Differential effects of lipid composition on the thermal and functional properties of membrane associated CYP2J2.

CYP2J2 is a membrane-bound cytochrome P450 that is expressed in cardiomyocytes, where it is known to metabolize arachidonic acid into cardioprotective epoxyeicosatrienoic acids (EETs). It consists of transmembrane domains embedded in the hydrophobic segments of the cell membrane and surrounded by various lipids. Currently, we lack a detailed understanding of the role of specific lipids in mediating the physicochemical properties of CYP2J2 and the factors that govern this phenomenon. In this study, CYP2J2 was reconstituted into nanodiscs with different lipid compositions, selected to reflect those of the endoplasmic reticulum (ER) membrane, where the enzyme is expressed. Using a combination of Nano-Differential Scanning Fluorimetry (nano-DSF) and UV-Visible Spectroscopy, we demonstrate that CYP2J2 undergoes a transition in its unfolding behavior between the detergent micelle and the nanodisc environment, with the first melting transition corresponding to heme perturbation. Furthermore, we show that altering the lipid environment causes shifts of up to 3-4°C and 8-9°C in the first and second melting transition temperatures, respectively, with sphingomyelin- and POPS (1-palmitoyl-2-oleoyl-glycero-3-phosphoserine) containing nanodiscs exhibiting the highest and lowest thermal stabilities, respectively. Lipid composition was found to have no effect on substrate (ebastine) binding affinities. However, NADPH-oxidation rates showed that lipid composition directly affects CYP2J2 function in nanodiscs by altering the rate of electron transfer between the CYP and its redox partner, Cytochrome P450 Reductase (CPR). Fluorescence anisotropy measurements with DPH (1,6-Diphenyl-1,3,5-hexatriene) were also used to characterize the membrane fluidity of cholesterol- and sphingomyelin-containing nanodiscs. Together, the results show that lipid composition directly modulates the thermal stability and functional properties of CYP2J2 in nanodiscs and underscore the importance of the charge of the lipid headgroup and membrane fluidity in our understanding of the mechanism by which lipid composition exerts these effects.