pqsB (Q9I4X2, PA0997) — review notes

Part of the BGC exemplar curation project (projects/BGC.md). MIBiG BGC0000922
(P. aeruginosa PAO1, 2-alkyl-4-quinolone / PQS-precursor cluster). GenBank
AAG04386.1 → UniProt Q9I4X2 (PQSB_PSEAE), gene pqsB / PA0997.

Function

PqsB is the non-catalytic subunit of the heterodimeric condensing enzyme PqsBC
that makes 2-heptyl-4(1H)-quinolone (HHQ) in the pqs quorum-sensing pathway
(see pqsC-notes.md for the full pathway).

• PqsB lacks the catalytic residues (the active-site Cys-129/His-269 reside in
  PqsC) but is tightly associated with PqsC and required for the condensation
  step; the octanoyl group is carried on PqsC.
  PMID:24239007
• Crystal structure (PDB 5DWZ): the PqsBC complex is "unique for its heterodimeric
  arrangement" PMID:26811339. PqsB contributes to the structure/stability and
  activity of the assembled heterodimer — a textbook "only functional when
  assembled" complex.
• A pqsB mutant is defective in extracellular quinolone signal (PQS) production
  [PMID:12426334 — Gallagher et al. 2002, the IMP source for GO:0044550].

Annotation issue identified

• GO:0016746 acyltransferase activity (IEA, enables) — PqsB has the
  condensing-enzyme (thiolase-like) fold but is catalytically inactive; the
  acyltransferase activity is a property of the PqsBC heterodimer, catalyzed by
  PqsC. Annotating PqsB with enables acyltransferase activity over-attributes the
  catalytic function to the non-catalytic subunit. A contributes_to qualifier (or
  annotation to the complex) would be appropriate. → MARK_AS_OVER_ANNOTATED.

Predicted-complex evidence (BGC project)

Moriwaki et al. (bioRxiv 2025.10.26.684697) predict the PqsB–PqsC heterodimer
(BGC0000922; AAG04386.1/AAG04387.1) at ipTM 0.95, matching PDB 5DWZ.

References

• PMID:24239007 — Dulcey et al. 2013, Chem Biol. VERIFIED.
• PMID:26811339 — Drees et al. 2016, JBC (PqsBC structure, 5DWZ). VERIFIED.
• PMID:12426334 — Gallagher et al. 2002, J Bacteriol (IMP source). VERIFIED.