title: Site-specific mutation of Staphylococcus aureus VraS reveals a crucial role for the VraR-VraS sensor in the emergence of glycopeptide resistance.
abstract: An initial response of Staphylococcus aureus to encounter with cell wall-active antibiotics occurs by transmembrane signaling systems that orchestrate changes in gene expression to promote survival. Histidine kinase two-component sensor-response regulators such as VraRS contribute to this response. In this study, we examined VraS membrane sensor phosphotransfer signal transduction and explored the genetic consequences of disrupting signaling by engineering a site-specific vraS chromosomal mutation. We have used in vitro autophosphorylation assay with purified VraS[64-347] lacking its transmembrane anchor region and tested site-specific kinase domain histidine mutants. We identified VraS H156 as the probable site of autophosphorylation and show phosphotransfer in vitro using purified VraR. Genetic studies show that the vraS(H156A) mutation in three strain backgrounds (ISP794, Newman, and COL) fails to generate detectable first-step reduced susceptibility teicoplanin mutants and severely reduces first-step vancomycin mutants. The emergence of low-level glycopeptide resistance in strain ISP794, derived from strain 8325 (ΔrsbU), did not require a functional σ(B), but rsbU restoration could enhance the emergence frequency supporting a role for this alternative sigma factor in promoting glycopeptide resistance. Transcriptional analysis of vraS(H156A) strains revealed a pronounced reduction but not complete abrogation of the vraRS operon after exposure to cell wall-active antibiotics, suggesting that additional factors independent of VraS-driven phosphotransfer, or σ(B), exist for this promoter. Collectively, our results reveal important details of the VraRS signaling system and predict that pharmacologic blockade of the VraS sensor kinase will have profound effects on blocking emergence of cell wall-active antibiotic resistance in S. aureus.
authors.affiliation: Service of Infectious Diseases, University Hospital and Medical School of Geneva, 4 rue Gabrielle-Perret-Gentil, CH-1211 Geneva 14, Switzerland.
authors.forename: Elena
authors.initials: E
authors.lastname: Galbusera
authors.forename: Adriana
authors.initials: A
authors.lastname: Renzoni
authors.forename: Diego O
authors.initials: DO
authors.lastname: Andrey
authors.forename: Antoinette
authors.initials: A
authors.lastname: Monod
authors.forename: Christine
authors.initials: C
authors.lastname: Barras
authors.forename: Paolo
authors.initials: P
authors.lastname: Tortora
authors.forename: Alessandra
authors.initials: A
authors.lastname: Polissi
authors.forename: William L
authors.initials: WL
authors.lastname: Kelley
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015152:Blotting, Northern; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006020:Glycopeptides / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D016133:Polymerase Chain Reaction; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D006020:Glycopeptides; C478170:VraR protein, Staphylococcus aureus; C478169:VraS protein, Staphylococcus aureus