beta-oxidation, catalyzing the FAD-dependent alpha,beta-dehydrogenation of a saturated acyl-CoA thioester to the corresponding trans-2-enoyl-CoA with electron transfer to electron-transfer flavoprotein (ETF). It is one of two Drosophila genes (the other being its paralog Arc42/CG4703) predicted by orthology to correspond to human ACADS/SCAD. The precise acyl-chain-length substrate specificity of CG4860 is uncertain: the "short-chain specific"/butyryl-CoA (EC 1.3.8.1) designation carried by the protein derives entirely from automated rule-based (ARBA/InterPro/EC) inference rather than direct characterization, and the only in vivo functional test in the fly indicates that loss of the paralog Arc42, not CG4860, reproduces the short-chain (C4/butyrylcarnitine) profile of human SCAD deficiency, so CG4860's exact substrate range and physiological role within fly beta-oxidation remain to be established experimentally.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016937 short-chain fatty acyl-CoA dehydrogenase activity | IBA GO_REF:0000033 | MODIFY | Summary: Phylogenetically inferred (IBA) short-chain acyl-CoA dehydrogenase activity, propagated from the ACADS/SCAD PANTHER clade. CG4860 is a bona fide ACAD-family member, but its restriction to the short-chain (butyryl-CoA/C4) substrate class is not supported for this specific paralog: it is a family/clade inference, and the only in vivo fly test (Geronazzo et al. 2025) shows that loss of the paralog Arc42 - not CG4860 - reproduces the elevated-C4 (butyrylcarnitine) profile of human SCAD deficiency, while CG4860 knockout does not accumulate C4. Reason: The molecular function (an acyl-CoA dehydrogenase) is sound, but the short-chain chain-length specificity is an over-specific rule/clade inference that direct fly evidence does not support (and partly contradicts) for CG4860. Generalize to the parent acyl-CoA dehydrogenase activity term, which is well supported by domain architecture and the ISS/IEA evidence. An independent OpenScientist analysis (run blinded to this review action as a neutral function-assignment hypothesis) reached the same verdict - retain the general GO:0003995 and flag GO:0016937 as over-specific - and adds a structural determinant: a Leu-to-Thr substitution at the RIGIA+8 substrate-specificity position lining CG4860's binding pocket (CG4860 has a small polar Thr, whereas both human ACADS and the fly paralog Arc42 carry the bulky hydrophobic Leu), which could shift CG4860 away from strict short-chain specificity. Proposed replacements: acyl-CoA dehydrogenase activity Supporting Evidence: PMID:40519079 In contrast, we did not observe an elevation of acylcarnitine C4 in the homozygous CG4860 mutant flies as compared to controls in either condition file:DROME/CG4860/CG4860-hypotheses/function-hypothesis-go-0016937/openscientist.md The smaller, polar threonine could accommodate longer or differently branched substrates, potentially shifting CG4860's substrate preference away from strict short-chain specificity. PMID:40519079 the acylcarnitine profile for Arc42 loss of function mimics that of ACADS loss of function, while that of CG4860 does not |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetically inferred mitochondrial localization (is_active_in), propagated from the mitochondrial ACAD clade. Consistent with the ACAD family (mitochondrial matrix beta-oxidation enzymes) and with the UniProt "mitochondrial" naming; there is no fly-specific localization datum but the assignment is biologically appropriate for this enzyme class. Reason: Mitochondrial localization is the expected and consistent compartment for an acyl-CoA dehydrogenase family beta-oxidation enzyme; the IBA parent term is appropriate. Supporting Evidence: file:DROME/CG4860/CG4860-uniprot.txt Lipid metabolism; mitochondrial fatty acid beta-oxidation |
