CG33116

UniProt ID: Q9VIU4
Organism: Drosophila melanogaster
Review Status: DRAFT
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Gene Description

CG33116 (dCCS1) is a seven-pass endoplasmic-reticulum membrane enzyme of the CDP-alcohol phosphotransferase family. It belongs to the invertebrate branch of the ethanolaminephosphotransferase (EPT1/SELENOI) lineage, the counterpart of the vertebrate selenoprotein SELENOI, and arose with its Golgi-associated paralog CG7149 from a fly-lineage duplication. By descent it is inferred to catalyze the final step of the CDP-ethanolamine (Kennedy) pathway, transferring phosphoethanolamine from CDP-ethanolamine to diacylglycerol to make phosphatidylethanolamine; it retains the complete CDP-alcohol phosphotransferase catalytic motif. Its enzymatic activity has not been measured directly. It is not the ceramide phosphoethanolamine synthase of Drosophila, which is the unrelated Golgi enzyme CG4585/Cpes.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0004307 ethanolaminephosphotransferase activity
IBA
GO_REF:0000033
ACCEPT
Summary: Core activity, inherited from the EPT1/SELENOI lineage in which CG33116 sits.
Reason: CG33116 is in PANTHER subfamily PTHR10414:SF71, the invertebrate EPT1-type subfamily (no vertebrate members; includes C. elegans ept-1), whose vertebrate counterpart SF47 is SELENOI/EPT1. This placement is supported by the identity pattern (about 48% to SELENOI versus 25-33% to CEPT1, CHPT1 and fly bbc) and by the primary paper, which states that CG33116 and CG7149 share a single human orthologue. The PAINT ancestor PTN000045767 carries this activity seeded by human SELENOI and CEPT1, both of which have experimental ethanolaminephosphotransferase activity. CG33116 keeps the complete CAPT catalytic motif. No direct assay of CG33116 exists, but nothing indicates a loss of function, and the IBA is accepted as the core activity. The same node now also carries a 2026 cholinephosphotransferase IBD, not present in the CG33116 GOA snapshot; because CG33116 is in the ethanolamine-specific SELENOI lineage, not the dual-specificity CEPT1 lineage, choline transfer is not assumed.
Propagation Review
Root cause: NO FAILURE CORE
Sources checked:
PANTHER:PTN000045767 SUPPORTS TRANSFER
The ancestor propagates ethanolaminephosphotransferase activity from experimentally characterized SELENOI/EPT1 and CEPT1 descendants. CG33116 (SF71) belongs to the invertebrate sister subfamily of SELENOI (SF47), so the transfer fits.
Supporting Evidence:
PMID:23449981
three proteins from the CEPT subfamily (dCCS1/CG33116, dCCS2/CG6016 and dCCS3/CG7149)
PMID:23449981
CG33116 and CG7149 (46% identity) have only one human orthologue and must therefore have originated from a gene duplication specific to the fly lineage
file:DROME/CG33116/CG33116-bioinformatics/RESULTS-rereview.md
PTHR10414:SF71 (CG33116's subfamily): 692 UniProt entries, 0 vertebrate,
file:DROME/CG33116/CG33116-bioinformatics/RESULTS-rereview.md
CG33116 retains every conserved motif residue, including the two terminal aspartates
GO:0005783 endoplasmic reticulum
IDA
PMID:23449981
Ceramide phosphoethanolamine biosynthesis in Drosophila is m...
ACCEPT
Summary: V5-tagged CG33116/dCCS1 localizes exclusively to the ER in Drosophila S2 cells and in HeLa cells.
Reason: In the full-text study, tagged dCCS1 shows reticular and nuclear-envelope staining that overlaps the ER marker PE-methyltransferase in S2 cells, and the HeLa assay gives the same result. A direct experimental localization that fits the multi-pass membrane architecture.
Supporting Evidence:
PMID:23449981
Both dCCS1-V5 and dCCS2-V5 localized exclusively to the ER, as evidenced by a reticular and nuclear envelope staining that overlapped extensively with the ER marker PE-methyltransferase
PMID:23449981
dCCS1 and dCCS2 localized exclusively to the ER, whereas dCCS3 and dCCS4 partially co-localized with the Golgi marker GM130
GO:0005789 endoplasmic reticulum membrane
IBA
GO_REF:0000033
ACCEPT
Summary: The inherited ER-membrane location is corroborated by direct ER localization of tagged CG33116.
Reason: The IBA is seeded by SELENOI and CEPT1, which are ER-membrane enzymes. For CG33116 it agrees with the direct S2-cell and HeLa localization and with its seven predicted transmembrane helices. This is the most specific location supported.
Propagation Review
Root cause: NO FAILURE CORE
Sources checked:
PANTHER:PTN000045767 SUPPORTS TRANSFER
This ancestor carries both ER and Golgi IBDs from diverged descendants. For CG33116 the ER-membrane assertion is confirmed by direct localization.
Supporting Evidence:
PMID:23449981
Both dCCS1-V5 and dCCS2-V5 localized exclusively to the ER, as evidenced by a reticular and nuclear envelope staining that overlapped extensively with the ER marker PE-methyltransferase
file:DROME/CG33116/CG33116-uniprot.txt
DR InterPro; IPR043130; CDP-OH_PTrfase_TM_dom.
GO:0005794 Golgi apparatus
IBA
GO_REF:0000033
REMOVE
Summary: Golgi residence was propagated from Golgi-localized relatives, but CG33116 itself was shown to localize only to the ER.
