Strengthening NADPH Regeneration for Improving Photo-biocatalytic Ketones Asymmetric Reduction Reaction by Synechocystis Through Overexpression of FNR

Microalgae are excellent biocatalyst candidates for photo-biocatalytic-asymmetric reduction of prochiral ketones to produce enantiomer alcohols. In the biocatalysis asymmetric reduction of carbonyl group process, the cofactor, NADPH, plays a key role. So the current study focused on the effect of NADPH availability on the reduction. Photosynthesis is a main pathway for NADPH regeneration in microalgae, and the ferredoxin-NADP+ oxidoreductase (FNR) is the key enzyme in this process. In this work, we constructed an engineered cyanobacterium Synechocystis sp. PCC6803::Ω-PpetE-petH to overexpress FNR gene petH to strengthen NADPH regeneration. The results show that the intracellular NADPH content was increased 80.8% compared to the wild type. Applying the Synechocystis sp. PCC6803::Ω-PpetE-petH to catalyze the model asymmetric reduction reaction (reduction of acetophenone to S-phenylethanol), the yield was improved 61.2% compared to the wild-type. This work makes the microalgal biocatalysis asymmetric reduction process become more preponderant via providing a new route to enhance the regeneration of cofactor NADPH. Putative metabolic process of nicotinamide adenine dinucleotide phosphate (NADPH) regeneration and the photo-biocatalytic-asymmetric reduction reaction of prochiral ketones in microalgal cells.