Structural characterization of the EmrAB-TolC efflux complex from E. coli.

Area of Science:

• Structural Biology
• Microbiology
• Biochemistry

Background:

• Gram-negative bacteria utilize tripartite multidrug efflux systems for exporting antimicrobial compounds.
• These systems span both bacterial membranes, comprising inner membrane transporters, outer membrane channels, and periplasmic adaptors.

Purpose of the Study:

• To determine the structure of the Escherichia coli EmrAB-TolC tripartite efflux system.
• To gain insights into the mechanism of antimicrobial compound export via this Major Facilitator Superfamily (MSF) system.

Main Methods:

• Co-expression and purification of the EmrAB-TolC complex.
• Stabilization of the complex using Amphipol polymer.
• Analysis of the complex structure using electron microscopy.

Main Results:

• The complete 33 nm long EmrAB-TolC complex was visualized.
• Electron microscopy revealed an extended periplasmic canal formed by the outer membrane protein TolC and periplasmic adaptor EmrA.
• A probable tip-to-tip interaction between EmrA and TolC was observed, elucidating the connection to the inner membrane transporter EmrB.

Conclusions:

• The study provides the first structural insights into the entire EmrAB-TolC efflux system.
• The findings elucidate the role of adaptor proteins in connecting inner and outer membrane components for efficient drug efflux.
• The structural data contributes to understanding multidrug resistance mechanisms in Gram-negative bacteria.