Nitroreductases: A Biocatalytic Alternative to Produce Aromatic Amines

Nitroreductases are enzymes that reduce nitro compounds to corresponding nitroso, hydroxylamino, and amino compounds. In the past 20 years, they have gathered interest in several applications such as degradation of xenobiotic nitroaromatics, pharmaceutical production of amines, and activation of prodrugs in medical applications.

In previous studies, nitroreductases have shown to produce the hydroxylamine equivalent of the substrate. The instability and carcinogenicity of this product has been a barrier in using this enzyme. Also, the lack of a method to detect aromatic amines over hydroxylamines was a major barrier in improving the selectivity of nitroreductases

We show the development of a novel high-throughput colorimetric assay that can identify the aromatic amine. This assay is used to screen multiple libraries that consist of mutations in the active site. Variants that were identified to have improved production of amine were characterized and compared to the wild-type enzyme.

In addition, by studying nitroreductases from Salmonella typhimurium (NRSal), Enterobacter cloacae (EntNR) and Mycobacterium smegmatis (NfnB) we have found a Hammett correlation in the reduction rate of various substituted nitro aromatic compounds. This in turn helps us identify specific targets for large-scale synthesis.