Effector Roles of Putidaredoxin on Cytochrome P450cam Conformational States

In this study, the effector role of Pdx (putidaredoxin) on cytochrome P450cam conformation is refined by attaching two different spin labels, MTSL or BSL (bifunctional spin-label) onto the F or G helices and using DEER (double electron-electron resonance) to measure the distance between labels. Recent EPR and crystallographic studies have observed that oxidized Pdx induces substrate-bound P450cam to change from the closed to the open state. However, this change was not observed by DEER in the reduced Pdx complex with carbon-monoxide-bound P450cam (Fe(2+)CO). In addition, recent NMR studies have failed to observe a change in P450cam conformation upon binding Pdx. Hence, resolving these issues is important for a full understanding the effector role of Pdx. Here we show that oxidized Pdx induces camphor-bound P450cam to shift from the closed to the open conformation when labeled on either the F or G helices with MTSL. BSL at these sites can either narrow the distance distribution widths dramatically or alter the extent of the conformational change. In addition, we report DEER spectra on a mixed oxidation state containing oxidized Pdx and ferrous CO-bound P450cam, showing that P450cam remains closed. This indicates that CO binding to the heme prevents P450cam from opening, overriding the influence exerted by Pdx binding. Finally, we report the open form P450cam crystal structure with substrate bound, which suggests that crystal packing effects may prevent conformational conversion. Using multiple labeling approaches, DEER provides a unique perspective to resolve how the conformation of P450cam depends on Pdx and ligand states.