CG4860 (Dmel\CG4860, FBgn0037999, UniProt Q9VGC2) — research notes

Research journal for the AI GO-annotation review of Drosophila melanogaster CG4860, a fatty
acid oxidation-family (acyl-CoA dehydrogenase) enzyme related to human ACADS/SCAD.

Identity and sequence facts (from local UniProt record)

Two Drosophila ACADS-like genes: CG4860 vs Arc42 (CG4703)

Drosophila has (at least) two DIOPT-predicted orthologs of human ACADS: Arc42 and CG4860.
The decisive fly-specific evidence comes from Geronazzo et al. 2025 (G3), who made CRISPR-Cas9
knockouts of putative FAO genes and read acylcarnitine profiles.

Interpretation for annotation

The only in vivo, fly-specific functional test of CG4860 (Geronazzo et al. 2025) argues
against CG4860 being the enzyme responsible for short-chain (butyryl-CoA / C4) acyl-CoA
dehydrogenation in the fly — that role belongs to its paralog Arc42. CG4860 KO does not
accumulate C4; if anything C4 falls. So the ARBA-derived "short-chain specific" and
"butyrate catabolic process" annotations are over-specific for this particular paralog:
they are family/rule inferences that the direct experiment does not support (and partly
contradicts) for CG4860.

However, CG4860 is unambiguously a member of the acyl-CoA dehydrogenase family (domains,
CDD SCAD_SBCAD, FAD cofactor) and participates in mitochondrial fatty acid beta-oxidation /
lipid catabolism; its knockout perturbs the acylcarnitine (β-oxidation) pool. So the
general family-level MF (acyl-CoA dehydrogenase activity, oxidoreductase acting on CH-CH,
FAD binding), the mitochondrial localization, and the general fatty-acid β-oxidation process
remain reasonable. What is NOT supported is the confident restriction to the short-chain /
butyryl-CoA (C4) substrate class for CG4860 specifically.

This is consistent with the review task guidance: treat chain-length specificity cautiously;
mark over-specific chain-length claims as over-annotated where unsupported.

Provenance of the existing GOA annotations (CG4860-goa.tsv)

Key conclusions for the review

  1. description: SCAD-like / acyl-CoA-dehydrogenase-family mitochondrial flavoenzyme,
    predicted to act in fatty acid β-oxidation; note substrate-specificity uncertainty — the
    "short-chain specific / butyryl-CoA" designation is rule-based (ARBA/TrEMBL) and is not
    supported (and is partly contradicted) by the one in vivo fly knockout study, in which the
    paralog Arc42, not CG4860, reproduces short-chain (C4) ACADS deficiency.
  2. Downgrade / flag the over-specific short-chain (GO:0016937) and butyrate catabolic
    (GO:0046359) annotations for CG4860; retain the general ACAD-family MF (GO:0003995),
    oxidoreductase (GO:0016627), FAD binding (GO:0050660), mitochondrion (GO:0005739), and
    general/ACAD-step fatty-acid β-oxidation (GO:0006635, GO:0033539) as reasonable.
  3. Do NOT overrule the FlyBase ISS experimental-transfer annotations to the general terms
    (GO:0003995, GO:0006635) — those are the safe, family-level claims and are consistent with
    the KO perturbing the β-oxidation/acylcarnitine pool.

References consulted