MdaB and NfrA, Two Novel Reductases Important in the Survival and Persistence of the Major Enteropathogen Campylobacter jejuni

Abstract

The paralogues RrpA and RrpB which are members of MarR family of DNA binding proteins are important for the survival of the global bacterial foodborne pathogen Campylobacter jejuni under redox stress. We report that RrpA is a positive regulator of mdaB , encoding a flavin-dependent quinone reductase that contributes to the protection from redox stress mediated by structurally diverse quinones, whilst RrpB negatively regulates the expression of cj1555c (renamed nfrA for NADPH-flavin reductase A), encoding a flavin reductase. NfrA reduces riboflavin at a greater rate than its derivatives, suggesting exogenous free flavins are the natural substrate. MdaB and NfrA both prefer NADPH as an electron donor. Cysteine substitution and post-translational modification analyses indicated that RrpA and RrpB employ a cysteine-based redox switch. Complete genome sequence analyses revealed mdaB is frequently found in Campylobacter and related Helicobacter spp ., whilst nfrA is predominant in C. jejuni strains. Quinones and flavins are redox cycling agents secreted by a wide range of cell-types that can form damaging superoxide by one-electron reactions. We propose a model for stress adaptation where MdaB and NfrA facilitate a two-electron reduction mechanism to the less toxic hydroquinones, thus aiding survival and persistence of this major pathogen. Importance Changes in cellular redox potential results in alteration in the oxidation state of intracellular metabolites and enzymes, consequently, cells make adjustments that favor growth and survival. The work we present here answers some of the many questions that have remained elusive over the years of investigation into the enigmatic microaerophile bacterium, Campylobacter jejuni . We employed molecular approaches to understand the regulation mechanisms and functional analyses to reveal the roles of two novel quinone and flavin reductases, both serve as major pools of cellular redox-active molecules. This work extends our knowledge on bacterial redox sensing mechanisms and the significance of hemostasis.

Exploiting Violet-Blue Light to Kill Campylobacter jejuni : Analysis of Global Responses, Modeling of Transcription Factor Activities, and Identification of Protein Targets

“…The most highly upregulated gene at T2 is colored purple. Dashed arrows for RrpB indicate uncertainty about its regulation of hspR , perR , and katA due to a discrepancy between microarray data ( 44 , 45 ), used for the connectivity matrix in this study, and RNAseq studies ( 46 ).…”

“…Interestingly, there are two MarR-type oxidative stress regulators in C. jejuni ( 44 ), but TFInfer suggested that only RrpB (Cj1556) and not RrpA (Cj1546) showed a significant VB light response. It should be noted that our connectivity matrix used microarray data from Gundogdu et al ( 44 , 45 ) which showed that RrpB regulates katA , perR , and hspR expression, but this was not apparent in a recent RNAseq study ( 46 ), so the role of RrpB remains uncertain.…”

Polar localization of CheO under hypoxia promotes Campylobacter jejuni chemotactic behavior within host

“…Previous studies demonstrated that C. jejuni has evolved metabolic pathways and a complex branched electron transport chain to support microaerobic growth [13][14][15][16]. In addition, C. jejuni possesses a repertoire of oxidative stress defense enzymes to detoxify reactive oxygen species and also produce hemerythrins to protect essential metabolic enzymes during oxygen exposure [17][18][19]. Other factors beyond metabolism and respiration also contribute to microaerobic adaptation.…”