A Nitroreductase from Cedecea sulfonylureivorans: Identification, Characterization, and Biocatalytic Potential

Abstract

Flavin-dependent nitroreductases are versatile FMN-containing oxidoreductases that catalyze the two-electron reduction of nitroaromatic compounds. Herein, we report the identification, and biochemical characterization of an oxygen-insensitive nitroreductase from Cedecea sulfonylureivorans LAM2020 (Cs-NR). The phylogenetic analysis places Cs-NR within the NfsB-type nitroreductases of the Enterobacteriaceae family, sharing conserved FMN-binding motifs. The enzyme operates optimally at neutral pH and at moderate temperatures and remains active under aerobic conditions using NADPH as a preferred cofactor. The kinetics shows Cs-NR exhibits highest catalytic efficiency towards nitrobenzene compare to NfsB of E. coli K12. Accordingly, Cs-NR was found to reduce a broad range of substituted nitroarenes to the corresponding amines in moderate to good conversions across 24 examples, enabling the preparative-scale synthesis of aniline derivatives in 10 examples. In addition, Cs-NR displayed reductive activity toward quinones (5 examples) and activated alkenes (5 examples). Notably, the preferential reduction of the alkene bond over the nitro group in nitrostyrene derivatives demonstrates the chemoselective nature of Cs-NR. Docking studies using an AlphaFold-generated structure rationalize binding of FMN with Cs-NR. Collectively, Cs-NR represents a robust and versatile biocatalyst for sustainable reductive transformations.