| GO:0033539 fatty acid beta-oxidation using acyl-CoA dehydrogenase | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetically inferred involvement in the acyl-CoA dehydrogenase-catalyzed step of fatty acid beta-oxidation. CG4860 is an ACAD-family enzyme and its knockout perturbs the fly acylcarnitine (beta-oxidation) pool, so participation in the ACAD step of beta-oxidation is a reasonable process annotation even though the specific substrate chain length is uncertain. Reason: The process (the ACAD step of fatty acid beta-oxidation) is concordant with CG4860 being an ACAD-family enzyme whose loss alters the acylcarnitine profile; this is more informative than generic fatty acid beta-oxidation and does not over-commit on substrate specificity. Supporting Evidence: PMID:40519079 Instead, we observed a significantly lower concentration of C4, and a significant elevation of C2 (acteylcarnitine) file:DROME/CG4860/CG4860-uniprot.txt Belongs to the acyl-CoA dehydrogenase family |
| GO:0046359 butyrate catabolic process | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: Phylogenetically inferred butyrate (butanoate, C4) catabolic process - a substrate-specific restatement of short-chain (butyryl-CoA/C4) ACAD activity. This is precisely the activity that the in vivo fly evidence attributes to the paralog Arc42 rather than to CG4860: CG4860 knockout does not accumulate C4 (butyrylcarnitine) and if anything shows lower C4. The C4-specific catabolic framing is therefore not supported for this paralog. Reason: The narrow C4/butyrate-specific process is an over-specific clade inference that the direct fly knockout does not support (and partly contradicts) for CG4860; short-chain/butyryl-CoA function maps to the paralog Arc42. Retained but flagged as over-annotated rather than removed, since it derives from a genuine phylogenetic propagation. Supporting Evidence: PMID:40519079 we did not observe an elevation of acylcarnitine C4 in the homozygous CG4860 mutant flies as compared to controls in either condition PMID:40519079 In human individuals with SCAD (short-chain acyl-CoA dehydrogenase) deficiency, the stereotypical acylcarnitine profile is dominated by elevated C4 (butyrylcarnitine) |
| GO:0003995 acyl-CoA dehydrogenase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic (ARBA/InterPro) annotation to the parent acyl-CoA dehydrogenase activity term. This family-level molecular function is well supported by the domain architecture (three ACAD domains; CDD SCAD_SBCAD) and the FAD cofactor, and it does not over-commit on chain-length specificity. This is the most defensible molecular-function annotation for CG4860. Reason: The general ACAD activity is strongly supported by conserved domains and FAD binding and is the appropriate, non-over-specific molecular function for this uncharacterized paralog. Supporting Evidence: file:DROME/CG4860/CG4860-uniprot.txt Belongs to the acyl-CoA dehydrogenase family |
| GO:0016627 oxidoreductase activity, acting on the CH-CH group of donors | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro-derived electronic annotation to an intermediate oxidoreductase term. The acyl-CoA dehydrogenase reaction oxidizes the alpha,beta (C2-C3) CH-CH bond of the acyl-CoA thioester, so this parent term is accurate for CG4860 as an ACAD-family enzyme. Reason: Correct intermediate-level term subsumed by the more specific acyl-CoA dehydrogenase activity; retained as non-core. Supporting Evidence: file:DROME/CG4860/CG4860-uniprot.txt Belongs to the acyl-CoA dehydrogenase family |
| GO:0016937 short-chain fatty acyl-CoA dehydrogenase activity | IEA GO_REF:0000003 | MODIFY | Summary: Electronic annotation derived from the EC 1.3.8.1 mapping (GO_REF:0000003). The EC number and the short-chain designation for CG4860 come from automated ARBA/EC rule inference on family membership, not from measured activity of this protein. As with the IBA short-chain term, the chain-length specificity is over-specific for CG4860, whose in vivo knockout does not reproduce short-chain (C4) SCAD deficiency (that phenotype maps to the paralog Arc42). Reason: The dehydrogenase molecular function is correct, but the EC/rule-derived short-chain specificity is not supported for this paralog. Generalize to the parent acyl-CoA dehydrogenase activity term. Proposed replacements: acyl-CoA dehydrogenase activity Supporting Evidence: PMID:40519079 the acylcarnitine profile for Arc42 loss of function mimics that of ACADS loss of function, while that of CG4860 does not |
