1IDT

Nitroreductase (NTR) isolated from Escherichia coli catalyses the reduction of nitroaromatics, such as nitrofurazone and nitrofurantoin, to hydroxylamines and quinones, such as menadione, to quinols and has potential uses in chemotherapy and bioremediation. Unusually, it can use either NADPH or NADH as the reducing agent. The enzyme is oxygen-insensitive in that it does not transfers electrons to oxygen to produce superoxide. NTR is part of a family of FMN-containing oxidoreductases that have broadly similar substrate specificities. These enzymes are dimeric and contain two active sites, catalysing nitroaromatic reduction via a ping-pong bi bi mechanism. The substrate binds over the pyrimidine and central rings of the flavin. A portion of helix H6 can flex to accommodate the differently sized inhibitors suggesting a mechanism for accommodating varied substrates. This enzyme was first isolated from bacteria growing in a weapons storage dump, and can reduce trinitrotoluene.

Some nitro containing antibiotics depend on activation by bacterial NTR. The native enzyme shows that the principal structural changes occur in the FMN cofactor and indicate that the enzyme itself is a relatively rigid structure that primarily provides a rigid structural framework on which hydride transfer occurs. NTR is of interest in suicide gene therapy, where NTR is used as an activating enzyme for nitroaromatic prodrugs. The hydroxylamines produced can target proteins and DNA, causing strand cleavage in the latter. They can also be further activated to produce DNA cross-linking.