Membrane-Anchored Cytochrome P450 1A2-Cytochrome b5 Complex Features an X-Shaped Contact between Antiparallel Transmembrane Helices

Eukaryotic cytochromes P450 (P450) are membrane-bound enzymes oxidizing a broad spectrum of hydrophobic substrates, including xenobiotics. Protein protein interactions play a critical role in this process. In particular, the formation of transient complexes of P450 with another protein of the endoplasmic reticulum membrane, cytochrome b(5) (cyt b(5)), dictates catalytic activities of several P450s. To lay a structural foundation for the investigation of these effects, we constructed a model of the membrane-bound full-length human P450 1A2-cyt b(5) complex. The model was assembled from several parts using a multiscale modeling approach covering all-atom and coarse grained molecular dynamics (MD). For soluble P450 1A2-cyt b(5) complexes, these simulations yielded three stable binding modes (sA(I), sA(II), and sB). The membrane-spanning transmembrane domains were reconstituted with the phospholipid bilayer using self-assembly MD. The predicted full-length membrane-bound complexes (mAI and mB) featured a spontaneously formed X-shaped contact between antiparallel transmembrane domains, whereas the mA,, mode was found to be unstable in the membrane environment. The mutual position of soluble domains in binding mode mA(I) was analogous to the sA(I) complex. Featuring the largest contact area, the least structural flexibility, the shortest electron transfer distance, and the highest number of interprotein salt bridges, mode mA(I) is the best candidate for the catalytically relevant full-length complex.