Overexpression of a nitrile hydratase from Klebsiella oxytoca KCTC 1686 in Escherichia coli and its biochemical characterization

Functional Expression and Characterization of a Panel of Cobalt and Iron-Dependent Nitrile Hydratases

Nitrile hydratases (NHase) catalyze the hydration of nitriles to the corresponding amides. We report on the heterologous expression of various nitrile hydratases. Some of these enzymes have been investigated by others and us before, but sixteen target proteins represent novel sequences. Of 21 target sequences, 4 iron and 16 cobalt containing proteins were functionally expressed from Escherichia coli BL21 (DE3) Gold. Cell free extracts were used for activity profiling and basic characterization of the NHases using the typical NHase substrate methacrylonitrile. Co-type NHases are more tolerant to high pH than Fe-type NHases. A screening for activity on three structurally diverse nitriles was carried out. Two novel Co-dependent NHases from Afipia broomeae and Roseobacter sp. and a new Fe-type NHase from Gordonia hydrophobica were very well expressed and hydrated methacrylonitrile, pyrazine-carbonitrile, and 3-amino-3-(p-toluoyl)propanenitrile. The Co-dependent NHases from Caballeronia jiangsuensis and Microvirga lotononidis, as well as two Fe-dependent NHases from Pseudomonades, were—in addition—able to produce the amide from cinnamonitrile. Summarizing, seven so far uncharacterized NHases are described to be promising biocatalysts.

Recent Advances and Promises in Nitrile Hydratase: From Mechanism to Industrial Applications

Nitrile hydratase (NHase, EC 4.2.1.84) is one type of metalloenzyme participating in the biotransformation of nitriles into amides. Given its catalytic specificity in amide production and eco-friendliness, NHase has overwhelmed its chemical counterpart during the past few decades. However, unclear catalytic mechanism, low thermostablity, and narrow substrate specificity limit the further application of NHase. During the past few years, numerous studies on the theoretical and industrial aspects of NHase have advanced the development of this green catalyst. This review critically focuses on NHase research from recent years, including the natural distribution, gene types, posttranslational modifications, expression, proposed catalytic mechanism, biochemical properties, and potential applications of NHase. The developments of NHase described here are not only useful for further application of NHase, but also beneficial for the development of the fields of biocatalysis and biotransformation.

N-terminal engineering of overlapping genes in the nitrile hydratase gene cluster improved its activity

Nitrile hydratase which catalyzes the hydration of nitriles to the corresponding amides is operon-encoded. However, when heterologously expressed, genes in the same operon are usually not equally expressed, and the ratio needs to be fine-tuned. A gene cluster of three genes (corresponding to α-subunit, β-subunit and activator) encoding the nitrile hydratase was cloned from Aurantimonas manganoxydans ATCC BAA-1229 and expressed in Escherichia coli. However, difficulty was encountered in heterologous expression of the activator and the expression level of β-subunit was lower than that of α-subunit, which together resulted in low catalytic efficiency. To improve the expression of activator, a set of SKIK tags were fused to the N-terminus of the activator. To elevate the expression level of β-subunit, a silent mutation strategy was applied in the overlapping sequence with α-subunit around its translation initial region. Finally, the expression of β-subunit and activator were improved and the maximum activity of NHase1229 was doubled, reaching 160 U/mL towards 3-cyanopyridine. These results indicate that N-terminal engineering is an efficient strategy for optimizing the expression of multiple genes in operons.