9.B.46 The Staphylococcus aureus Putative Quorum Sensing Peptide Exporter, AgrB (AgrB) Family
AgrB of Staphylococcus aureus is a 187 aa transmembrane protein with 6 experimentally predicted TMSs. It exhibits proteolytic activity, acting on a precursor quorum sensing autoinducing peptide (AIP), AgrD. It is proposed to export the processed AIP polypeptide.
An operon, agrABCD encodes in addition to AgrB and AgrD, AgrC, a transmembrane sensor kinase, and AgrA, a response regulator. AgrA-P controls the expression of about 20 genes including virulence genes.
AIP is a thiolactone containing a ring of 5 amino acids formed by a thioester linkage between the thiol group in a cysteyl residue and the C-terminal carboxyl group of the peptide; there is a tail of 2-4 amino acyl residues depending on the species. AgrB is proposed to catalyze proteolytic processing, thioester bond formation and secretion. Homologues are found in several species of Staphylococcus as well as species of Clostridium, Listeria and Enterococcus.
The proposed transport reaction catalyzed by AgrB is: