AIP System

• autoinducing peptides (AIP) are produced by gram positive bacteria

  
• AIP in gram positive bacteria are genetically encoded by agrD gene in S. aureus bacteria
• agrD gene and AIP production in gram positive bacteria

  • AIP transcribed and translated into linear peptide by AgrD gene -> AIP cyclized and exported by AgrB transporter -> AIP binds AgrC receptor kinase -> AgrC kinase autophosphorylates then transfers phosphate to AgrA response regulator -> AgrA becomes TF and binds DNA to turn on agr operon and RNAIII

  
• RNAIII gene transcribes for repression of Rot (repressor of toxin) which indirectly activates virulence genes
• RNAIII is a small RNA molecule that binds and inhibits the transcriptional regulator Rot,

  • if no AIP/Agr signals -> Rot represses virulence factors
  • upon infection and quorum -> AIP/Agr signals are produced and RNAIII expression increases thus Rot gets repressed and virulence thrives in host

  
• Agr operon controls virulence factor production in S. aureus
• AIP from different bacterial strains can inhibit unrelated AgrC sensors which prevents the Agr signalling cascade from occurring because each AIP has a different amino acid sequence

  
• AIP inhibitors of 1 strain can be used as probiotics to shut down AIP systems in other bacterial strains while it simultaneously stimulates itself