The study, published in the leading journal Nature Microbiology, has unravelled how the AcrAB-TolC efflux pump, found on the outer membrane of many bacteria, changes its shape to export drugs and provide resistance.
The international team used cryo-electron microscopy to image the atomic structure of the pump, providing the long-sought answer on how it opens to allow the efflux of antibiotics.
Understanding the mechanism of the AcrAB-TolC pump opens the way to potential treatments that could reverse bacterial drug resistance.
The bacterial pump consists of the membrane fusion protein, AcrA, the multidrug transporter, AcrB, and the outer membrane channel, TolC.
AcrB contains two funnel-like compartments that bind and export the antibiotics.
When antibiotics enter the first compartment, the funnel changes shape, which enables the antibiotics to be passed onto the second funnel for export from the cell.
To understand the structural changes needed to pump drugs out of the cell, the researchers used nanodiscs, which are tiny discs of lipid membrane, to stabilise the different components of the pump in their native environment.
They found a series of intermediates revealing how the two compartments of AcrB deform to allow antibiotics to be moved from one funnel to the other.
Professor Michelle Chang from the ANU Research School of Chemistry and ARC Centre of Excellence in Advanced Molecular Imaging, said: "The AcrAB-TolC pump is notoriously difficult to study because of its dynamic nature and instability when removed from the cell membrane.
"Being able to generate stable intermediates, and observe the structural changes in real time using cryo-EM, has enabled us to understand the mechanism of the pump like never before.
"This opens the potential to inhibit its function and block the efflux of antibiotics, essentially restoring the effectiveness of the drugs."
Dr Emma Taylor from the ANU Research School of Chemistry said: "Using nanodiscs has enabled us to gain new insights into how such membrane protein complexes work.
"This study not only provides a wealth of knowledge on this particular pump complex, it also introduces methodologies that can be applied to a wide range of multi-component membrane proteins."
The research team included scientists from the ANU, the University of Melbourne and the University of Illinois at Chicago.
