The PhoQ histidine kinases of Salmonella and Pseudomonas spp. are structurally and functionally different: evidence that pH and antimicrobial peptide sensing contribute to mammalian pathogenesis

Mol Microbiol. 2008 Jul;69(2):503-19. doi: 10.1111/j.1365-2958.2008.06303.x.


The PhoQ sensor kinase is essential for Salmonella typhimurium virulence for animals, and a homologue exists in the environmental organism and opportunistic pathogen Pseudomonas aeruginosa. S. typhimurium PhoQ (ST-PhoQ) is repressed by millimolar concentrations of divalent cations and activated by antimicrobial peptides and at acidic pH. ST-PhoQ has a periplasmic Per-ARNT-Sim domain, a fold commonly employed for ligand binding. However, substrate binding is instead accomplished by an acidic patch in the periplasmic domain that interacts with the inner membrane through divalent cation bridges. The DNA sequence encoding this acidic patch is absent from Pseudomonas phoQ (PA-PhoQ). Here, we demonstrate that PA-PhoQ binds and is repressed by divalent cations, and can functionally complement a S. typhimurium phoQ-null mutant. Mutational analysis and NMR spectroscopy of the periplasmic domains of ST-PhoQ and PA-PhoQ indicate distinct mechanisms of binding divalent cation. The data are consistent with PA-PhoQ binding metal in a specific ligand-binding pocket. PA-PhoQ was partially activated by acidic pH but not by antimicrobial peptides. S. typhimurium expressing PA-PhoQ protein were attenuated for virulence in a mouse model, suggesting that the ability of Salmonella to sense host environments via antimicrobial peptides and acidic pH is an important contribution to pathogenesis.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antimicrobial Cationic Peptides / metabolism
  • Bacterial Proteins / antagonists & inhibitors
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Binding Sites
  • Cations, Divalent / metabolism
  • DNA Mutational Analysis
  • Female
  • Gene Deletion
  • Genetic Complementation Test
  • Histidine Kinase
  • Hydrogen-Ion Concentration
  • Magnetic Resonance Spectroscopy
  • Mice
  • Mice, Inbred BALB C
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding
  • Protein Kinases / chemistry
  • Protein Kinases / metabolism
  • Pseudomonas aeruginosa / chemistry*
  • Pseudomonas aeruginosa / enzymology*
  • Salmonella Infections, Animal / microbiology
  • Salmonella typhimurium / chemistry*
  • Salmonella typhimurium / enzymology*
  • Salmonella typhimurium / pathogenicity
  • Sequence Alignment
  • Virulence


  • Antimicrobial Cationic Peptides
  • Bacterial Proteins
  • Cations, Divalent
  • PhoQ protein, Bacteria
  • Protein Kinases
  • Histidine Kinase