Understanding the Catalytic Determinant role of Diaphorase-Like Subunit in Formate Dehydrogenases via Redox Couples

Multi-subunit formate dehydrogenases (FDHs), which catalyze the interconversion of formate and carbon dioxide (CO₂), have drawn increasing attention for mitigating climate change and advancing environmental protection owing to their advantages of oxygen tolerance and easy heterogenous expression. However, differently sourced multi-subunit FDHs exhibit distinct catalytic biases, and the reasons remain unclear. On the basis of the exceptional observation of Rhodobacter aestuarii FDH favoring CO₂ reduction, this study unveiled an oxidation inhibition effect in exclusively NADH/NAD⁺-involved catalysis via kinetics analysis in terms of different redox couples. Substrate truncation positioned Fdhβ as the predominant subunit. Further studies based on structural and electrochemical insights interpreted that the slow desorption of NADH is the underlying determinant for the apparent catalytic bias. Knowledge-based rational design helped obtain a beneficial variant, RaFDH β E260Y, with a 10-fold increased catalytic activity in CO₂ reduction, highlighting its potential for CO₂ biotransformation and applications in low-carbon biomanufacturing. Eventually, bioinformatic analysis suggested that the diaphorase-like subunits and the catalysis regulation mechanism may widely exist in living organisms for modulating the redox balance of oxidoreductases, providing new insights into metabolism and catabolism.