CG43124 (SPH249) is a predicted secreted serine-protease homolog of Drosophila melanogaster. Its single annotated 245-residue polypeptide contains a trypsin-like region but substitutes serine and asparagine for two essential catalytic-triad residues, supporting a noncatalytic pseudoenzyme identity. A phylogenetically inferred role in innate immunity is compatible with the nonenzymatic functions of insect serine-protease homologs. Its specific molecular partners and effector mechanism remain uncharacterized.
Summary: The native noncatalytic molecular function is unresolved.
Reason: The ND root term records unknown molecular function rather than an enzyme activity. Catalytic-triad substitutions support absence of conventional peptidase activity, but do not identify a positive binding, cofactor or regulatory function. Retain the uncertainty marker without presenting it as a mechanistic core function.
IKRNOT PMID:30367934 Building a platform for predicting functions of serine prote...
ACCEPT
Summary: Accept the negated peptidase annotation: CG43124 is a noncatalytic serine-protease homolog.
Reason: The annotation is explicitly NOT, and its absence-of-key-residues inference is supported by an independent profile alignment of the exact 245-residue CG43124-PA sequence. The conserved catalytic histidine and aspartate positions align to Ser69 and Asn112 in a significant trypsin-domain segment, while the active trypsin control recovers all three catalytic residues. Cao and Jiang classify SP versus SPH proteins using this triad criterion. The C-terminal catalytic-serine position cannot be mapped reliably, so no third-site replacement is claimed. This is a sequence-based loss-of-catalysis assessment, not a direct biochemical inactivity assay.
Summary: The ND location placeholder is superseded by supported extracellular localization.
Reason: A more informative extracellular-region annotation is supported by the PAINT ancestral inference and the target N-terminal secretion signal. The cellular-component root does not add a distinct localization claim.
Summary: Extracellular localization is a reasonable conserved-family inference.
Reason: The PAINT IBA is a curated ancestral localization inference, and the exact target sequence independently has a predicted N-terminal signal peptide at residues 1–20. There is no contrary localization evidence or sequence feature suggesting loss of classical secretion. Together these support extracellular localization by inference; neither extracellular-matrix residence nor direct localization experiments are asserted.
Summary: A trypsin-domain mapping alone does not establish proteolysis by this inactive homolog.
Reason: The InterPro-derived IEA transfers a process term from the trypsin fold, but the exact protein lacks essential catalytic residues. Intrinsic proteolysis is therefore unsupported. A noncatalytic serine-protease homolog could still participate in a proteolytic cascade as a cofactor, so catalytic loss does not refute the biological-process term in principle. No CG43124-specific cascade mechanism or partner establishes that participation; the generic domain-to-process mapping exceeds its evidence.
SPHs are enzymatically inactive due to the lack of catalytic residue(s) but some of them (e.g. Masquerade) have known regulatory functions, including somatic muscle attachment, axonal guidance, post-mating responses, and prophenoloxidase (proPO) activation by proPO activating proteases (PAPs)
Summary: The biological-process ND placeholder is superseded by the retained immune-process inference.
Reason: The reviewed IBA already provides a meaningful innate-immunity process assignment. The biological-process root contributes no separate biological claim and should not be retained as a second process annotation.
Summary: Accept the negated peptidase annotation: CG43124 is a noncatalytic serine-protease homolog.
Reason: The annotation is explicitly NOT, and its absence-of-key-residues inference is supported by an independent profile alignment of the exact 245-residue CG43124-PA sequence. The conserved catalytic histidine and aspartate positions align to Ser69 and Asn112 in a significant trypsin-domain segment, while the active trypsin control recovers all three catalytic residues. Cao and Jiang classify SP versus SPH proteins using this triad criterion. The C-terminal catalytic-serine position cannot be mapped reliably, so no third-site replacement is claimed. This is a sequence-based loss-of-catalysis assessment, not a direct biochemical inactivity assay.
Summary: Retain the curated phylogenetic inference of an innate-immune role.
Reason: PAINT places this immune-process assertion at ancestral node PTN000667087. The catalytic-triad replacements challenge enzymatic activity, not descent from an immune-associated family: inactive insect serine-protease homologs can retain defense functions. No target-specific loss of the inferred immune role is established. Retain the IBA at its broad process level while leaving the CG43124-specific immune effector mechanism unresolved; no specific proteolytic cascade or direct target experiment is inferred from the annotation.
SPHs are enzymatically inactive due to the lack of catalytic residue(s) but some of them (e.g. Masquerade) have known regulatory functions, including somatic muscle attachment, axonal guidance, post-mating responses, and prophenoloxidase (proPO) activation by proPO activating proteases (PAPs)
SPHs are enzymatically inactive due to the lack of catalytic residue(s) but some of them (e.g. Masquerade) have known regulatory functions, including somatic muscle attachment, axonal guidance, post-mating responses, and prophenoloxidase (proPO) activation by proPO activating proteases (PAPs)
Q: Which extracellular partners and molecular activity mediate the inferred innate-immune role of CG43124?
Q: Does CG43124 serve as a noncatalytic cofactor in a defined protease cascade?
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.
The predicted serine-type endopeptidase activity is contradicted by loss of essential catalytic-triad residues in the exact CG43124 polypeptide. The trypsin-like sequence supports a noncatalytic homolog, not an active serine protease.
Review rationale: The exact target is the single 245-residue CG43124-PA polypeptide. Reproducible PF00089 profile alignment maps the essential trypsin catalytic histidine and aspartate to target Ser69 and Asn112 within a significant homologous segment; active bovine trypsin provides a successful positive control. The catalytic-serine region is poorly aligned, so a third substitution is not asserted. These two replacements contradict conventional serine endopeptidase chemistry and support a noncatalytic homolog. The original prediction has model score 0.98 and phmmer donor Q90WD8, toad ovochymase-2; fold similarity to this protease does not restore the missing target catalytic residues. Target GOA contains an explicit NOT annotation for the same activity, consistent with this independent analysis. Opposite polarity is not an equivalent existing positive annotation or CNN. Pseudoenzyme overannotation is supported; prediction-time sequence identity and the native noncatalytic function remain unestablished.
PMID:30367934: "The SP-related sequences in each species were divided into SPs or SPHs based on the presence or absence of the His-Asp-Ser catalytic triad"