Alleviating the trade-off by site-guided function switch of nitrilase to nitrile hydratase

•The trade-off between hydration activity and specific activity was found and alleviated in Mut0 of NIT6803.•Three key residues Q192, I201 and G101 were identified by computational prediction approach and multiple sequence alignments.•The triple mutant G101K/Q192H/I201M, successfully recovered the relative activity (82.6%) and enhanced the amide ratio of hydration activity (98.5%).•It expanded the toolbox of nitrilase-catalysed promiscuity for amide formation.