Probing the transmembrane structure and dynamics of microsomal NADPH-cytochrome P450 oxidoreductase by solid-state NMR.

NADPH-cytochrome P450 oxidoreductase (CYPOR) is an essential redox partner of the cytochrome P450 (cyt P450) superfamily of metabolic enzymes. In the endoplasmic reticulum of liver cells, such enzymes metabolize ~75% of the pharmaceuticals in use today. It is known that the transmembrane domain of CYPOR plays a crucial role in aiding the formation of a complex between CYPOR and cyt P450. Here we present the transmembrane structure, topology, and dynamics of the FMN binding domain of CYPOR in a native membrane-like environment. Our solid-state NMR results reveal that the N-terminal transmembrane domain of CYPOR adopts an α-helical conformation in the lipid membrane environment. Most notably, we also show that the transmembrane helix is tilted ~13° from the lipid bilayer normal, and exhibits motions on a submillisecond timescale including rotational diffusion of the whole helix and fluctuation of the helical director axis. The approaches and the information reported in this study would enable further investigations on the structure and dynamics of the full-length NADPH-cytochrome P450 oxidoreductase and its interaction with other membrane proteins in a membrane environment.