Abstact

The reduction of cytochrome P450 (P450s) is a prerequisite for almost all P450 reactions, where electrons are shuttled to the active site heme from protein electron-transfer (redox) partners. However, this process is more complicated than simple electron transfer due to complex protein-protein interfacial interactions. To improve our understanding of redox partner complexation and selectivity, we investigated ferredoxin interactions with a bacterial P450, CYP108A1 (P450terp), a homologue of the model system, P450cam. We recently solved the crystal structure of the P450terp-substrate complex, and here, we report the crystal structure of terpredoxin (Tdx), the native redox partner of P450terp. Utilizing protein-protein docking and molecular dynamics simulations, we probed possible P450terp-Tdx complexes. Not surprisingly, the surfaces that interact in the P450terp-Tdx complex are the same as in the P450cam-Pdx complex, although the specific interactions are substantially different. Glu38 (E38) in Tdx was predicted to form an ion pair with Arg114 in P450terp, similar to the D38-R112 ion pair in the P450cam-Pdx complex. We therefore prepared an E38L variant of Tdx that lowered but did not eliminate activity. Unlike P450cam, P450terp can be supported by foreign redox partners, including Pdx. Mutations of Pdx designed to mimic Tdx were unable to appreciably increase the turnover rate. To investigate whether redox partner binding could influence structural changes in P450terp, we measured the change in the stability of the P450 oxycomplex in the presence of the ferredoxins with the highest turnover rates and found a correlation between the ferredoxins that enabled turnover and the stability of the oxycomplex.