Engineering of the thermophilic nitrile hydratase from Pseudonocardia thermophila JCM3095 for large-scale nicotinamide production based on sequence-activity relationships

The green biocatalyst nitrile hydratase (NHase) is able to bio-transform 3-cyanopyridine into nicotinamide. As the NHase reaction is exothermic, an enzyme with high activity and stability is needed for nicotinamide production. In this study, we used sequence analysis and site-directed mutagenesis to generate a mutant of thermophilic NHase from Pseudonocardia thermophila JCM3095 with substantially enhanced activity and developed a powerful process for nicotinamide bio-production. The specific activity of αF126Y/αF168Y mutant was successfully increased by 3.98-fold over that of the wild-type enzyme. The half-life of such mutant was longer than 2 h, which was comparable to its parent enzyme. The relative activity of the αF126Y/αF168Y mutant after treatment with 1 M 3-cyanopyridine and 2 M nicotinamide was 73.2% and 63.7%, respectively, showing minor loss of its original stability. Structural analysis demonstrated that hydrogen bonds at the active site and α-β subunit interface of the NHase contribute to the improved activity and the maintenance of stability. Escherichia coli transformant harboring the mutant NHase was used for nicotinamide bio-production, yielding a nicotinamide productivity of 251.1 g/(L·h), which is higher than the productivity obtained using other NHase-containing strains and transformants. The newly established variant is therefore a promising alternative for the industrial production of nicotinamides.