Reason: The Golgi IBD at PTN000045767 is seeded by CHPT1 (Q8WUD6, mouse Chpt1) and by FBgn0031948, which is CG7149/dCCS3, the fly paralog of CG33116. In the same experiment CG33116/dCCS1 localized exclusively to the ER in both S2 and HeLa cells, while CG7149/dCCS3 went partly to the Golgi. This is direct target-specific evidence that the compartment diverged after the fly-lineage duplication, and it contradicts Golgi residence for CG33116. The vertebrate EPT1-lineage member SELENOI, its closest characterized relative, is also an ER enzyme. The negative is supported by a direct experiment, not by low donor counts.
Propagation Review
Root cause: PROPAGATION BAD
Failure modes: COMPARTMENT OR COMPLEX MISMATCH
Sources checked:
PANTHER:PTN000045767 SUPPORTS SOURCE BUT NOT TARGET
Golgi localization holds for the seeds, including the fly paralog CG7149/dCCS3. The same study places CG33116/dCCS1 exclusively in the ER, so this deep ancestral node is the wrong level for a compartment that differs between the paralogs.
Supporting Evidence:
PMID:23449981
Both dCCS1-V5 and dCCS2-V5 localized exclusively to the ER, as evidenced by a reticular and nuclear envelope staining that overlapped extensively with the ER marker PE-methyltransferase
PMID:23449981
dCCS1 and dCCS2 localized exclusively to the ER, whereas dCCS3 and dCCS4 partially co-localized with the Golgi marker GM130
PMID:23449981
CG33116 and CG7149 (46% identity) have only one human orthologue and must therefore have originated from a gene duplication specific to the fly lineage
GO:0006646 phosphatidylethanolamine biosynthetic process
IBA
GO_REF:0000033
ACCEPT
Summary: Follows directly from the inherited ethanolaminephosphotransferase activity. That reaction is the final, PE-forming step of the CDP-ethanolamine pathway.
Reason: The CDP-ethanolamine:diacylglycerol ethanolaminephosphotransferase reaction itself produces phosphatidylethanolamine, so the gene product does the catalytic work of this process; this is participation, not mere requirement. The process is inherited with the activity from the SELENOI/CEPT1-seeded node and is consistent with CG33116's EPT1-lineage placement and ER residence. The CPE (sphingolipid) synthesis assayed in PMID:23449981 was attributed to CG4585, not CG33116, so no sphingolipid process is inferred here.
Propagation Review
Root cause: NO FAILURE CORE
Sources checked:
PANTHER:PTN000045767 SUPPORTS TRANSFER
PE biosynthesis is propagated from SELENOI/EPT1 and CEPT1 descendants and fits CG33116 as an invertebrate EPT1-lineage enzyme.
Supporting Evidence:
PMID:23449981
three proteins from the CEPT subfamily (dCCS1/CG33116, dCCS2/CG6016 and dCCS3/CG7149)
PMID:23449981
CG33116 and CG7149 (46% identity) have only one human orthologue and must therefore have originated from a gene duplication specific to the fly lineage
file:DROME/CG33116/CG33116-bioinformatics/RESULTS-rereview.md
PTHR10414:SF71 (CG33116's subfamily): 692 UniProt entries, 0 vertebrate,
GO:0008654 phospholipid biosynthetic process
IEA
GO_REF:0000002
MODIFY
Summary: Correct but general; refine to phosphatidylethanolamine biosynthetic process, which the gene already carries.
Reason: The InterPro CDP-alcohol phosphotransferase mapping is correct but does not specify the lipid. The phylogenetically supported role is PE synthesis (GO:0006646, a descendant of this term), which is already annotated by IBA.
Supporting Evidence:
PMID:23449981
three proteins from the CEPT subfamily (dCCS1/CG33116, dCCS2/CG6016 and dCCS3/CG7149)
file:DROME/CG33116/CG33116-bioinformatics/RESULTS-rereview.md
PTHR10414:SF71 (CG33116's subfamily): 692 UniProt entries, 0 vertebrate,
GO:0016020 membrane
IEA
GO_REF:0000120
MODIFY
Summary: Correct but general; refine to endoplasmic reticulum membrane.
Reason: CG33116 is a multi-pass membrane protein shown experimentally to reside in the ER. Endoplasmic reticulum membrane (GO:0005789), already carried by IBA, is the specific supported location.
Proposed replacements: endoplasmic reticulum membrane
Supporting Evidence:
PMID:23449981
Both dCCS1-V5 and dCCS2-V5 localized exclusively to the ER, as evidenced by a reticular and nuclear envelope staining that overlapped extensively with the ER marker PE-methyltransferase
file:DROME/CG33116/CG33116-uniprot.txt
DR InterPro; IPR043130; CDP-OH_PTrfase_TM_dom.
GO:0016780 phosphotransferase activity, for other substituted phosphate groups
IEA
GO_REF:0000002
MODIFY
Summary: Correct but general; refine to ethanolaminephosphotransferase activity, which the gene already carries.
Reason: The InterPro mapping is a donor-agnostic parent of the CDP-alcohol phosphotransferase activities. GO:0004307 ethanolaminephosphotransferase activity is an is_a descendant (via GO:0017169 CDP-alcohol phosphatidyltransferase activity) and is supported by CG33116's EPT1-lineage placement and intact catalytic motif. It is already annotated by IBA. Under the general-to-specific rule this is a MODIFY rather than a non-core keep.
Supporting Evidence:
file:DROME/CG33116/CG33116-bioinformatics/RESULTS-rereview.md
PTHR10414:SF71 (CG33116's subfamily): 692 UniProt entries, 0 vertebrate,
file:DROME/CG33116/CG33116-bioinformatics/RESULTS-rereview.md
CG33116 retains every conserved motif residue, including the two terminal aspartates

