Cryo-EM analyses of the conformational spectrum of an ABC transporter in various membrane mimics

Abstract text (incl. figure legends and references)

Membrane proteins and especially ATP binding cassette (ABC) transporters play a major role in nature. ABC transporters are involved in numerous physiological processes and utilize ATP to translocate various compounds through the lipid bilayer. This process requires large-scale conformational changes and is highly dynamic. Therefore, structure determination is fundamental to understanding these transient proteins' function and mode of action.

Cryo-electron microscopy enables structure determination of proteins in solution to high-resolution and is, therefore, ideally suited to investigate such structural dynamics. However, particles must be extracted from the membrane and stabilized in artificial environments to facilitate cryo-EM sample preparation. To mimic the native environment, components such as detergents or lipid-based systems that form nanodisc can be used.

In this study, we investigated the impact of various hydrophobic environments on the archetypical ABC transporter MsbA which translocates the precursor of Lipopolysaccharide through the inner membrane of gram-negative bacteria.

In addition, to different activity intensities, measured by phosphate release during ATP hydrolysis, we notice a strong bias of the observed conformational spectrum to the respective membrane mimic which complicates the accurate determination of the protein"s behavior.

We hope our experiments can serve as a blueprint to calibrate reconstituted membrane protein systems and are now progressing to an alternative test specimen for validation.