SCO2678

UniProt ID: Q9L243
Organism: Streptomyces coelicolor (strain ATCC BAA-471 / A3(2) / M145)
Review Status: DRAFT
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Gene Description

SCO2678 (Q9L243) is a 171-amino-acid Streptomyces coelicolor A3(2) HAD-superfamily protein with a HAD_SAK_2 domain (PF18143). Its conserved DxD, Thr/Ser, Lys, and DD motifs are consistent with Mg2+-dependent phosphomonoesterase activity, and its PF18143 family placement links it to RNA-repair-associated HAD hydrolases rather than characterized dNMP-acting 5-prime-nucleotidases. SCO2678 has no direct biochemical characterization or genetic study, and its physiological substrate, pathway, and cellular role remain unresolved.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0016791 phosphatase activity
ISM
file:STRCO/Q9L243/Q9L243-hypotheses/prediction-deoxyribonucleotide-catabolism/openscientist.md 		NEW
Summary: SCO2678 has a HAD_SAK_2 domain and the conserved HAD catalytic motifs needed for Mg2+-dependent phosphomonoester hydrolysis, but substrate specificity is not established.
Reason: The focused deoxyribonucleotide-catabolism audit found all four canonical HAD motifs in SCO2678 and supported a low-specificity phosphatase molecular function. It also found that the PF18143/HAD_SAK_2 assignment does not establish 5-prime-nucleotidase activity or dNMP catabolism. The older Falcon report's broad HAD-superfamily call is retained as corroborating context, but its secreted 5-prime-nucleotidase model has been superseded; this new generic phosphatase row therefore cites the focused audit as its originating evidence.
Supporting Evidence:
file:STRCO/Q9L243/Q9L243-hypotheses/prediction-deoxyribonucleotide-catabolism/openscientist.md
All four canonical HAD catalytic motifs are present and correctly spaced
GO:0005737 cytoplasm
ISM
file:STRCO/Q9L243/Q9L243-hypotheses/prediction-deoxyribonucleotide-catabolism/openscientist.md 		NEW
Summary: SCO2678 lacks a signal peptide or transmembrane segment and retains catalytic HAD Motif I at Asp13 near the N-terminus, arguing against a cleaved signal peptide and supporting a soluble cytoplasmic enzyme.
Reason: The focused localization analysis refutes the "Secreted protein" name as a generic TrEMBL label: the 171-residue enzyme has no hydrophobic signal peptide, no transmembrane segment, and an N-terminal catalytic aspartate incompatible with signal-peptide cleavage. This replaces the Falcon report's extracellular-region proposal because the focused sequence audit directly evaluated the full 171-aa target sequence and found no export signal.
Supporting Evidence:
file:STRCO/Q9L243/Q9L243-hypotheses/prediction-deoxyribonucleotide-catabolism/openscientist.md
SCO2678 is therefore a **soluble cytoplasmic HAD hydrolase**, not a secreted or membrane ecto-nucleotidase.

Core Functions

SCO2678 is a likely HAD-family phosphatase/phosphomonoesterase with intact Mg2+-dependent catalytic motifs. Its PF18143/HAD_SAK_2 assignment is associated with RNA-repair phosphoesterases and does not resolve the true physiological substrate. No direct assay establishes whether SCO2678 acts on free nucleotides, sugar phosphates, phosphorylated nucleic acid ends, or another phosphomonoester.

Molecular Function:
phosphatase activity
Cellular Locations:
cytoplasm
Supporting Evidence:
  • file:STRCO/Q9L243/Q9L243-hypotheses/prediction-deoxyribonucleotide-catabolism/openscientist.md
    The defensible molecular reality is narrow: SCO2678 is a **Mg²⁺-dependent HAD phosphomonoesterase of unknown physiological substrate**

References

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Suggested Questions for Experts

Q: What is the precise physiological substrate of SCO2678, and does it prefer phosphorylated RNA repair intermediates, free nucleotides, sugar phosphates, or another phosphomonoester class?

