An Active and Versatile Electron Transport System for Cytochrome P450 Monooxygenases from the Alkane Degrading...

Cytochrome P450 monooxygenases (CYPs) are valuable biocatalysts for the oxyfunctionalization of non-activated carbon-hydrogen bonds. Most CYPs rely on electron transport proteins as redox partners. In this study, the ferredoxin reductase (FdR) and ferredoxin (FD) for a cytochrome P450 monooxygenase from Acinetobacter sp. OC4 are investigated. Upon heterologous production of both proteins independently in Escherichia coli, spectral analysis showed their reduction capability towards reporter electron acceptors, e. g., cytochrome c. The individual proteins' specific activity towards cytochrome c reduction was 25 U mg^-1. Furthermore, the possibility to enhance electron transfer by artificial fusion of the units was elucidated. FdR and FD were linked by helical linkers [EAAAK]_n, flexible glycine linkers [GGGGS]_n or rigid proline linkers [EPPPP]_n of n=1-4 sequence repetitions. The system with a glycine linker (n=4) reached an appreciable specific activity of 19 U mg^-1 towards cytochrome c. Moreover, their ability to drive different members of the CYP153A subfamily is demonstrated. By creating artificial self-sufficient P450s with FdR, FD, and a panel of four CYP153A representatives, effective hydroxylation of n-hexane in a whole-cell system was achieved. The results indicate this protein combination to constitute a functional and versatile surrogate electron transport system for this subfamily.