Timing is everything – impact of naturally occurring Staphylococcus aureus AgrC cytoplasmic domain adaptive mutations on auto-induction

Mutations in the polymorphic Staphylococcus aureus agr locus responsible for quorum sensing (QS) dependent virulence gene regulation occur frequently during host adaptation. In two genomically closely related S. aureus clinical isolates exhibiting marked differences in Pantone-Valentin leukocidin production, a mutation conferring an N267I substitution was identified in the cytoplasmic domain of the QS sensor kinase, AgrC. This natural mutation delayed the onset and accumulation of auto-inducing peptide (AIP) and showed reduced responsiveness to exogenous AIPs. Other naturally occurring S. aureus AgrC cytoplasmic domain mutations were identified including T247I, I311T, A343T, L245S and F264C. These mutations were associated with reduced cytotoxicity, delayed/reduced AIP production and impaired sensitivity to exogenous AIP. Molecular dynamics simulations were used to model the AgrC conformational changes arising. Structural changes in the key functional subdomains involved in dimerization, ATP binding, auto-phosphorylation and phosphotransfer were observed. These appear to increase the threshold for agr activation via AIP-dependent autoinduction so reducing virulence and maintaining S. aureus in the 'colonization' mode. Understanding how the timing of agr activation determines virulence potential in vivo will aid our understanding of the role played by QS during staphylococcal infections and help inform the development of targeted anti-virulence therapies.