Egm (dACAD9 / Enigma / CG9006) — Drosophila melanogaster — Research Notes

UniProt: Q5U117 (ACAD9_DROME), 639 aa, Reviewed/Swiss-Prot. FlyBase: FBgn0086712.
Ortholog of human ACAD9 (Q9H845). PANTHER subfamily PTHR43884:SF9 "COMPLEX I ASSEMBLY
FACTOR ACAD9, MITOCHONDRIAL". Member of the acyl-CoA dehydrogenase (ACAD) family with a
predicted mitochondrial transit peptide (residues 1-26) and the ACAD9/ACADV-like C-terminal
domain (Pfam PF21343 ACAD9-ACADV_C). EC assigned as 1.3.8.- by similarity to human ACAD9.

Summary of function (synthesis)

Egm is the single Drosophila ortholog of human ACAD9. Like human ACAD9, its dominant,
essential role is as a mitochondrial respiratory chain complex I (CI) assembly factor and a
core component of the mitochondrial complex I intermediate assembly (MCIA) complex, together
with the fly orthologs of ECSIT (CG10610), NDUFAF1 (CG7598), TMEM126B (CG13392), and TMEM186
(CG4627). It retains an ACAD-family fold and (by similarity to human ACAD9) may retain
residual FAD-dependent acyl-CoA dehydrogenase activity toward long/very-long-chain acyl-CoA,
but the direct enzymatic activity of the fly protein has not been biochemically demonstrated.

Provenance from cached publications

PMID:16434470 (Mourikis et al. 2006, PNAS) — "Enigma" characterization. full_text_available: true

• Cloning/identity: Egm = CG9006 = 639-aa ACAD-homologous protein; two null alleles (Egm1, EgmP)
  are lethal and rescued by a WT genomic copy.
  PMID:16434470
• Subcellular localization: mitochondrial by immunocytochemistry (colocalizes with MitoTracker
  and prohibitin, an inner-membrane marker) and by cell fractionation.
  PMID:16434470
  PMID:16434470
• Essential gene / disruption phenotype: homozygous nulls die at late larval (third instar) stage;
  develop subcuticular melanotic masses, small eye/wing imaginal discs, malformed fat bodies;
  ~3.9-fold prolonged larval life; halved triglycerides.
  PMID:16434470
  PMID:16434470
• Lipid homeostasis / beta-oxidation link (INDIRECT/inferred): homology to ACADs + mitochondrial
  localization + reduced triglycerides + upregulated lipase-3 + eye clone phenotype resembling
  scully (a beta-oxidation component). Authors are explicit this is indirect.
  PMID:16434470
• Oxidative stress / longevity: heterozygous Egm mutants are more paraquat-resistant and longer-lived
  (female-specific).
  PMID:16434470
• Eye development (clonal, cell-autonomous):
  PMID:16434470
• NOTE: this 2006 paper predates the discovery that human ACAD9's primary role is CI assembly
  (Nouws 2010). Its FAO/lipid-homeostasis interpretation is best read, in light of later work
  (PMID:34386730 and human ACAD9), as downstream consequences of CI/OXPHOS deficiency in a fly that
  cannot assemble CI, rather than proof of a direct beta-oxidation enzyme role.

PMID:34386730 (Murari et al. 2021, iScience) — CI biogenesis; dACAD9 assayed. full_text_available: true

• dACAD9 (= CG9006 = Egm) is treated as the fly ACAD9 ortholog and a component of the MCIA complex.
  PMID:34386730
  PMID:34386730
• MCIA components (including dACAD9) remain associated with the assembled CI holoenzyme and with
  stalled assembly intermediates.
  PMID:34386730
• FUNCTION (fly): dACAD9 regulates biogenesis of the PP-b (ND2) sub-module; dACAD9 knockdown
  destabilizes the other MCIA members (dNDUFAF1, dECSIT) in assembly intermediates.
  PMID:34386730
  PMID:34386730
  PMID:34386730
• This directly parallels human ACAD9 in the MCIA complex (Nouws 2010; Formosa 2020) and is the
  basis for the IDA (GO:0160295, MCIA complex) and TAS (GO:0032981, CI assembly) annotations, and
  the ISS transfer of the adaptor-activity term from human ACAD9.

PMID:18666829 (Findlay et al. 2008, PLoS Biol) — seminal fluid proteomics. full_text_available: true

• Egm was detected among transferred seminal fluid proteins (HEP, GO:0007320 insemination). This is
  a mass-spec detection of the protein in seminal fluid, categorized under "lipid metabolism"
  proteins; it is a proteomic co-occurrence, NOT a demonstrated reproductive function of Egm.
  PMID:18666829
  (Egm is one of the lipid-metabolism-category Sfps in the paper's protein tables.)

PMID:23667151 (Chow et al. 2013, PNAS) — ER stress natural variation (DGRP). full_text_available: true

• Egm was one of six lipid-metabolism-related association candidates for TM-induced ER-stress survival
  (HMP, GO:0034976). This is a GWAS/association + P-element functional-test candidate; a putative,
  correlative role rather than a mechanistic one.
  PMID:23667151

PMID:26362788 (Chen et al. 2015, PNAS) — APEX mitochondrial-matrix proteomics. full_text_available: true

• APEX-based proteomic mapping of the Drosophila muscle mitochondrial matrix ("MitoMax"). Egm was
  catalogued in the matrix proteome (source of the IDA GO:0005759 mitochondrial matrix annotation).
  PMID:26362788
  (Egm/CG9006 appears in the MitoMax matrix inventory; matrix placement is consistent with a
  peripheral inner-membrane, matrix-facing MCIA factor.)

