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Updated: Jun 2, 2025
In vitro Investigation of the MexAB Efflux Pump From Pseudomonas aeruginosa
Published on: February 17, 2014
Mg2+-dependent mechanism of environmental versatility in a multidrug efflux pump
Benjamin Russell Lewis1, Muhammad R Uddin2, Katie M Kuo3
1Department of Chemistry, Britannia House, 7 Trinity Street, King's College London, London, SE1 1DB, UK.
Abstract:
Tripartite resistance nodulation and cell division multidrug efflux pumps span the periplasm and are major drivers of multidrug resistance among gram-negative bacteria. Cations, such as Mg2+, become concentrated within the periplasm and, in contrast to the cytoplasm, its pH is sensitive to conditions outside the cell. Here, we reveal an interplay between Mg2+ and pH in modulating the structural dynamics of the periplasmic adapter protein, AcrA, and its function within the prototypical AcrAB-TolC multidrug pump from Escherichia coli. In the absence of Mg2+, AcrA becomes increasingly plastic within acidic conditions, but when Mg2+ is bound this is ameliorated, resulting instead in domain specific organization. We establish a unique histidine residue directs these dynamics and is essential for sustaining pump activity across acidic, neutral, and basic regimes. Overall, we propose Mg2+ conserves AcrA structural mobility to ensure optimal AcrAB-TolC function within rapidly changing environments commonly faced during bacterial infection and colonization.
Insights
Magnesium ions (Mg2+) and pH regulate the structure and function of the AcrA protein in multidrug efflux pumps. This regulation ensures bacterial multidrug resistance pumps work effectively in changing environments during infection.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Tripartite multidrug efflux pumps are key to multidrug resistance in Gram-negative bacteria.
- The periplasmic adapter protein AcrA is crucial for pump assembly and function.
- Periplasmic Mg2+ concentration and pH can fluctuate, potentially impacting pump activity.
Purpose of the Study:
- To investigate the interplay between Mg2+ and pH in modulating AcrA structure and function.
- To understand how AcrA maintains multidrug pump activity across different environmental conditions.
Main Methods:
- Structural analysis of AcrA under varying Mg2+ and pH conditions.
- Functional assays to assess multidrug pump activity.
- Site-directed mutagenesis to identify key residues involved in Mg2+ binding and pH sensitivity.
Main Results:
- Mg2+ binding stabilizes AcrA structure, preventing excessive plasticity in acidic conditions.
- A specific histidine residue in AcrA is critical for maintaining pump function across a range of pH.
- AcrA's structural dynamics are modulated by Mg2+ and pH, influencing overall pump efficiency.
Conclusions:
- Mg2+ plays a vital role in conserving AcrA's structural mobility, ensuring optimal AcrAB-TolC pump function.
- This Mg2+-mediated regulation is essential for bacterial survival in dynamic environments during infection and colonization.
- Understanding these mechanisms offers potential targets for combating multidrug resistance.
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