PqsBC, a Condensing Enzyme in the Biosynthesis of the Pseudomonas aeruginosa Quinolone Signal: CRYSTAL STRUCTURE, INHIBITION, AND REACTION MECHANISM

J Biol Chem. 2016 Mar 25;291(13):6610-24. doi: 10.1074/jbc.M115.708453. Epub 2016 Jan 25.


Pseudomonas aeruginosaproduces a number of alkylquinolone-type secondary metabolites best known for their antimicrobial effects and involvement in cell-cell communication. In the alkylquinolone biosynthetic pathway, the β-ketoacyl-(acyl carrier protein) synthase III (FabH)-like enzyme PqsBC catalyzes the condensation of octanoyl-coenzyme A and 2-aminobenzoylacetate (2-ABA) to form the signal molecule 2-heptyl-4(1H)-quinolone. PqsBC, a potential drug target, is unique for its heterodimeric arrangement and an active site different from that of canonical FabH-like enzymes. Considering the sequence dissimilarity between the subunits, a key question was how the two subunits are organized with respect to the active site. In this study, the PqsBC structure was determined to a 2 Å resolution, revealing that PqsB and PqsC have a pseudo-2-fold symmetry that unexpectedly mimics the FabH homodimer. PqsC has an active site composed of Cys-129 and His-269, and the surrounding active site cleft is hydrophobic in character and approximately twice the volume of related FabH enzymes that may be a requirement to accommodate the aromatic substrate 2-ABA. From physiological and kinetic studies, we identified 2-aminoacetophenone as a pathway-inherent competitive inhibitor of PqsBC, whose fluorescence properties could be used forin vitrobinding studies. In a time-resolved setup, we demonstrated that the catalytic histidine is not involved in acyl-enzyme formation, but contributes to an acylation-dependent increase in affinity for the second substrate 2-ABA. Introduction of Asn into the PqsC active site led to significant activity toward the desamino substrate analog benzoylacetate, suggesting that the substrate 2-ABA itself supplies the asparagine-equivalent amino function that assists in catalysis.

Keywords: 2-alkyl-4(1H)-quinolones; FabH; Pseudomonas aeruginosa (P. aeruginosa); Pseudomonas quinolone signal; biosynthesis; condensing enzyme; crystal structure; quorum sensing; secondary metabolism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / antagonists & inhibitors
  • 3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / chemistry*
  • 3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / metabolism
  • 4-Quinolones / chemistry*
  • 4-Quinolones / metabolism
  • Acetophenones / chemistry
  • Acyl Coenzyme A / chemistry*
  • Acyl Coenzyme A / metabolism
  • Amino Acid Sequence
  • Aminobenzoates / chemistry*
  • Aminobenzoates / metabolism
  • Anti-Bacterial Agents / chemistry
  • Bacterial Proteins / antagonists & inhibitors
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Binding Sites
  • Binding, Competitive
  • Biocatalysis
  • Catalytic Domain
  • Crystallography, X-Ray
  • Enzyme Inhibitors / chemistry
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Kinetics
  • Ligands
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding
  • Protein Multimerization
  • Protein Structure, Secondary
  • Protein Subunits / antagonists & inhibitors
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • Pseudomonas aeruginosa / chemistry*
  • Pseudomonas aeruginosa / enzymology
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Sequence Alignment


  • 2-heptyl-4-quinolone
  • 4-Quinolones
  • Acetophenones
  • Acyl Coenzyme A
  • Aminobenzoates
  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Enzyme Inhibitors
  • Ligands
  • Protein Subunits
  • Recombinant Proteins
  • octanoyl-coenzyme A
  • 2-aminoacetophenone
  • 3-ketoacyl-acyl carrier protein synthase III
  • 3-Oxoacyl-(Acyl-Carrier-Protein) Synthase

Associated data

  • PDB/1hnj
  • PDB/2QNZ
  • PDB/3h76
  • PDB/3h77
  • PDB/3h78
  • PDB/5DWZ