Interaction of ArmZ with the DNA-binding domain of MexZ induces expression of multidrug efflux pump genes and antimicrobial resistance in .

Multidrug efflux pumps play an important role in antibiotic resistance in bacteria. In , MexXY pump provides intrinsic resistance to many antimicrobials, including aminoglycosides. The expression of operon is negatively regulated by MexZ repressor. The repression is alleviated in response to the antibiotic-induced ribosome stress, which results in increased synthesis of anti-repressor ArmZ, interacting with MexZ. The molecular mechanism of MexZ inactivation by ArmZ is not known. Here, we showed that the N-terminal part of MexZ, encompassing the DNA-binding domain, is required for interaction with ArmZ. Using the bacterial two hybrid system based mutant screening and pull-down analyses we identified substitutions in MexZ that diminished (R3S, K6E, R13H) or completely impaired (K53E) the interaction with ArmZ without blocking MexZ activity as a transcriptional repressor. Introduction of corresponding missense mutations into PAO1161 chromosome impaired ( , ) or blocked ( ) tetracycline mediated induction of expression. Concomitantly, PAO1161 strain was more susceptible to aminoglycosides. The identified residues are highly conserved in MexZ-like transcriptional regulators found in bacterial genomes encoding both MexX/MexY/MexZ and ArmZ/PA5470 orthologs, suggesting that a similar mechanism may contribute to induction of efflux mediated resistance in other bacterial species. Overall, our data shed light on the molecular mechanism of ArmZ mediated induction of intrinsic antimicrobial resistance in .