PP_0375

UniProt ID: Q88QV9
Organism: Pseudomonas putida (strain ATCC 47054 / DSM 6125 / CFBP 8728 / NCIMB 11950 / KT2440)
Review Status: DRAFT
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Gene Description

PP_0375 encodes an S9-family serine peptidase located immediately downstream of pqqE in the Pseudomonas putida KT2440 pyrroloquinoline quinone (PQQ) locus. The KT2440 operon study refers to PP_0375 as pqqG, and related Pseudomonas proteins are called PqqG, PqqM, or PqqH. Sequence and locus conservation support a PQQ-pathway association, but the native substrate and whether the protein acts in precursor maturation, PQQ excretion, or both have not been established.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0006508 proteolysis
IEA
GO_REF:0000002 		KEEP AS NON CORE
Summary: Proteolysis is a reasonable broad process annotation for PP_0375. The protein contains an S9 peptidase catalytic domain and is annotated as a prolyl oligopeptidase-family protein, although its native substrate is unknown.
Reason: The sequence-family evidence supports a proteolytic role, but the generic process is less informative than the serine-peptidase molecular function and the PQQ-pathway association. It does not specify that PqqA is the substrate.
Supporting Evidence:
file:PSEPK/PP_0375/PP_0375-goa.tsv
GO:0006508 proteolysis
file:PSEPK/PP_0375/PP_0375-uniprot.txt
DR InterPro; IPR001375; Peptidase_S9_cat.
GO:0008236 serine-type peptidase activity
IEA
GO_REF:0000002 		ACCEPT
Summary: Serine-type peptidase activity is supported by the S9 prolyl oligopeptidase catalytic domain and the conserved family assignment.
Reason: This is the most informative current molecular-function annotation for PP_0375, while substrate specificity remains unknown.
Supporting Evidence:
file:PSEPK/PP_0375/PP_0375-goa.tsv
GO:0008236 serine-type peptidase activity
file:PSEPK/PP_0375/PP_0375-uniprot.txt
DR InterPro; IPR001375; Peptidase_S9_cat.
file:PSEPK/PP_0375/PP_0375-uniprot.txt
DR PANTHER; PTHR43056:SF5; PEPTIDASE S9 PROLYL OLIGOPEPTIDASE CATALYTIC DOMAIN-CONTAINING PROTEIN; 1.

Core Functions

PP_0375 is a PQQ-locus-associated S9 serine peptidase in fluorescent pseudomonads. Its native substrate and whether it acts in precursor maturation, PQQ excretion, or both remain unknown.

Molecular Function:
serine-type peptidase activity
Supporting Evidence:
  • file:PSEPK/PP_0375/PP_0375-uniprot.txt
    DR InterPro; IPR001375; Peptidase_S9_cat.
  • PMID:27287323
    The pqq gene cluster (pqqFABCDEG) encodes at least two independent transcripts
  • PMID:19902179
    Gene PA1990 of Pseudomonas aeruginosa, located downstream of pqqE and encoding a putative peptidase, was shown to be involved in excretion of PQQ into the culture supernatant.
  • file:PSEPK/PP_0375/PP_0375-bioinformatics/RESULTS.md
    Q88QV9 aligned to AAX10035.1 at 66.0% amino-acid identity across 606 residues, covering 98.9% of Q88QV9 and 99.8% of AAX10035.1.
  • file:PSEPK/PP_0375/PP_0375-deep-research-openscientist.md
    The **exact peptide substrate of PP_0375 has not been experimentally established** and remains the principal knowledge gap.

References

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Suggested Questions for Experts

Q: Does PP_0375 directly cleave a PqqA-derived intermediate, promote PQQ excretion, or perform both functions, and how does its role differ from the M16-family PqqF route?

Suggested Experiments

Experiment: Quantify intracellular and extracellular PQQ and PqqA-derived peptide intermediates in wild-type, PP_0375 deletion, catalytic-serine mutant, and complemented strains, then test purified PP_0375 against unmodified and PqqE-cross-linked PqqA by LC-MS/MS.

Hypothesis: PP_0375 contributes serine-peptidase activity to PQQ precursor maturation in KT2440.

Type: targeted genetics and substrate-resolved peptidase assay

Deep Research

OpenScientist

(PP_0375-deep-research-openscientist.md)

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📚 Additional Documentation

Notes

(PP_0375-notes.md)

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Bioinformatics Results

(RESULTS.md)

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