Tailoring the Hinge Residue at the Substrate Access Tunnel Entrance Improves the Catalytic Performance of Industrialized Nitrile Hydratase Toward 3‐Cyanopyridine

Abstract Nicotinamide is a high‐value chemical that has been widely applied in various aspects of daily life. Nitrile hydratase (NHase) is capable of carrying out biotransformation of nitriles to amides and has shown great potential in the green synthesis of nicotinamide. The high‐molecular mass NHase (H‐NHase) from Rhodococcus rhodochrous J1 has been applied in the industrial‐scale production of acrylamide; however, its activity is not ideal towards aromatic 3‐cyanopyridines, resulting in its substrate preference towards aliphatic nitriles. In this study, a hinge residue at the entrance of the substrate access tunnel of H‐NHase was identified through substrate access tunnel calculations, site‐saturation mutagenesis, molecular docking and molecular dynamics simulations. The corresponding mutant βW48Y showed a 5.9‐fold higher specific activity towards 3‐cyanopyridine than that of its parental enzyme, with better thermostability, proving itself to be a competitive candidate for the industrial production of nicotinamide.