Highly efficient biosynthesis of isonicotinamide through a substrate access tunnel engineered nitrile hydratase from Carbonactinospora thermoautotrophicus

Abstract

Isonicotinamide has important roles and application prospects in pharmaceutical, medical, and materials sciences. The biosynthesis of isonicotinamide has great advantages over chemical methods, but the biosynthesis of isonicotinamide has been reported for three decades and has not been industrialized yet. In this study, a thermophilic NHase from Carbonactinospora thermoautotrophicus was selected and then its activity was substantially improved by a “toolbox” screening strategy. The specific activity of the βL48D mutant towards 4-cyanopyridine was 307.02 ± 3.50 U mg⁻¹, which was 13.9 times higher than that of the WT C.t NHase (22.01 ± 1.30 U mg⁻¹). The structural analysis demonstrated that introduction of Asp into the βLeu48 site resulted in a larger catalytic cavity and better substrate orientations. Finally, a recombinant strain E. coli BL21 of the βL48D mutant was cultured at high cell density in a 5 L fermenter for high-level isonicotinamide production, developing a powerful process for isonicotinamide bio-production. The yield of isonicotinamide reached 2.89 M (352 g L⁻¹), the substrate (4-cyanopyridine) was exhausted and the conversion was 100%. These results prove that C.t NHase is a promising competitor for future industrial production of biosynthetic isonicotinamide.