Nitroreductase activity of ferredoxin reductase BphA4 from Dyella ginsengisoli LA-4 by catalytic and structural properties analysis

Ferredoxin reductase BphA4 was well known as a component of biphenyl dioxygenase. However, there was little information about whether it could utilize nonphysiological oxidants as electron acceptors. In the present study, we reported the novel nitroreductase activity of BphA4_LA-4. The homology model of ferredoxin reductase BphA4 from Dyella ginsengisoli LA-4 was constructed. According to the alignment of three-dimensional structures, it was supposed that BphA4_LA-4 could function as nitroreductase. Recombinant His-tagged BphA4_LA-4 was purified with a molecular mass of 49.6±1 kDa. Biochemical characterization of purified BphA4_LA-4 possessed the nitroreductase activity with the optimal temperature 50°C and pH 8.0. The substrate spectrum and kinetics indicated BphA4_LA-4 could reduce several nitroaromatics with different apparent K _m values: m-dinitrobenzene (560 μM), o-dinitrobenzene (1,060 μM), o-nitroaniline (1,570 μM), m-nitrobenzoic acid (1,300 μM) and m-nitrophenol (67 μM). The nitroreductase activity was further explained by docking studies, which was indicated that Arg 288 should play an important role in binding nitroaromatics. Moreover, there existed a good linear correlation between lnK _m and calculated binding energy.