The lipid bilayer modulates the structure and function of an ATP-binding cassette exporter [Membrane Biology]

January 2nd, 2016 by Zoghbi, M. E., Cooper, R. S., Altenberg, G. A.

ATP-binding cassette (ABC) exporters use the energy of ATP hydrolysis to transport substrates across membranes by switching between inward- and outward-facing conformations. Essentially all structural studies of these proteins have been performed with the proteins in detergent micelles, locked in specific conformations and/or at low temperature. Here, we used luminescence resonance energy transfer (LRET) spectroscopy to study the prototypical ABC exporter MsbA reconstituted in nanodiscs,at 37°C, and while it performs ATP hydrolysis. We found major differences when comparing MsbA in these native-like conditions with double electron-electron resonance data and the crystal structure of MsbA in the open inward-facing conformation. The most striking differences include a significantly smaller separation between the nucleotide-binding domains and a larger fraction of molecules with associated nucleotide-binding domains in the nucleotide-free apo state. These studies stress the importance of studying membrane proteins in an environment that approaches physiological conditions.