Related Experiment Video
Updated: Jun 23, 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 a major driver of multidrug resistance among Gram-negative bacteria. The periplasm provides a distinct environment between the inner and outer membranes of 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 dynamics of the periplasmic adaptor protein, AcrA, and its function within the prototypical AcrAB-TolC multidrug efflux 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 in domain specific organisation in neutral to weakly acidic regimes. We establish a unique histidine residue directs these structural dynamics and is essential for sustaining pump efflux activity across acidic, neutral, and alkaline conditions. Overall, we propose Mg2+ conserves the structural mobility of AcrA to ensure optimal AcrAB-TolC function within rapid changing environments commonly faced by the periplasm during bacterial infection and colonization. This work highlights that Mg2+ is an important mechanistic component in this pump class and possibly across other periplasmic lipoproteins.
Insights
Magnesium ions (Mg2+) stabilize the AcrA protein in Gram-negative bacteria, ensuring the AcrAB-TolC multidrug efflux pump functions effectively across varying pH conditions. This stabilization is crucial for bacterial survival in diverse environments.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Multidrug efflux pumps, like AcrAB-TolC, are critical for Gram-negative bacteria's survival and are a primary cause of multidrug resistance.
- The periplasm, located between bacterial membranes, has a unique ionic and pH environment influenced by external conditions.
Purpose of the Study:
- To investigate the interplay between magnesium ions (Mg2+) and pH in regulating the dynamics and function of the periplasmic adaptor protein AcrA.
- To understand the role of AcrA in the AcrAB-TolC multidrug efflux pump's activity under different environmental conditions.
Main Methods:
- Investigated the structural dynamics of AcrA under varying Mg2+ concentrations and pH levels.
- Identified key residues, specifically a histidine residue, responsible for AcrA's structural modulation.
- Assessed the impact of these dynamics on the overall efflux activity of the AcrAB-TolC pump.
Main Results:
- AcrA exhibits increased flexibility in acidic conditions without Mg2+.
- Mg2+ binding mitigates AcrA's flexibility, promoting specific domain organization in neutral to acidic environments.
- A unique histidine residue was found to direct these structural changes and maintain pump function across a wide pH range.
Conclusions:
- Mg2+ is essential for maintaining AcrA's structural mobility, ensuring the AcrAB-TolC pump's optimal function in dynamic periplasmic environments.
- This Mg2+-mediated regulation is vital for bacterial adaptation during infection and colonization.
- Mg2+ plays a significant mechanistic role in this pump class and potentially other periplasmic lipoproteins.
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