Cell-free Expressed Bacteriorhodopsin in Different Soluble Membrane Mimetics: Biophysical Properties and NMR Accessibility

SummarySelecting a suitable membrane-mimicking environment is of fundamental importance for the investigation of membrane proteins. Nonconventional surfactants, such as amphipathic polymers (amphipols) and lipid bilayer nanodiscs, have been introduced as promising environments that may overcome intrinsic disadvantages of detergent micelle systems. However, structural insights into the effects of different environments on the embedded protein are limited. Here, we present a comparative study of the heptahelical membrane protein bacteriorhodopsin in detergent micelles, amphipols, and nanodiscs. Our results confirm that nonconventional environments can increase stability of functional bacteriorhodopsin, and demonstrate that well-folded heptahelical membrane proteins are, in principle, accessible by solution-NMR methods in amphipols and phospholipid nanodiscs. Our data distinguish regions of bacteriorhodopsin that mediate membrane/solvent contacts in the tested environments, whereas the protein’s functional inner core remains almost unperturbed. The presented data allow comparing the investigated membrane mimetics in terms of NMR spectral quality and thermal stability required for structural studies.

Graphical AbstractFigure optionsDownload high-quality image (184 K)Download as PowerPoint slideHighlights
► Bacteriorhodopsin (bR) is NMR accessible in nanodiscs and amphipols
► Nonconventional surfactants offer increased stability for cell-free expressed bR
► The bR-membrane interface is highly adaptable in the selected membrane mimetics
► Applications and limitations of the environments for NMR studies are discussed