A Novel Enzymatic System against Oxidative Stress in the Thermophilic Hydrogen-Oxidizing Bacterium Hydrogenobacter thermophilus

Yuya Sato,Masaharu Ishii,Hiroyuki Arai,Masafumi Kameya,Yasuo Igarashi,Shinya Fushinobu,Takayoshi Wakagi,Vasu D Appanna

doi:10.1371/journal.pone.0034825

Yuya Sato, Masaharu Ishii + Show 6 more

Open Access

https://doi.org/10.1371/journal.pone.0034825

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Journal: PloS one	Publication Date: Apr 2, 2012
Citations: 44	License type: CC BY 4.0

Affiliation: The University of Tokyo, Toyama Prefectural University

Abstract

Rubrerythrin (Rbr) is a non-heme iron protein composed of two distinctive domains and functions as a peroxidase in anaerobic organisms. A novel Rbr-like protein, ferriperoxin (Fpx), was identified in Hydrogenobacter thermophilus and was found not to possess the rubredoxin-like domain that is present in typical Rbrs. Although this protein is widely distributed among aerobic organisms, its function remains unknown. In this study, Fpx exhibited ferredoxin:NADPH oxidoreductase (FNR)-dependent peroxidase activity and reduced both hydrogen peroxide (H2O2) and organic hydroperoxide in the presence of NADPH and FNR as electron donors. The calculated Km and V max values of Fpx for organic hydroperoxides were comparable to that for H2O2, demonstrating a multiple reactivity of Fpx towards hydroperoxides. An fpx gene disruptant was unable to grow under aerobic conditions, whereas its growth profiles were comparable to those of the wild-type strain under anaerobic and microaerobic conditions, clearly indicating the indispensability of Fpx as an antioxidant of H. thermophilus in aerobic environments. Structural analysis suggested that domain-swapping occurs in Fpx, and this domain-swapped structure is well conserved among thermophiles, implying the importance of structural stability of domain-swapped conformation for thermal environments. In addition, Fpx was located on a deep branch of the phylogenetic tree of Rbr and Rbr-like proteins. This finding, taken together with the wide distribution of Fpx among Bacteria and Archaea, suggests that Fpx is an ancestral type of Rbr homolog that functions as an essential antioxidant and may be part of an ancestral peroxide-detoxification system.

Highlights

Molecular oxygen (O2) is the most abundant oxidant existing in the earth’s surface, an environment in which numerous organisms are distributed
Rbr has been reported to possess pyrophosphatase [7], ferroxidase [8], and superoxide dismutase (SOD) [2] activities, recent evidence suggests that it functions as a H2O2 reductase [6,9,10,11] to protect cells against oxidative stress
The cell-free extract (CFE) of the recombinant E. coli strain exhibited a yellow-greenish color, suggesting that Fpx was expressed as a holoprotein, as Fpx was predicted to possess a diiron domain that is known to have absorption in the visible range (

Summary

Introduction

Molecular oxygen (O2) is the most abundant oxidant existing in the earth’s surface, an environment in which numerous organisms are distributed. The utilization of O2 is associated with the risk of cellular damage from reactive oxygen species (ROS) that are derived from O2-related metabolism. ROS have high reactivity towards numerous cellular molecules, including nucleic acids and proteins, leading to irreversible damage and even cell death. To detoxify ROS, cells are equipped with various systems, such as superoxide reductase, catalase, hydrogen peroxide reductase, and organic peroxide reductase. Rbr has been reported to possess pyrophosphatase [7], ferroxidase [8], and superoxide dismutase (SOD) [2] activities, recent evidence suggests that it functions as a H2O2 reductase [6,9,10,11] to protect cells against oxidative stress

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