Q: Is SCO2678 expressed with RNA-repair genes or under stresses that generate damaged RNA termini, consistent with its PF18143/HAD_SAK_2 assignment?

Q: Does any biochemical or genetic evidence connect SCO2678 to deoxyribonucleotide catabolism, or was the ProtNLM2 pathway prediction an over-specific transfer from a generic HAD phosphatase label?

Suggested Experiments

Experiment: Heterologously express and purify SCO2678, then perform substrate profiling using a panel of 5'-nucleotides (AMP, GMP, CMP, UMP, dAMP, etc.), sugar phosphates (glucose-6-phosphate, fructose-6-phosphate), phosphorylated oligonucleotide ends, and generic phosphatase substrates (pNPP). Determine kinetic parameters (Km, kcat) for preferred substrates and test divalent metal ion dependence (Mg2+, Mn2+, Co2+) consistent with the HAD mechanism.

Hypothesis: SCO2678 is a HAD-family phosphatase whose preferred substrate is not yet known.

Type: biochemical assay

Experiment: Epitope-tag SCO2678 at its native locus and fractionate S. coelicolor cells and culture supernatants under phosphate-replete and phosphate-limited conditions. Immunoblot or targeted mass spectrometry should detect whether the protein remains cytoplasmic, as predicted by its missing signal peptide and N-terminal catalytic Asp13.

Hypothesis: SCO2678 is a soluble cytoplasmic HAD phosphatase rather than a secreted phosphatase.

Type: localization

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 · Q9L243-protnlm-predictions-review.yaml · Review status: COMPLETE

The HAD_SAK_2 domain assignment supports a phosphatase-family hypothesis, but nucleotide substrate specificity and deoxyribonucleotide catabolism are unresolved.

Source documents: genes/STRCO/Q9L243/Q9L243-uniprot.txt · genes/STRCO/Q9L243/Q9L243-goa.tsv · genes/STRCO/Q9L243/Q9L243-hypotheses/prediction-deoxyribonucleotide-catabolism/openscientist.md

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

GO:0008253 5'-nucleotidase activity GO_MF
UNC — Uncertain Review score: 1/2
Prediction method: ProtNLM2 · Version: UniProt 2024_06 pilot
Review rationale: The 171-residue target has a Pfam HAD_SAK_2 assignment and intact HAD-family phosphohydrolase motifs, but the focused report found no specific nucleotidase signature or characterized dNMP-acting subfamily relationship. The fold supports a low-specificity phosphatase hypothesis; it does not establish that the substrate is a nucleotide or that phosphate is removed at its 5-prime position. The inspected sources contain no target substrate assay or well-resolved experimentally characterized ortholog establishing that specificity. The predicted activity is absent from the cached annotations and remains uncertain.
Supporting Evidence:
GO:0009264 deoxyribonucleotide catabolic process GO_BP
NPI — Nonparalog incorrect Review score: 0/2
Prediction method: ProtNLM2 · Version: UniProt 2024_06 pilot
FREQUENCY BIAS
Review rationale: A HAD-family domain can motivate a phosphatase hypothesis but does not identify deoxyribonucleotides as physiological substrates. The focused report found that SCO2678 belongs to the PF18143 RNA-repair-associated HAD family rather than characterized dNMP-acting nucleotidase subfamilies, has no nucleotide-catabolism genomic context, and lacks target biochemical or pathway evidence. ProtNLM2 overextended a generic HAD phosphatase signal to a 5-prime-nucleotidase label and then to a pathway-level deoxyribonucleotide catabolic-process term. The predicted process is absent from the cached annotations and is too specific for the inspected evidence.
Supporting Evidence:

Deep Research

Falcon

(Q9L243-deep-research-falcon.md)

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OpenScientist

(Q9L243-hypotheses/prediction-deoxyribonucleotide-catabolism/openscientist.md)

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📄 View Raw YAML

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