CG34171

UniProt ID: X2JEK1
Organism: Drosophila melanogaster
Review Status: COMPLETE
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Gene Description

CG34171 (SPH244) is a Drosophila melanogaster gene encoding a secreted serine protease homolog (SPH) of the S1A chymotrypsin-like family. It is listed among the S1A non-peptidase homologs, the protease-like proteins that have lost catalytic residues. The locus produces two polypeptides that share an N-terminal signal peptide and the first 167 residues. An alternative translation stop gives the 176-residue CG34171-PC product (X2JEK1). That product keeps the histidine and aspartate positions of the S1 catalytic triad but ends after the first half of the trypsin-like domain, so it lacks the C-terminal region that contains the catalytic serine. The 292-residue CG34171-PB product (A8DZ15) has a complete S1 domain with phenylalanine in place of the catalytic serine. Neither product is expected to be an active serine protease. Expression data show mild enrichment in testis, and transcripts are detected in Malpighian tubule. No biochemical, genetic or localization study of either product has been published. Its biological role, including whether it acts as a noncatalytic cofactor in an extracellular protease cascade as some insect SPHs do, is unknown.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0004252 serine-type endopeptidase activity
IKR NOT
PMID:30367934
Building a platform for predicting functions of serine prote... 		ACCEPT
Summary: The NOT annotation is correct. The X2JEK1 product lacks the C-terminal part of the S1 domain that carries the catalytic serine, and the longer product of the same gene has phenylalanine at that position.
Reason: This is a negated key-residue inference, and the evidence supports it. Cao and Jiang (2018) classified insect SP-related sequences as SPs or SPHs by whether they keep the His-Asp-Ser catalytic triad, and listed CG34171 as SPH244. FlyBase files the gene among the S1A non-peptidase homologs. The repository's alignment against active bovine trypsin (P00760) and the first, active S1 domain of toad ovochymase (Q66TN7) confirms the defect for this exact accession. X2JEK1 keeps H72 and D124, but its domain ends at residue 161, and no sequence aligns to the catalytic-serine region. A serine endopeptidase needs that serine as its nucleophile. PAINT reaches the same conclusion for this lineage: in PTHR24256, several Drosophila nodes carry NOT GO:0004252 IKR assertions that diverge from the catalytic ancestor PTN001207268. This is a sequence-based negative, not a failed enzyme assay. It is still the strongest claim the evidence supports.
Supporting Evidence:
file:DROME/CG34171/CG34171-bioinformatics/RESULTS.md
X2JEK1 preserves H72 and D124 but lacks the aligned catalytic-serine region. A8DZ15 has F222 at the serine-equivalent position.
PMID:30367934
based on the presence or absence of the His-Asp-Ser catalytic triad
file:DROME/CG34171/CG34171-flybase.txt
Serine protease homologs of the S1A family are similar in amino acid sequence to S1A serine proteases but are enzymatically inactive due to the lack of catalytic residue(s).
GO:0006508 proteolysis
IEA
GO_REF:0000002 		MARK AS OVER ANNOTATED
Summary: This term comes from mapping the trypsin-domain signature to GO, and it assumes catalytic peptide-bond hydrolysis. This product is not catalytic, and nothing shows it taking part in a proteolytic process by another route.
Reason: The IPR001254 to GO:0006508 mapping assumes that a trypsin-domain protein hydrolyses peptide bonds. That assumption fails here. The accepted NOT serine-type endopeptidase annotation and the sequence analysis show that X2JEK1 has lost the catalytic serine region, and FlyBase also records NOT peptidase activity for the gene by key-residue inference. Some insect SPHs do take part in proteolytic cascades as noncatalytic cofactors, so the term is not impossible. However, no data link CG34171 to any cascade, partner protease or substrate. PAINT made the same distinction. It propagated proteolysis (IBD) only from the catalytic node PTN001207268, and the gene's only phylogenetic process annotation is innate immune response, from PTN000667087. The gene carries no IBA proteolysis row. We treat that omission as a deliberate curator decision. The term is kept but marked as an over-annotation, not removed, because participation as a cofactor has not been ruled out.
Supporting Evidence:
file:DROME/CG34171/CG34171-bioinformatics/RESULTS.md
X2JEK1 preserves H72 and D124 but lacks the aligned catalytic-serine region. A8DZ15 has F222 at the serine-equivalent position.
file:DROME/CG34171/CG34171-flybase.txt
Serine protease homologs of the S1A family are similar in amino acid sequence to S1A serine proteases but are enzymatically inactive due to the lack of catalytic residue(s).
PMID:30367934
SPs and their non-catalytic homologs (SPHs) have

References

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Suggested Questions for Experts

Q: Is the 176-residue CG34171-PC product (X2JEK1) translated and stable in vivo, or is it a minor product of the multiphasic-reading-frame stop? It contains only the N-terminal half of a trypsin-like fold.

Q: Does CG34171 (either product) act as a noncatalytic cofactor or regulator in an extracellular serine protease cascade, as some insect SPHs do? If so, which catalytic protease does it partner with? This would justify, or refute, the gene-level IBA innate immune response and the IEA proteolysis rows.

Q: PANTHER placement differs by isoform and source. X2JEK1 is assigned to PTHR24256, and the gene's IBA comes from PTHR24256 node PTN000667087. UniProt maps A8DZ15 to PTHR24276:SF96, and the PANTHER 19.0 fly classification file maps it to PTHR24260:SF136. Which family placement do PAINT curators intend for this locus?

Suggested Experiments

Experiment: Isoform-specific proteomics or epitope-tagged knock-in alleles to find out whether the PC (X2JEK1) and PB (A8DZ15) products are both made, secreted, and where (testis, Malpighian tubule, hemolymph).

Experiment: Express and purify the CG34171-PB protein, test it for amidase or protease activity against chromogenic substrates (expected to be negative), and use co-immunoprecipitation from hemolymph after immune challenge to look for partner serine proteases.

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 · CG34171-protnlm-predictions-review.yaml · Review status: COMPLETE

The predicted serine-type endopeptidase activity is contradicted by the absence of the catalytic-serine region in the selected short CG34171 isoform.

Source documents: projects/PROTNLM_EVALUATION/fly-benchmark/predictions.jsonl.gz · genes/DROME/CG34171/CG34171-predictions-source.json · genes/DROME/CG34171/CG34171-bioinformatics/RESULTS.md

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

GO:0004252 serine-type endopeptidase activity GO_MF
NPI — Nonparalog incorrect Review score: 0/2
Prediction method: ProtNLM2 · Version: UniProt API snapshot 2026-09-08
DOMAIN ARCHITECTURE MISMATCH
Review rationale: X2JEK1 is the 176-residue CG34171-PC isoform, not the 292-residue PB product. Two alignment modes and two active S1-domain references place H72 and D124 at conserved catalytic positions, but the entire catalytic-serine region is absent from the short product. The longer product has F222 at that position; that is a separate substitution and must not be assigned to the missing short-product sequence. This contradicts the predicted intrinsic activity and agrees with the explicit NOT IKR annotation to the same term. The raw prediction records Q66TN7 as its donor at model score 0.99, but its hit coordinates and historical input sequence are unavailable. The decisive evidence is the reproduced catalytic-region defect, not agreement with a database label or the SPH synonym.
Supporting Evidence:

Deep Research

Falcon

(CG34171-deep-research-falcon.md)

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📚 Additional Documentation

Notes

(CG34171-notes.md)

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Bioinformatics Results

(RESULTS.md)

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📄 View Raw YAML

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