The anti-repressor MecR2 promotes the proteolysis of the mecA repressor and enables optimal expression of β-lactam resistance in MRSA.

Article English OPEN
Pedro Arêde ; Catarina Milheiriço ; Hermínia de Lencastre ; Duarte C Oliveira
  • Publisher: Public Library of Science (PLoS)
  • Journal: PLoS Pathogens, volume 8, issue 7, page e1002816 (issn: 1553-7366, eissn: 1553-7374)
  • Related identifiers: doi: 10.1371/journal.ppat.1002816, pmc: PMC3406092
  • Subject: Cellular Stress Responses | RC581-607 | Research Article | Molecular cell biology | Infectious diseases | Microbial Evolution | Methicillin-resistant Staphylococcus aureus | Staphylococcal infection | Immunologic diseases. Allergy | Bacteriology | Genetics | Bacterial Evolution | Molecular Genetics | Signaling in Cellular Processes | Biology | Signal Transduction | Microbiology | Mechanisms of Signal Transduction | Medicine | QH301-705.5 | Bacterial diseases | Medical Microbiology | DNA transcription | Gene Regulation | Transmembrane Signaling | Gene expression | Biology (General)
    mesheuropmc: bacterial infections and mycoses | biochemical phenomena, metabolism, and nutrition | polycyclic compounds

Methicillin-resistant Staphylococcus aureus (MRSA) is an important human pathogen, which is cross-resistant to virtually all β-lactam antibiotics. MRSA strains are defined by the presence of mecA gene. The transcription of mecA can be regulated by a sensor-inducer (MecR1) and a repressor (MecI), involving a unique series of proteolytic steps. The induction of mecA by MecR1 has been described as very inefficient and, as such, it is believed that optimal expression of β-lactam resistance by MRSA requires a non-functional MecR1-MecI system. However, in a recent study, no correlation was found between the presence of functional MecR1-MecI and the level of β-lactam resistance in a representative collection of epidemic MRSA strains. Here, we demonstrate that the mecA regulatory locus consists, in fact, of an unusual three-component arrangement containing, in addition to mecR1-mecI, the up to now unrecognized mecR2 gene coding for an anti-repressor. The MecR2 function is essential for the full induction of mecA expression, compensating for the inefficient induction of mecA by MecR1 and enabling optimal expression of β-lactam resistance in MRSA strains with functional mecR1-mecI regulatory genes. Our data shows that MecR2 interacts directly with MecI, destabilizing its binding to the mecA promoter, which results in the repressor inactivation by proteolytic cleavage, presumably mediated by native cytoplasmatic proteases. These observations point to a revision of the current model for the transcriptional control of mecA and open new avenues for the design of alternative therapeutic strategies for the treatment of MRSA infections. Moreover, these findings also provide important insights into the complex evolutionary pathways of antibiotic resistance and molecular mechanisms of transcriptional regulation in bacteria.
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