Molecular basis for multidrug efflux by an anaerobic-associated RND transporter

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Bacteria possess resistance mechanisms to survive challenging environments like low oxygen, extreme acidity, and nutrient scarcity.
• The resistance-nodulation-cell division (RND) superfamily includes efflux pumps like MdtEF, crucial for bacterial survival but with an unknown molecular mechanism.

Purpose of the Study:

• To elucidate the molecular mechanism of the MdtF efflux pump, a proton motive force-driven transporter.
• To investigate the structural basis for MdtF's role in bacterial resistance under specific environmental stresses.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structures of Escherichia coli MdtF.
• Structures were obtained in native-lipid nanodiscs, including a single-point mutant and substrate-bound forms.

Main Results:

• Distinct transmembrane state transitions were observed in MdtF, enhancing the proton relay network.
• Conformational plasticity in the drug binding domain and channel influences substrate polyspecificity.
• An acid-responsive increase in efflux efficiency and altered drug transport allostery were identified.

Conclusions:

• MdtF exhibits unique transmembrane transitions and allosteric regulation, contributing to its function.
• The findings provide mechanistic insights into bacterial xenobiotic and toxin removal, particularly in the gastrointestinal tract under acid stress.