Comparison of biotransformation mechanisms of 2, 4, 6-trinitrotoluene and its hydride-Meisenheimer metabolite by the old yellow enzyme family of flavoproteins

Abstract 2,4,6-trinitrotoluene (TNT) is a persistent pollutant; for removing it from environment, the biodegradation becomes an economical and environmentally friendly alternative. However, TNT is difficult to naturally mineralize due to the stability of benzene ring. Interestingly, the hydride metabolite (Hˉ-TNT) of TNT can produce dearomatized products by the biotransformation of old yellow enzyme (OYE) family, which is highly different with TNT. It is a promising strategy for the ring-opening degradation of TNT. Here, we explore the biotransformation difference of TNT and Hˉ-TNT by OYE family. The results show that the electron-withdrawing ability of nitro groups makes them obtain the majority of negative charges of Hˉ-TNT, which promotes the strong interaction between the substrate and key residues. It in turn promotes the formation of π-π stacking configuration between Hˉ-TNT and the flavin mononucleotide (FMN) cofactor, which is a preconditionofthe aromatic ring reduction. As a result, the aromatic ring reduction occupies an absolute advantage, while the nitro reduction is suppressed. The conclusions are in line with previous understanding and can explain experimental phenomena. This work can provide a valuable reference for the combined strategy of mineralizing TNT.