| GO:0050660 flavin adenine dinucleotide binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro-derived FAD binding annotation. Acyl-CoA dehydrogenases are FAD-dependent flavoproteins, and UniProt records FAD as the cofactor for CG4860. FAD binding is intrinsic to the dehydrogenase mechanism and is well supported by the conserved ACAD flavoprotein architecture. Reason: FAD binding is a genuine, mechanistically essential molecular function for any ACAD-family enzyme and is consistent with the UniProt cofactor annotation and conserved domains. Supporting Evidence: file:DROME/CG4860/CG4860-uniprot.txt Belongs to the acyl-CoA dehydrogenase family |
| GO:0003995 acyl-CoA dehydrogenase activity | ISS PMID:22758915 An inventory of peroxisomal proteins and pathways in Drosoph... | ACCEPT | Summary: ISS annotation curated by FlyBase transferring the general acyl-CoA dehydrogenase activity from a reference protein (WITH UniProtKB:Q709F0), associated with the Drosophila peroxisomal proteome inventory (Faust et al. 2012). The transferred function is the family-level ACAD activity, not a short-chain-specific claim, and is consistent with the domain architecture and the general FAO role. The cached publication is abstract-only and does not itself discuss CG4860, but per curation guidance an experimental/ISS curator judgment to the general term should not be overruled from incomplete cached evidence. Reason: Homology-based transfer to the general (non-over-specific) ACAD activity term is defensible and concordant with CG4860 being an ACAD-family enzyme; the curator judgment stands. Supporting Evidence: file:DROME/CG4860/CG4860-uniprot.txt Belongs to the acyl-CoA dehydrogenase family |
| GO:0006635 fatty acid beta-oxidation | ISS PMID:22758915 An inventory of peroxisomal proteins and pathways in Drosoph... | ACCEPT | Summary: ISS annotation (FlyBase, WITH UniProtKB:Q709F0) placing CG4860 in fatty acid beta-oxidation. This general process is supported by CG4860's ACAD-family membership and by the fly knockout altering the acylcarnitine (beta-oxidation) pool. It does not commit to a specific acyl-chain length, so it remains appropriate despite the substrate-specificity uncertainty. Reason: Involvement in fatty acid beta-oxidation is concordant with the enzyme family and with the in vivo perturbation of acylcarnitines on CG4860 loss; the general BP term is safe and appropriate. Supporting Evidence: PMID:40519079 Instead, we observed a significantly lower concentration of C4, and a significant elevation of C2 (acteylcarnitine) file:DROME/CG4860/CG4860-uniprot.txt Lipid metabolism; mitochondrial fatty acid beta-oxidation |
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Download this section (compressed HTML)Q: What is the actual acyl-chain-length substrate specificity of CG4860, and does it differ from its paralog Arc42 (which appears to carry the canonical short-chain/butyryl-CoA SCAD activity in the fly)?
Q: Given that CG4860 knockout lowers C4 and uniquely elevates C2 (acetylcarnitine), does CG4860 have a role in ketone/acetyl-CoA utilization or in short-chain acyl-CoA synthesis rather than classical butyryl-CoA dehydrogenation, as tentatively suggested by Geronazzo et al. 2025?
Experiment: Enzyme kinetics on purified recombinant CG4860 across a panel of acyl-CoA substrates (C4-C12, plus branched-chain substrates such as isovaleryl-CoA, given the CDD SCAD_SBCAD / PANTHER IVD subfamily assignment) with ETF as electron acceptor, to define its true substrate preference and test whether it is genuinely short-chain-specific or has a different/broader specificity than Arc42.
Experiment: Metabolic and genetic dissection of the CG4860 knockout (and CG4860; Arc42 double mutant), including targeted acyl-CoA/acylcarnitine and ketone-body metabolomics under fed and starved conditions, to test the proposed roles in SCAD synthesis and/or ketone (acetyl-CoA) utilization and to distinguish CG4860's physiological function from that of Arc42.
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