PMID:8913755 (Verheyen et al. 1996, Genetics) — Notch modifier screen. full_text_available: FALSE (abstract only)

• Large-scale second-site screen for dominant enhancers/suppressors of activated-Notch rough-eye
  phenotype (137,000 flies, 290 modifiers). Basis for the IGI GO:0001745 compound eye morphogenesis
  annotation (Egm as a Notch-eye modifier). Abstract-only in cache; the specific Egm/CG9006 allele
  data are in the full text not available here.
  PMID:8913755

Interpretation for review decisions

• CORE: CI assembly factor / MCIA complex member. Strong: GO:0160295 (IDA), GO:0032981 (TAS),
  GO:0030674 adaptor activity (ISS from human ACAD9), mitochondrion (IDA x2), mitochondrial matrix (IDA).
• SECONDARY / by-similarity enzymatic: FAD binding (IEA InterPro), oxidoreductase CH-CH (IEA InterPro),
  VLCAD activity (ISS from human ACAD9), medium-chain ACAD activity (IBA), fatty acid metabolic/beta-ox
  (IEA/IBA/IMP). The fly's own dehydrogenase activity is not directly demonstrated; human ACAD9's
  is modest (~18% VLCAD) and its FAO role is secondary/moonlighting. Keep these NON-CORE.
• The IMP FAO/lipid-homeostasis annotations (PMID:16434470) rest on indirect evidence and predate the
  CI-assembly-factor paradigm. The mutant phenotypes (triglyceride loss, lethality) are equally
  explained by CI/OXPHOS failure. Keep as non-core (do not REMOVE experimental annotations).
• Insemination (HEP), ER stress (HMP), compound eye (IGI), oxidative-stress (IMP): pleiotropic /
  systemic-consequence or proteomic-cooccurrence annotations. Keep as non-core; eye/ER/insemination
  are likely secondary to the gene's essential mitochondrial role. IGI eye annotation (PMID:8913755)
  is abstract-only in cache — but it is an experimental (IGI) FlyBase call; keep as non-core.

2026-09-20 full-gene re-review

All 22 source rows reviewed. Cytoplasm includes mitochondria (live GO:0005737 definition and part_of edge), so the IBA is ACCEPT. MCIA assembly remains the central core function, supported directly by PMID:34386730 Fig. 6 and the Egm/CG9006 identity. PMID:16434470 directly establishes mitochondrial localization, lipid/eye and oxidative-stress phenotypes but explicitly calls beta-oxidation evidence indirect; later complex-I evidence does not prove absence of additional catalysis.

Human ACAD9 is the actual same-subfamily ISS donor. PMID:16020546 full author manuscript Results and Fig. 4 assay purified enzyme with C6, C8, C9, C10, C11, C12 and longer substrates using ETF reduction at 50 micromolar. The full primary describes “activity toward a broad range of substrates”. Activity drops below C10; a long-chain optimum is not exclusivity, and GO medium-chain includes C6–C12. Human ACAD9 has live IDA GO:0070991 from this paper. Medium-chain MF is retained as inferred noncore; very-long-chain C22:6 activity is also real and not invalidated by the optimum. The fly enzyme remains unmeasured.

PMID:25721401 (verified title and PMC4424958, not the initially unverified PMID:25539954) full Results report unchanged octanoate oxidation in ACAD9 knockout HEK293 cells alongside reduced palmitate oxidation and rescue. This separates physiological substrate flux from in-vitro capacity without proving no conditional medium-chain contribution. Medium-chain catabolic BP is UNDECIDED pending the focused OpenScientist question. Exact-target global cache and local report checks were negative before submission.

Current PAINT places GO:0051793/GO:0070991 at PTN000098033. The independently retrieved PTHR43884 treeinfo v19 response contains human ACAD9 Q9H845 but neither Q5U117 nor that source node. No target ancestry or specific loss is invented; compact source hashes and node paths are recorded in the project organelle-paint-lineages.json.

Full PMID:18666829 isotopic transfer proteomics supports Egm as transferred seminal material, not an assumed contaminant. GO:0007320 describes introduction of semen/sperm; transfer as cargo does not demonstrate the protein performs that step, so the process over-annotation call remains. Full PMID:23667151 identifies Egm among lipid-related tunicamycin-survival candidates; retain noncore modifier evidence. PMID:26362788 supports APEX mitochondrial-matrix localization. PMID:8913755 remains abstract-only; independent Egm-null eye clones in PMID:16434470 support the retained noncore eye-development annotation.

Recovery review consistency follow-up (2026-09-22)

Restored readable identifiers in manual prose. Where applicable, reconciled AP3M2 reference notes with the retained contextual claim, removed unrelated PIK3C3 support from unresolved projections, separated PIK3C3 aspect-specific reasons, and documented the surviving/renamed ATG14 membrane term. Source assertion fields and verbatim quotations are unchanged.