Discovery of a new Fe-type nitrile hydratase efficiently hydrating aliphatic and aromatic nitriles by genome mining

Microbial nitrile hydratases (NHases) are important industrial catalysts to produce valuable amides. However, only some NHase genes have been reported and studied at the molecular level. In this study, we developed a genome mining method to discover Fe-type NHases from GenBank. The putative NHase gene from Pseudomonas putida F1 was cloned and functionally expressed in Escherichia coli BL21 (DE3) by assisting of a putative activator gene adjacent to β-subunit region. Three recombinant plasmids containing NHase gene or the activator gene were designed and constructed. Maximal enzyme activity was obtained when the structural and activator genes were transcribed as one unit in plasmid pCDFDuet-1 at 18 °C. However, the expressed product did not show any NHase activity when the downstream activator gene was ignored, and the product completely existed in insoluble inclusion body. The activator gene might be involved in protein folding of the α- and β-subunits of NHase. In addition, the Fe-type NHase exhibited broad substrate specificity. The enzyme can efficiently hydrate aromatic nitriles, such as 3-cyanopyridine, 4-cyanopyridine, and benzonitrile, asides from aliphatic nitriles preferentially. Therefore, the recombinant NHase shows potential applications in some amides preparation.