Binding and Electron Transfer between Putidaredoxin and Cytochrome P450cam. Theory and Experiments

We present a detailed atomic level view of the interactions between cytochrome P450cam (CYP101) and its natural redox partner, putidaredoxin (Pdx). A combined theoretical (Poisson−Boltzmann electrostatic calculations, electron transfer pathways, and molecular dynamics) and experimental (site-directed mutagenesis and kinetic analysis) study is used to pinpoint surface residues in both proteins that are important for electron transfer, binding, or both. We find a situation where the electrostatically complementary regions at the surface of both proteins overlap strongly with regions that have large electron transfer couplings to the redox centers. This means that a small surface patch in each protein is involved in binding and electron transfer. A dominant electron transfer pathway is identified, corresponding to an electron leaving the reduced Fe2S2 in Pdx, going through Cys39 and Asp38, and transferring across the interprotein interface to Arg112 (CYP101), then to a heme propionate group, and finally to the heme iron center.