Core Functions

Transfers phosphoethanolamine from CDP-ethanolamine to diacylglycerol at the ER membrane, the final step of de novo phosphatidylethanolamine synthesis by the Kennedy pathway. This is inferred from its membership of the EPT1/SELENOI lineage; it has not been assayed directly.

Supporting Evidence:
  • PMID:23449981
    CG33116 and CG7149 (46% identity) have only one human orthologue and must therefore have originated from a gene duplication specific to the fly lineage
  • file:DROME/CG33116/CG33116-bioinformatics/RESULTS-rereview.md
    PTHR10414:SF71 (CG33116's subfamily): 692 UniProt entries, 0 vertebrate,
  • file:DROME/CG33116/CG33116-bioinformatics/RESULTS-rereview.md
    CG33116 retains every conserved motif residue, including the two terminal aspartates
  • PMID:23449981
    Both dCCS1-V5 and dCCS2-V5 localized exclusively to the ER, as evidenced by a reticular and nuclear envelope staining that overlapped extensively with the ER marker PE-methyltransferase

References

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Suggested Questions for Experts

Q: Does CG33116/dCCS1 use CDP-ethanolamine exclusively, as SELENOI does, or does it also transfer phosphocholine from CDP-choline? Does it accept 1-alkyl-2-acylglycerol, making ether-linked PE, as SELENOI does?

Suggested experts: Lipid biochemist with Drosophila Kennedy-pathway expertise

Q: After the fly-lineage duplication, how do the ER enzyme CG33116 and the Golgi-associated CG7149 divide PE synthesis between them, by tissue, by compartment or by acceptor?

