Identification of NAD(P)H Quinone Oxidoreductase Activity in Azoreductases from P. aeruginosa: Azoreductases and NAD(P)H Quinone Oxidoreductases Belong to the Same FMN-Dependent Superfamily of Enzymes

Abstract

Water soluble quinones are a group of cytotoxic anti-bacterial compounds that are secreted by many species of plants, invertebrates, fungi and bacteria. Studies in a number of species have shown the importance of quinones in response to pathogenic bacteria of the genus Pseudomonas. Two electron reduction is an important mechanism of quinone detoxification as it generates the less toxic quinol. In most organisms this reaction is carried out by a group of flavoenzymes known as NAD(P)H quinone oxidoreductases. Azoreductases have previously been separate from this group, however using azoreductases from Pseudomonas aeruginosa we show that they can rapidly reduce quinones. Azoreductases from the same organism are also shown to have distinct substrate specificity profiles allowing them to reduce a wide range of quinones. The azoreductase family is also shown to be more extensive than originally thought, due to the large sequence divergence amongst its members. As both NAD(P)H quinone oxidoreductases and azoreductases have related reaction mechanisms it is proposed that they form an enzyme superfamily. The ubiquitous and diverse nature of azoreductases alongside their broad substrate specificity, indicates they play a wide role in cellular survival under adverse conditions.

Azoreductase: a key player of xenobiotic metabolism

“…As reviewed by Ryan (2017) and Koppel et al (2017), there are very few NQOs characterized from human gut bacterial strains. Recently, Ryan et al (2014) identified the NAD(P)H quinone oxidoreductase activity in azoreductase from P. aeruginosa and demonstrated that the azoreductases and the NAD(P)H quinone oxidoreductases belong to the same FMN-dependent azoreductase superfamily.…”

“…1 Azoreduction mechanism of amaranth dye by azoreductase enzyme: The UV-Visible spectrum demonstrating the complete reduction of amaranth dye in 24 h of incubation with purified azoreductase. Blue spectrum was recorded at zero time and green was recorded at 24 h oxidoreductases from homo sapiens and human gut bacteria (Liu et al 2008;Ryan et al 2014). …”

Functional Annotation of a Presumed Nitronate Monoxygenase Reveals a New Class of NADH:Quinone Reductases

“…Convergent evolution of azoreductases and quinone reductases has been proposed based on similar reaction mechanisms involving the flavin-mediated reduction of an organic molecule with NAD(P)H and substrate scope (37,38). The lack of enzymatic activity with the azo dye methyl red indicates that PA1024 is not an azoreductase.…”

“…The lack of enzymatic activity with the azo dye methyl red indicates that PA1024 is not an azoreductase. Although there are several azoreductases from P. aeruginosa capable of reducing quinones (38), WrbA is the only other two-electron NAD(P)H: quinone reductase identified to date that does not possess azoreductase activity (39) beside PA1024.…”

Pseudomonas aeruginosa LysR PA4203 Regulator NmoR Acts as a Repressor of the PA4202 nmoA Gene, Encoding a Nitronate Monooxygenase

“…The PA1225 gene is monocistronic, but any direct binding of PA4203 to the upstream intergenic region was ruled out in this study, suggesting that the effect might be due to the overexpression of nmoA. In a recent publication, Ryan et al suggested that the PA1225 protein is a soluble quinone reductase involved in the detoxification of quinones by their reduction to quinols (43). Further work will be needed to investigate the function of this dehy-…”