Cryo-Electron Microscopy Structure of an Acinetobacter baumannii Multidrug Efflux Pump

Area of Science:

• Structural Biology
• Microbiology
• Biochemistry

Background:

• Acinetobacter baumannii is a major cause of hospital-acquired infections and exhibits high levels of antibiotic resistance.
• Multidrug efflux pumps are key contributors to antibiotic resistance in A. baumannii, facilitating the removal of various drugs from bacterial cells.
• The AdeB pump, a member of the resistance-nodulation-cell division (RND) family, is a trimeric membrane protein crucial for multidrug extrusion.

Purpose of the Study:

• To determine the high-resolution structure of the Acinetobacter baumannii AdeB multidrug efflux pump.
• To elucidate the mechanism of proton-coupled drug efflux and energy coupling in AdeB.
• To provide a structural basis for developing novel strategies to combat multidrug resistance.

Main Methods:

• Single-particle cryo-electron microscopy (cryo-EM) was employed to visualize the AdeB pump.
• The AdeB pump was reconstituted into lipidic nanodiscs for structural analysis.
• High-resolution structural data was obtained to 2.98 Å.

Main Results:

• The cryo-EM structure of the trimeric AdeB efflux pump was determined at 2.98 Å resolution.
• In the absence of substrates, each AdeB protomer was observed in a resting conformational state.
• A plausible pathway for multidrug extrusion and a mechanism for energy coupling were proposed.

Conclusions:

• The structural data reveals the resting state conformation of the AdeB pump, offering insights into its function.
• Proton influx and drug efflux are likely synchronized and coordinated within the AdeB transport cycle.
• This study provides a foundation for structure-guided drug design to overcome multidrug resistance in A. baumannii.