Suggested Experiments

Experiment: Express CG33116 in yeast lacking ept1 and cpt1, or in SELENOI-null mammalian cells, and measure microsomal CDP-ethanolamine and CDP-choline phosphotransferase activity with diacyl and alkylacyl glycerol acceptors. Include a catalytic-aspartate (D134/D138) mutant as a control.

Experiment: Measure PE and plasmalogen-PE species by lipidomics in CG33116 and CG7149 single and double mutant flies or S2 RNAi cells, labelling with [14C]ethanolamine.

External Prediction Reviews

These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.

ProtNLM2 External predictions

View prediction review YAML Β· CG33116-protnlm-predictions-review.yaml Β· Review status: COMPLETE

All three broad predictions are supported but less precise than the ER-localized phosphatidylethanolamine-synthesis function.

Source documents: projects/PROTNLM_EVALUATION/fly-benchmark/predictions.jsonl.gz Β· genes/DROME/CG33116/CG33116-predictions-source.json

Review score: 2 = concordant with evidence; 1 = uncertain; 0 = discordant with evidence. This is an assessment score, not a model probability.

GO:0016780 phosphotransferase activity, for other substituted phosphate groups GO_MF
LSP β€” Less precise than existing annotation Review score: 2/2
Prediction method: ProtNLM2 Β· Version: UniProt API snapshot 2026-09-08
Review rationale: The phosphotransferase prediction agrees with CG33116 membership in the choline/ethanolamine phosphotransferase subfamily established in a primary comparative study. The PAINT assignment of ethanolaminephosphotransferase activity is more specific and is a reasonable conserved-reaction inference for this ER protein. The exact substrate activity has not been directly measured in the cited localization study. The predicted term is already in GOA as an InterPro-derived IEA, and the gene review refines it to GO:0004307, which the gene carries by IBA.
Supporting Evidence:
  • PMID:23449981: "three proteins from the CEPT subfamily (dCCS1/CG33116, dCCS2/CG6016 and dCCS3/CG7149)"
  • PMID:23449981: "Both dCCS1-V5 and dCCS2-V5 localized exclusively to the ER, as evidenced by a reticular and nuclear envelope staining that overlapped extensively with the ER marker PE-methyltransferase"
GO:0016020 membrane GO_CC
LSP β€” Less precise than existing annotation Review score: 2/2
Prediction method: ProtNLM2 Β· Version: UniProt API snapshot 2026-09-08
Review rationale: Membrane residence is supported by the membrane phosphotransferase architecture and direct localization of CG33116/dCCS1 to the ER. The existing ER-membrane annotation specifies the relevant compartment and is more informative than membrane. The predicted term is already in GOA by IEA, and the gene review refines it to GO:0005789.
Supporting Evidence:
  • PMID:23449981: "Both dCCS1-V5 and dCCS2-V5 localized exclusively to the ER, as evidenced by a reticular and nuclear envelope staining that overlapped extensively with the ER marker PE-methyltransferase"
  • file:DROME/CG33116/CG33116-uniprot.txt: "DR InterPro; IPR000462; CDP-OH_P_trans."
GO:0008654 phospholipid biosynthetic process GO_BP
LSP β€” Less precise than existing annotation Review score: 2/2
Prediction method: ProtNLM2 Β· Version: UniProt API snapshot 2026-09-08
Review rationale: The predicted phospholipid biosynthetic process is consistent with the conserved choline/ethanolamine phosphotransferase subfamily and ER localization. The curated phosphatidylethanolamine biosynthetic process is the supported, more specific pathway assignment. This inference concerns glycerophospholipid synthesis, distinct from the ceramide phosphoethanolamine synthesis experimentally assigned to CG4585. The predicted term is already in GOA by IEA, and the gene review refines it to GO:0006646, which the gene carries by IBA.
Supporting Evidence:
  • PMID:23449981: "three proteins from the CEPT subfamily (dCCS1/CG33116, dCCS2/CG6016 and dCCS3/CG7149)"
  • PMID:23449981: "Both dCCS1-V5 and dCCS2-V5 localized exclusively to the ER, as evidenced by a reticular and nuclear envelope staining that overlapped extensively with the ER marker PE-methyltransferase"

Deep Research

Falcon

(CG33116-deep-research-falcon.md)

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πŸ“š Additional Documentation

Notes

(CG33116-notes.md)

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