ChrR, a Soluble Quinone Reductase of Pseudomonas putida That Defends against H2O2

Abstract

Most bacteria contain soluble quinone-reducing flavoenzymes. However, no biological benefit for this activity has previously been demonstrated. ChrR of Pseudomonas putida is one such enzyme that has also been characterized as a chromate reductase; yet we propose that it is the quinone-reducing activity of ChrR that has the greatest biological significance. ChrR reduces quinones by simultaneous two-electron transfer, avoiding formation of highly reactive semiquinone intermediates and producing quinols that promote tolerance of H 2 O 2 . Expression of chrR was induced by H 2 O 2 , and levels of chrR expression in overexpressing, wild type, and knock-out mutant strains correlated with the H 2 O 2 tolerance and scavenging ability of each strain. The chrR expression level also correlated with intracellular H 2 O 2 levels as measured by protein carbonylation assays and fluorescence-activated cell scanning analysis with the H 2 O 2 -responsive dye H 2 DCFDA. Thus, enhancing the activity of ChrR in a chromate-remediating bacterial strain may not only increase the rate of chromate transformation, it may also augment the capacity of these cells to withstand the unavoidable production of H 2 O 2 that accompanies chromate reduction.

The Escherichia coli Azoreductase AzoR Is Involved in Resistance to Thiol-Specific Stress Caused by Electrophilic Quinones

“…The amino acid sequence of AzoR was aligned with those of other proteins possessing azo and/or quinone reductase activity, including ChrR of Pseudomonas putida, WrbA of E. coli, NQO1 of Homo sapiens, Lot6p of Saccharomyces cerevisiae, YvaB of B. subtilis, and AZR of R. sphaeroides (19,34,38,40,43,50). The sequence length varied, and the overall sequence similarity was not obvious.…”

“…However, benzo-and naphthoquinones were found to be much better substrates than anthraquinones (36). ChrR of P. putida and WrbA of E. coli and Archaeoglobus fulgidus were reported to reduce benzo-and naphthoquinone compounds (19,34). Lot6p of S. cerevisiae can utilize 1,4-benzoquinone and 1,4-naphthoquinone, but not 1,4-anthraquinone, as substrate (40).…”

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

“…NAD(P)H:quinone oxidoreductases have been implicated in the detoxification of quinones within intracellular pools, thereby exerting an antioxidant protective role. This is due to the fact that upon a two-electron reduction of quinones to the hydroquinones, the highly reactive semiquinones are bypassed, which in turn lowers free radical formation and consequent lipid peroxidation, formation of protein adducts, and DNA modifications (51)(52)(53). This could be the case for PA1024.…”

Remediation of chromium contaminants using bacteria

“…Characterization of chromate reduction by a flavin reductase from E. coli revealed faster reduction when compared to chemical reduction by NADH and glutathione suggesting that unlike eukaryotes, enzymatic reduction is the dominant mechanism in bacterial cells (Puzon et al 2002). Chromate reductase encoding genes vary according to the microorganism and also occurs in He et al (2009) plasmids, few literatures are available describing the gene sequence (Barak et al 2006;Gonzalez et al 2005). A soluble Cr(VI) reductase purified from the cytoplasm of E. coli ATCC 33456 was a dimmer with a molecular mass of 84 kDa.…”