Seminar

Survival Kits of the World's Toughest Bacterium Deinococcus Radiodurans

조회수 : 237 등록일 : 2016.11.09 12:27

일시 : 2016.11.09 17:00
소속 : 한국원자력연구원
발표자 : 임상용
장소 : AS510
   Deinococcus radiodurans (D. radiodurans) is one of the most highly stress-resistant species reported. It can withstand extremely high doses of ionizing radiation (IR), long periods of desiccation, UV radiation and oxidizing agents. Although the mechanism underlying the resistance of D. radiodurans to IR has not been clearly elucidated, (i) various, effective DNA repair pathways, (ii) various enzymatic and non-enzymatic anti-oxidative systems, and (iii) some physical characteristics of nucleoids contribute to the extreme resistance of D. radiodurans. Extreme exposures to IR causes DNA single-strand breaks and double-strand breaks (DSBs), resulting in hundreds of short DNA fragments. DSBs repair in D. radiodurans is mainly achieved by extended synthesis dependent strand annealing (ESDSA). In addition, homologous recombination (HR), single strand annealing (SSA), and non-homologous end joining(NHEJ) participate in the DSB repair. Cellular exposure to IR leads to generation of reactive oxygen species (ROS) through radiolysis of water, such as superoxide radicals (O2·-), singlet oxygen (1O2), hydrogen peroxide (H2O2), and hydroxyl radicals (OH·), which damage cell membranes, proteins, and nucleic acids. D. radiodurans can remove reactive ROS through enzymatic and nonenzymatic systems. Since pyrroloquinoline-quinone (PQQ) was found to have ROS scavenging activity, other nonenzymatic antioxidants have also been identified in D. radiodurans, such as deinoxanthin, which is a unique ketocarotenoid exhibiting stronger ROS scavenging activity than other known carotenoid, and bacillithiol (BSH), which is an antioxidant thiol functionally analogous to glutathione. In addition, D. radiodurans is armed with ROS-scavenging Mn2+-metabolite complexes, which are known to facilitate its IR resistance through high levels of protein protection from oxidation. Regarding enzymatic systems, superoxide dismutase catalyzes the conversion of O2·- to H2O2, which is subsequently transformed into H2O by either catalases or peroxidases. D. radiodurans possesses four superoxide dismutases (DR0644, DR1279, DR1546, and DRA0202), three catalases (DR1998, DRA0146 and DRA0259), and two peroxidases (DRA0145 and DRA0301). Finally, a condensed nucleoid structure could favor error-free genome reassembly by limiting the diffusion of DNA fragments. Taken together, the radioresistance of D. radiodurans is the result of complex cell networks and further work is required to understand the combination of pathways that contributes to radioresistance at the molecular level.
 
 
 
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