Creation of a formate: malate oxidoreductase by fusion of dehydrogenase enzymes with PEGylated cofactor swing arms

Enzymatic biocatalysis can be limited by the necessity of soluble cofactors. Here, we introduced PEGylated nicotinamide adenine dinucleotide (NAD(H)) swing arms to two covalently fused dehydrogenase enzymes to eliminate their nicotinamide cofactor requirements. A formate dehydrogenase and cytosolic malate dehydrogenase were connected via SpyCatcher-SpyTag fusions. Bifunctionalized polyethylene glycol chains tethered NAD(H) to the fusion protein. This produced a formate:malate oxidoreductase that exhibited cofactor-independent ping-pong kinetics with predictable Michaelis constants. Kinetic modeling was used to explore the effective cofactor concentrations available for electron transfer in the complexes. This approach could be used to create additional cofactor-independent transhydrogenase biocatalysts by swapping fused dehydrogenases.