Shifting redox reaction equilibria on demand using an orthogonal redox cofactor

Nature's two redox cofactors, nicotinamide adenine dinucleotide (NAD⁺) and nicotinamide adenine dinucleotide phosphate (NADP⁺), are held at different reduction potentials, driving catabolism and anabolism in opposite directions. In biomanufacturing, there is a need to flexibly control redox reaction direction decoupled from catabolism and anabolism. We established nicotinamide mononucleotide (NMN⁺) as a noncanonical cofactor orthogonal to NAD(P)⁺. Here we present the development of Nox Ortho, a reduced NMN⁺ (NMNH)-specific oxidase, that completes the toolkit to modulate NMNH:NMN⁺ ratio together with an NMN⁺-specific glucose dehydrogenase (GDH Ortho). The design principle discovered from Nox Ortho engineering and modeling is facilely translated onto six different enzymes to create NMN(H)-orthogonal biocatalysts with a consistent ~10³-10⁶-fold cofactor specificity switch from NAD(P)⁺ to NMN⁺. We assemble these enzymes to produce stereo-pure 2,3-butanediol in cell-free systems and in Escherichia coli, enabled by NMN(H)'s distinct redox ratio firmly set by its designated driving forces, decoupled from both NAD(H) and NADP(H).