Rational engineering of photosynthetic electron flux enhances light-powered cytochrome P450 activity

In this study, we exploited a modified photosynthetic electron transfer chain (PET) in the model cyanobacterium Synechococcus PCC 7002, where electrons derived from water-splitting are used to power reactions catalyzed by a heterologous cytochrome P450 (CYP1A1). A simple in vivo fluorescent assay for CYP1A1 activity was employed to determine the impact of rationally engineering of photosynthetic electron flow. This showed that knocking out a subunit of the type I NADH dehydrogenase complex (NDH-1), suggested to be involved in cyclic photosynthetic electron flow (ΔndhD2), can double the activity of CYP1A1, with a concomitant increase in the flux of electrons from photosynthesis. This also resulted in an increase in cellular adenosine triphosphate (ATP) and the ATP/nicotinamide adenine dinucleotide phosphate (NADPH) ratio, suggesting that expression of a heterologous electron sink in photosynthetic organisms can be used to modify the bioenergetic landscape of the cell. We therefore demonstrate that CYP1A1 is limited by electron supply and that photosynthesis can be re-engineered to increase heterologous P450 activity for the production of high-value bioproducts. The increase in cellular ATP achieved could be harnessed to support metabolically demanding heterologous processes. Furthermore, this experimental system could provide valuable insights into the mechanisms of photosynthesis.