Nitroreductase Increases Menadione-Mediated Oxidative Stress in Aspergillus nidulans.
Appl Environ Microbiol
; 87(24): e0175821, 2021 11 24.
Article
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| MEDLINE
| ID: mdl-34613761
ABSTRACT
Nitroreductases (NTRs) catalyze the reduction of a wide range of nitro-compounds and quinones using NAD(P)H. Although the physiological functions of these enzymes remain obscure, a tentative function of resistance to reactive oxygen species (ROS) via the detoxification of menadione has been proposed. This suggestion is based primarily on the transcriptional or translational induction of an NTR response to menadione rather than on convincing experimental evidence. We investigated the performance of a fungal NTR from Aspergillus nidulans (AnNTR) exposed to menadione to address the question of whether NTR is really an ROS defense enzyme. We confirmed that AnNTR was transcriptionally induced by external menadione. We observed that menadione treatment generated cytotoxic levels of O2â¢-, which requires well-known antioxidant enzymes such as superoxide dismutase, catalase, and peroxiredoxin to protect A. nidulans against menadione-derived ROS stress. However, AnNTR was counterproductive for ROS defense, since knocking out AnNTR decreased the intracellular O2â¢- levels, resulting in fungal viability higher than that of the wild type. This observation implies that AnNTR may accelerate the generation of O2â¢- from menadione. Our in vitro experiments indicated that AnNTR uses NADPH to reduce menadione in a single-electron reaction, and the subsequent semiquinone-quinone redox cycling resulted in O2â¢- generation. We demonstrated that A. nidulans nitroreductase should be an ROS generator, but not an ROS scavenger, in the presence of menadione. Our results clarified the relationship between nitroreductase and menadione-derived ROS stress, which has long been ambiguous. IMPORTANCE Menadione is commonly used as an O2â¢- generator in studies of oxidative stress responses. However, the precise mechanism through which menadione mediates cellular O2â¢- generation, as well as the way in which cells respond, remains unclear. Elucidating these events will have important implications for the use of menadione in biological and medical studies. Our results show that the production of Aspergillus nidulans nitroreductase (AnNTR) was induced by menadione. However, the accumulated AnNTR did not protect cells but instead increased the cytotoxic effect of menadione through a single-electron reduction reaction. Our finding that nitroreductase is involved in the menadione-mediated O2â¢- generation pathway has clarified the relationship between nitroreductase and menadione-derived ROS stress, which has long been ambiguous.
Palabras clave
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Aspergillus nidulans
/
Nitrorreductasas
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Estrés Oxidativo
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Vitamina K 3
Idioma:
En
Revista:
Appl Environ Microbiol
Año:
2021
Tipo del documento:
Article