Mutations in MexB that affect the efflux of antibiotics with cytoplasmic targets

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Pseudomonas aeruginosa utilizes MexAB-OprM efflux pumps for multidrug resistance.
• Inner membrane protein MexB plays a key role in substrate recognition within the MexAB-OprM system.
• Existing research primarily focuses on the periplasmic domains of RND transporters, leaving cytoplasmic regions less understood.

Purpose of the Study:

• To investigate the role of conserved phenylalanine residues in the cytoplasmic region of MexB.
• To determine the impact of specific mutations on MexB's drug interaction and efflux capabilities.
• To identify potential novel drug-binding sites within RND transporters.

Main Methods:

• Site-directed mutagenesis was used to create the FAFA MexB mutant.
• Cytotoxicity assays were performed to assess the interaction of wild-type and mutant MexB with various drugs.
• Drug transport assays were conducted to evaluate the efflux activity of the modified protein.

Main Results:

• The FAFA mutation in MexB specifically impacted the efflux of intracellularly targeted compounds.
• Efflux of cell wall synthesis inhibitors and membrane probes remained unaffected by the FAFA mutation.
• These findings suggest the existence of a previously unrecognized cytoplasmic-binding site in RND transporters.

Conclusions:

• The study identifies a novel cytoplasmic-binding site in RND drug efflux transporters.
• Understanding this site is crucial for deciphering drug resistance mechanisms in Gram-negative bacteria.
• This research provides new insights into the molecular basis of multidrug resistance.