Conformational equilibrium defines the variable induction of the multidrug-binding transcriptional repressor QacR

Abstract

QacR, a multidrug-binding transcriptional repressor in pathogenic bacteria Staphylococcus aureus, modulates the transcriptional level of the multidrug transporter gene, qacA, in response to engaging a set of diverse ligands. However, the structural basis that defines the variable induction level remains unknown. Here, we reveal that the conformational equilibrium between the repressive and inducive conformations in QacR defines the induction level of the transporter gene. In addition, the unligated QacR is already partly populated in the inducive conformation, allowing the basal expression of the transporter. We also showed that, in the known constitutively active QacR mutants, the equilibrium is shifted more toward the inducive conformation, even in the unligated state. These results highlight the unexpected structural mechanism, connecting the promiscuous multidrug binding to the variable transcriptional regulation of QacR, which provide clues to dysfunctioning of the multidrug resistance systems.

The two-Cys-type TetR repressor GbaA confers resistance under disulfide and electrophile stress in Staphylococcus aureus

“…A main feature of the E. coli AcrR structure is the presence of a large cavity in the ligand binding pocket, which was shown to accommodate many different ligands, such as ethidium bromide, proflavin, and rhodamine 6G and ciprofloxacin to inhibit DNA binding activity [ 49 , 52 ]. Similarly, the multidrug efflux pump regulator QacR of S. aureus responds to many cationic lipophilic antiseptics and disinfectants, such as rhodamine 6G, crystal violet, palmatine, nitidine as well as antimicrobial plant alkaloids [ [53] , [54] , [55] ]. However, QacR and AcrR control multidrug resistance via their specific efflux pumps, which is not the case for GbaA.…”

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

“…The activities of many regulators of the efflux pumps are frequently affected by the substrates that will be transported by the regulated efflux pump [166][167][168][169][170]. These regulators usually contain a drug-binding pocket within the ligand-binding domain, and the binding of the drug to these regulators modulates their transcriptional repressor/activator activities [171][172][173][174].…”

Stress response modulation: the key to survival of pathogenic and spoilage bacteria during poultry processing

“…This gene pair regulates aminoglycoside resistance in Methicillin Resistant S. aureus (MRSA) [106,108]. This plasmid is also associated with resistance to QAC sanitizers and other antimicrobial compounds [38,106]. The Major Facilitator Superfamily (MFS)-type efflux pump gene qacA is carried on the same plasmid alongside genes responsible for cell membrane and cell wall alterations that confer further resistance to antimicrobial compounds [109,110].…”

“…Under normal conditions, the dimeric QacR protein binds to Intergenic Region 1, which overlaps with the qacA promoter region, and prevents most transcription of the efflux system gene. However, QacR can be bound by a broad range of QACs and related compounds due to the plasticity of the substrate binding site, leading to a conformational change in the repressive protein [38]. The efflux pump protein QacA and its homologs, as well as adjacent QAC-tolerance determinant genes such as those responsible for membrane adaptations, can then be expressed to extrude cytoplasmic QACs, and so the stress can be viewed as directly increasing the tolerance of the cell to these compounds [39].…”