Identification of ligand specificity determinants in AgrC, the Staphylococcus aureus quorum-sensing receptor

Edward Geisinger, Elizabeth A. George, Tom W. Muir, Richard P. Novick

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71 Scopus citations


Activation of the agr system, a major regulator of staphylococcal virulence, is initiated by the binding of a specific autoinducing peptide (AIP) to the extracellular domain of AgrC, a classical receptor histidine protein kinase. There are four known agr specificity groups in Staphylococcus aureus, and we have previously localized the determinant of AIP receptor specificity to the C-terminal half of the AgrC sensor domain. We have now identified the specific amino acid residues that determine ligand activation specificity for agr groups I and IV, the two most closely related. Comparison of the AgrC-I and AgrC-IV sequences revealed a set of five divergent residues in the region of the second extracellular loop of the receptor that could be responsible. Accordingly, we exchanged these residues between AgrC-I and AgrC-IV and tested the resulting constructs for activation by the respective AIPs, measuring activation kinetics with a transcriptional fusion of blaZ to the principal agr promoter, P3. Exchange of all five residues caused a complete switch in receptor specificity. Replacement of two of the AgrC-IV residues by the corresponding residues in AgrC-I caused the receptor to be activated by AIP-I nearly as well as the wild type AgrC-I receptor. Replacement of two different AgrC-I residues by the corresponding AgrC-IV residues broadened receptor recognition specificity to include both AIPs. Various types of intermediate activity were observed with other replacement mutations. Preliminary characterization of the AgrC-IAIP-I interaction suggests that ligand specificity may be sterically determined.

Original languageEnglish (US)
Pages (from-to)8930-8938
Number of pages9
JournalJournal of Biological Chemistry
Issue number14
StatePublished - Apr 4 2008
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Molecular Biology
  • Biochemistry
  • Cell Biology


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