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

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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.
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Document Type: Original Article

Affiliations: 1: UPRES EA1655, Faculté de Médecine Laennec, Rue Guillaume Paradin, 69372 Lyon Cedex 08, France., 2: Skirball Institute of Biomolecular Medicine, New York University Medical Center, New York, NY 10016, USA., 3: Laboratoire d'Immunologie et Biologie Pulmonaire, Hôpital Cardiologique Louis Pradel, BP Lyon Montchat, 69394 Lyon Cedex 03, France.

Publication date: April 1, 1998

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