Metabolic engineering and transhydrogenase effects on NADPH availability in Escherichia coli

The synthesis of several industrially useful compounds are cofactor-dependent, requiring reducing equivalents like NADPH in enzymatic reactions leading up to the synthesis of high-value compounds like polymers, chiral alcohols, and antibiotics. However, NADPH is costly and has limited intracellular availability. This study focuses on the study of the effect of the two transhydrogenase enzymes of Escherichia coli, PntAB and UdhA (SthA) on reducing equivalents-dependent biosynthesis. The production of (S)-2-chloropropionate from 2-chloroacrylate is used as a model system for monitoring NADPH availability because 2-haloacrylate reductase, the enzyme catalyzing the one-step conversion to (S)-2-chloropropionate in the synthesis pathway, requires NADPH as a cofactor. Results suggest that the presence of UdhA increases product yield and NADPH availability while the presence of PntAB has the opposite effect. A maximum product yield of 1.4 mol product/mol glucose was achieved aerobically in a pnt-deletion strain with udhA overexpression, a 150% improvement over the wild-type control strain.