SCO2678

UniProt ID: Q9L243
Organism: Streptomyces coelicolor A3(2)
Review Status: DRAFT
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Gene Description

SCO2678 (Q9L243) is a 171-amino-acid protein of Streptomyces coelicolor A3(2) consisting almost entirely of a haloacid dehalogenase (HAD)-superfamily domain of the HAD_SAK_2 family (Pfam PF18143), a family first described in large eukaryotic multidomain proteins predicted to act in RNA repair. It retains all four HAD core catalytic motifs (Asp13/Asp15, Thr67, Lys106, Asp123/Asp124), so it is predicted to be a Mg2+-dependent phosphatase that hydrolyses a phosphomonoester through an aspartyl-phosphate intermediate. It has no signal peptide, Tat signal or lipobox and is predicted to be a soluble cytoplasmic protein. Its substrate, pathway and physiological role are unknown; no member of the HAD_SAK_2 family has been characterized experimentally and SCO2678 is not encoded next to RNA-repair genes.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0016791 phosphatase activity
ISM
file:STRCO/Q9L243/Q9L243-bioinformatics/RESULTS-rereview.md 		NEW
Summary: Proposed from sequence: the HAD_SAK_2 domain spans residues 9-155 and all four HAD catalytic motifs are conserved, supporting a generic Mg2+-dependent phosphomonoesterase activity of unknown substrate.
Reason: GOA has no annotations for this protein. Re-reviewed independently: the PF18143 family is described as HAD-domain phosphoesterases removing phosphate groups, and the target keeps the motif I nucleophile/acid pair, motif II Thr, motif III Lys and motif IV Asp-Asp metal ligands. The generic term is as specific as the evidence allows. No characterized PF18143 member, PANTHER family or PAINT node exists, so no substrate-specific activity (5'-nucleotidase, RNA 3'-phosphatase or 2',3'-cyclic phosphatase, trehalose-6-phosphate phosphatase from the eggNOG COG1877 grouping) is transferred.
Supporting Evidence:
file:STRCO/Q9L243/Q9L243-bioinformatics/RESULTS-rereview.md
All four core HAD motifs are present in the expected N-to-C order with typical spacing
file:STRCO/Q9L243/Q9L243-bioinformatics/RESULTS-rereview.md
Family of HAD domain phophoesterases observed in large eukaryotic proteins with predicted role in RNA repair
GO:0005737 cytoplasm
ISM
file:STRCO/Q9L243/Q9L243-bioinformatics/RESULTS-rereview.md 		NEW
Summary: No signal peptide, twin-arginine signal, lipobox or transmembrane segment; the catalytic motif I lies within the N-terminal region a signal peptide would occupy.
Reason: A sequence-based localization inference for a small soluble enzyme. It contradicts the machine-generated UniProt name "Secreted protein" (ProtNLM, ECO:0008006), which is not evidence. The inference rests on absence of export signals and is not experimentally verified.
Supporting Evidence:
file:STRCO/Q9L243/Q9L243-bioinformatics/RESULTS-rereview.md
Conclusion: no evidence for export; the "Secreted protein" name in UniProt is a machine-generated label (ECO:0008006) and is not supported by the sequence.

Core Functions

Predicted Mg2+-dependent HAD-superfamily phosphomonoesterase of unknown substrate, inferred from an intact HAD catalytic core in a HAD_SAK_2 (PF18143) domain. No characterized family member constrains the substrate.

Molecular Function:
phosphatase activity
Cellular Locations:
cytoplasm
Supporting Evidence:
  • file:STRCO/Q9L243/Q9L243-bioinformatics/RESULTS-rereview.md
    so the protein is predicted to retain the aspartyl-phosphate HAD phosphoryl-transfer mechanism

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: Do bacterial stand-alone HAD_SAK_2 proteins such as SCO2678 form a monophyletic group distinct from the eukaryotic multidomain RNA-repair proteins in which the family was defined, and are any of them encoded next to RNA ligases or polynucleotide kinases in other genomes?

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

ProtNLM2 emitted two GO predictions for SCO2678, a 171-residue stand-alone HAD_SAK_2 (Pfam PF18143) protein with no GOA annotations. The intact HAD catalytic motifs support only a generic phosphatase activity of unknown substrate; no characterized PF18143 member, PANTHER family or PAINT node exists, and no publication on SCO2678 was found in PubMed. Both the 5'-nucleotidase activity and the deoxyribonucleotide catabolic process predictions are therefore unsupported but not refuted (UNC).

Source documents: genes/STRCO/Q9L243/Q9L243-uniprot.txt · genes/STRCO/Q9L243/Q9L243-goa.tsv · genes/STRCO/Q9L243/Q9L243-bioinformatics/RESULTS-rereview.md · 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: GOA has no annotations for SCO2678, so the term is novel. The sole family signature is Pfam PF18143 (HAD_SAK_2), and a reproducible motif scan finds all four HAD catalytic motifs, which supports a generic Mg2+-dependent phosphatase activity (the gene review's only core function). PF18143 was defined from eukaryotic RNA-repair-associated proteins, no member has been characterized, and the family is not one of the HAD subfamilies containing experimentally characterized 5'-nucleotidases, so there is no justified phylogenetic transfer of nucleotide substrate specificity. No PubMed record describes SCO2678 or a characterized ortholog. The prediction is a plausible refinement of the supported phosphatase activity, but no evidence establishes or excludes nucleotides as substrates, so it remains uncertain.
Supporting Evidence:
GO:0009264 deoxyribonucleotide catabolic process GO_BP
UNC — Uncertain Review score: 1/2
Prediction method: ProtNLM2 · Version: UniProt 2024_06 pilot
Review rationale: GOA has no annotations for SCO2678, so the term is novel. Participation in deoxyribonucleotide catabolism would require dNMP hydrolysis, which is itself unsupported: the protein is a stand-alone HAD_SAK_2 (PF18143) domain with no characterized family member and shares no Pfam family with HAD enzymes shown to dephosphorylate dNMPs. Its KEGG neighbourhood contains no nucleotide-catabolism genes (and no RNA-repair genes either), and PubMed has no study of SCO2678. The OpenScientist analysis reaches the same evidential picture. Absence of supporting evidence does not refute the process, because the substrate of this HAD phosphatase is unknown, so the prediction is uncertain rather than incorrect.
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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📚 Additional Documentation

Notes

(Q9L243-notes.md)

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📄 View Raw YAML

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