Transmembrane topology and histidine protein kinase activity of AgrC, the agr signal receptor in Staphylococcus aureus

Mol Microbiol. 1998 May;28(3):655-62. doi: 10.1046/j.1365-2958.1998.00830.x.


The agr P2 operon in Staphylococcus aureus codes for the elements of a density-sensing cassette made up of a typical two-component signalling system and its corresponding inducer. It is postulated that the autoinducer, a post-translationally modified octapeptide generated from the AgrD peptide, interacts with a receptor protein, coded by agrC, to transmit a signal via AgrA regulating expression of staphylococcal virulence genes through expression of agr RNA III. We show by analysis of PhoA fusions that AgrC is a transmembrane protein, and confirm using Western blotting that a 46 kDa protein corresponding to AgrC is present in the bacterial membrane. This protein is autophosphorylated on a histidine residue only in response to supernatants from an agr+ strain, and can also respond to the purified native octapeptide. A recombinant fusion protein where most of the N-terminal region of AgrC is replaced by the Escherichia coli maltose-binding protein is also autophosphorylated in response to stimulation by agr+ supernatants or purified octapeptide. We conclude that AgrC is the sensor molecule of a typical two-component signal system in S. aureus, and that the ligand-binding site of AgrC is probably located in the third extracellular loop of the protein.

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Binding Sites
  • Blotting, Western
  • Cell Fractionation
  • Gene Expression Regulation, Bacterial
  • Histidine / metabolism*
  • Histidine Kinase
  • Phosphorylation
  • Protein Binding
  • Protein Kinases / chemistry*
  • Protein Kinases / metabolism*
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Recombination, Genetic
  • Signal Transduction
  • Staphylococcus aureus / enzymology*
  • Staphylococcus aureus / genetics
  • Staphylococcus aureus / pathogenicity
  • Trans-Activators*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Virulence / genetics


  • Agr protein, Staphylococcus aureus
  • Bacterial Proteins
  • Recombinant Fusion Proteins
  • Trans-Activators
  • Transcription Factors
  • Histidine
  • Protein Kinases
  • Histidine Kinase