Mutations affecting DNA-binding activity of the MexR repressor of mexR-mexA-mexB-oprM operon expression

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• MexR is a transcriptional repressor regulating genes involved in multidrug resistance.
• Understanding MexR's DNA-binding mechanism is crucial for developing strategies to combat antibiotic resistance.

Purpose of the Study:

• To investigate the specific regions of the MexR protein responsible for binding to the mexOP DNA sequence.
• To elucidate the structural determinants of DNA-DNA binding in MexR.

Main Methods:

• Isolation and characterization of 25 MexR mutants.
• Assessment of dimerizing ability and mexOP DNA binding capability for each mutant.
• Analysis of mutation locations within the MexR protein structure.

Main Results:

• 25 MexR mutants were successfully isolated.
• All mutants retained their dimerizing ability.
• 20 out of 25 mutants lost the ability to bind mexOP DNA.
• The majority of mutations affecting DNA binding were located in the hydrophobic core region (alpha4, W1, alpha2, alpha3, and beta2).
• Only 3 mutations were found in positively charged residues.

Conclusions:

• DNA binding by MexR is mediated by distinct regions within the protein.
• The hydrophobic core region of the DNA-binding domain plays a critical role in MexR's interaction with mexOP DNA.
• These findings provide insights into the structural basis of transcriptional regulation by MexR.