Biomimetic mineralization of nitrile hydratase into a mesoporous cobalt-based metal-organic framework for efficient biocatalysis
Nitrile hydratases (NHases) have attracted considerable attention owing to their application in the synthesis of valuable amides under mild conditions. However, the poor stability of NHases still is one of the main drawbacks in their industrial application. Recently, mesoporous metal-organic frameworks (MOFs) have been explored as an attractive support material for immobilizing enzymes. Here, we encapsulated a recombinant cobalt-type NHase from Aurantimonas manganoxydans into the cobalt-based MOF ZIF-67 by a biomimetic mineralization strategy. The nano-catalyst NHase1229@ZIF-67 shows high catalytic activity for the hydration of 3-cyanopyridine to nicotinamide, and its specific activity reached 29.5 U/mg. The NHase1229@ZIF-67 nanoparticles show a significant improvement in the thermal stability of NHase1229. The optimum reaction temperature of NHase1229@ZIF-67 is at 50-55 °C, and it still remained 40% of the maximum activity at 70 °C. However, the free NHase1229 completely lost its catalytic activity at 70 °C. The half-lives of NHase1229@ZIF-67 at 30 and 40 °C were 102.0 h and 26.5 h, respectively. NHase1229@ZIF-67 nanoparticles exhibit an excellent cycling performance, and its catalytic efficiency did not significantly decrease in the initial 6 cycles using 0.9 M 3-cyanopyridine as the substrate. In a fed-batch reaction, NHase1229@ZIF-67 can efficiently hydrate 3-cyanopyridine to nicotinamide, and the space-time yield was calculated to be 110 g·L-1·h-1. Therefore, the cobalt-type NHase was immobilized in MOF ZIF-67, which is shown as a potential nanocatalyst for the large-scale industrial preparation of nicotinamide.