Atypical Bacilliredoxin AbxC Plays a Role in Responding to Oxidative Stress in Radiation-Resistant Bacterium Deinococcus radiodurans.

Soyoung Jeong,Yong-Sun Bahn,Laurence Blanchard,Sangyong Lim,Arjan De Groot,Min-Kyu Kim,Jong-Hyun Jung,Sangryeol Ryu

doi:10.3390/antiox10071148

Abstract

Deinococcus radiodurans is a robust bacterium with extraordinary resistance to ionizing radiation and reactive oxygen species (ROS). D. radiodurans produces an antioxidant thiol compound called bacillithiol (BSH), but BSH-related enzymes have not been investigated. The D. radiodurans mutant lacking bshA (dr_1555), the first gene of the BSH biosynthetic pathway, was devoid of BSH and sensitive to hydrogen peroxide (H2O2) compared to the wild-type D. radiodurans strain. Three bacilliredoxin (Brx) proteins, BrxA, B, and C, have been identified in BSH-producing bacteria, such as Bacillus. D. radiodurans possesses DR_1832, a putative homolog of BrxC. However, because DR_1832 contains a novel signature motif (TCHKT) and a C-terminal region similar to the colicin-like immunity domain, we named it AbxC (atypical BrxC). The deletion of abxC also sensitized cells to H2O2. AbxC exhibited peroxidase activity in vitro, which was linked to nicotinamide adenine dinucleotide phosphate (NADPH) oxidation via the BSH disulfide reductase DR_2623 (DrBdr). AbxC proteins were present mainly as dimers after exposure to H2O2 in vitro, and the oxidized dimers were resolved to monomers by the reaction coupled with BSH as an electron donor, in which DrBdr transported reducing equivalents from NADPH to AbxC through BSH recycling. We identified 25 D. radiodurans proteins that potentially interact with AbxC using AbxC-affinity chromatography. Most of them are associated with cellular metabolisms, such as glycolysis and amino acid biosynthesis, and stress response. Interestingly, AbxC could bind to the proposed peroxide-sensing transcription regulator, DrOxyR. These results suggest that AbxC may be involved in the H2O2 signaling mechanism mediated by DrOxyR.

Highlights

We deleted the bshA gene in D. radiodurans to construct a BSH-deficient strain (∆bshA). ∆bshA did not show any alteration in growth in comparison to the wild-type D. radiodurans strain (WT)
When cells were labeled with monochlorobimane, BSH formed a complex with mBCl to generate the monobromobimane derivative of BSH [16]
∆abxC exposed to H2 O2 to wild-type strain (WT) levels (Figure 3C). These results suggest that the Trx-like protein AbxC contributes to D. radiodurans resistance to oxidative stress, and Cys36 plays a crucial role in the anti-oxidative function of AbxC

Summary

Introduction

Reactive oxygen species (ROS) are harmful byproducts of aerobic metabolism. ROS include superoxide anions (O2 − ), hydrogen peroxide (H2 O2 ), and hydroxyl radicals ( OH), which have inherent chemical reactivity [1]. Oxidative stress caused by excess ROS generation leads to damage to cellular components, including lipids, proteins, and DNA [2]. To cope with the adverse effects of ROS, bacteria have evolved elaborate antioxidant systems [2]. These include ROS scavenging enzymes, such as catalase (CAT), superoxide dismutase (SOD), and alkyl hydroperoxide reductase (AhpCF), and redox-active enzymes such as thioredoxin (Trx) and glutaredoxin (Grx) [3,4].

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Results

Conclusion