Molecular basis for multidrug efflux by an anaerobic RND transporter

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Bacteria utilize efflux pumps to survive harsh environments, such as low oxygen, extreme pH, and nutrient scarcity.
• The MdtEF efflux pump, part of the resistance-nodulation-cell division (RND) superfamily, is upregulated under these stress conditions, but its mechanism remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanism of the Escherichia coli MdtEF multidrug transporter.
• To understand how MdtEF contributes to bacterial resistance against toxic substances and antibiotics in challenging ecological niches.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structures of MdtF in native-lipid nanodiscs.
• Structures included a single-point mutant and substrate-bound forms to analyze drug binding and transport.

Main Results:

• The study identified conformational plasticity in the drug binding domain and channel, explaining the pump's broad substrate specificity.
• Distinct transmembrane state transitions and an enhanced proton relay network were observed in MdtF.
• An acid-responsive increase in efflux efficiency was discovered, alongside altered drug transport allostery.

Conclusions:

• The findings reveal how MdtEF's structural flexibility and proton relay network enable efficient xenobiotic and metabolite disposal.
• This mechanism provides bacteria with enhanced survival strategies against acid stress and toxic compounds, particularly in the gastrointestinal tract.