Small angle scattering reveals the orientation of cytochrome P450 19A1 in lipoprotein nanodiscs.

Human aromatase (CYP19A1), the cytochrome P450 enzyme responsible for conversion of androgens to estrogens, was incorporated into lipoprotein nanodiscs (NDs) and interrogated by small angle X-ray and neutron scattering (SAXS/SANS). CYP19A1 was associated with the surface and centered at the edge of the long axis of the ND membrane. In the absence of the N-terminal anchor, the amphipathic A'- and G'-helices were predominately buried in the lipid head groups, with the possibly that their hydrophobic side chains protrude into the hydrophobic, aliphatic tails. The prediction is like that for CYP3A4 based on SAXS employing a similar modeling approach. The orientation of CYP19A1 in a ND is consistent with our previous predictions based on molecular dynamics simulations and lends additional credibility to the notion that CYP19A1 captures substrates from the membrane.