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 Fe 2 S 2 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.