Knockout of crtB or crtI gene blocks the carotenoid biosynthetic pathway in Deinococcus radiodurans R1 and influences it
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ORIGINAL PAPER
Knockout of crtB or crtI gene blocks the carotenoid biosynthetic pathway in Deinococcus radiodurans R1 and inXuences its resistance to oxidative DNA-damaging agents due to change of free radicals scavenging ability Lei Zhang · Qiao Yang · Xuesong Luo · Chengxiang Fang · Qiuju Zhang · Yali Tang
Received: 11 March 2007 / Revised: 7 May 2007 / Accepted: 14 May 2007 / Published online: 1 June 2007 © Springer-Verlag 2007
Abstract Deinococcus radiodurans R1, a red-pigmented strain of the extremely radioresistant genus Deinococcus, contains a major carotenoid namely deinoxanthin. The high resistance of this organism against the lethal actions of DNA-damaging agents including ionizing radiation and ultraviolet light (UV) has been widely reported. However, the possible antioxidant role of carotenoids in this strain has not been completely elucidated. In this study, we constructed two colorless mutants by knockout of crtB and crtI genes, respectively. Comparative analysis of the two colorless mutants and the wild type showed that the two colorless mutants were more sensitive to ionizing radiation, UV, and hydrogen peroxide, but not to mitomycin-C (MMC). With electron spin resonance (ESR) and spin trapping techniques, we observed that hydroxyl radical signals occurred in the suspensions of UV irradiated Deinococcus radiodurans cells and the intensity of signals was inXuenced by carotenoids levels. We further showed that the carotenoid extract from the wild type could obviously scavenge superoxide anions generated by the irradiated riboXavin/EDTA system. These results suggest that carotenoids in D. radiodurans R1 function as free radical scavengers to protect this organism against the deleterious eVects of oxidative DNAdamaging agents. Keywords Deinococcus radiodurans · Carotenoids · ESR · Free radical
Communicated by John Helmann. L. Zhang · Q. Yang · X. Luo · C. Fang (&) · Q. Zhang · Y. Tang College of Life Sciences, Wuhan University, Wuhan, 430072, People’s Republic of China e-mail: [email protected]
Abbreviations UV Ultraviolet light MMC Mitomycin-C ESR Electron spin resonance ROS Reactive oxygen species DMPO 5,5-Dimethyl-1-pyrroline-1-oxide
Introduction Reactive oxygen species (ROS) including superoxide anion (O¡ 2 ), hydrogen peroxide (H2O2), and hydroxyl radicals (·OH) are capable of damaging DNA, protein, and other cell components, generating a variety of oxidative damage (Ohshima et al. 1996; Shahmohammadi et al. 1998). The ROS scavenging system in a microbial cell consists of scavenging enzymes, including SOD, catalase and peroxidase, and non-enzymatic scavengers, such as metallothionein, glutathione and carotenoids (Tian et al. 2004). As a subfamily of the isoprenoids, carotenoids are responsible for many of the colors of animals, plants, and microorganisms and play important biological roles as accessory light-harvesting components of photosynthetic systems, photoprotecting antioxidants, and regulators of membrane Xuidity (Umeno et al. 2005). Carotenoids are considered to protect plants, animals,
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