title: Responses of Mn2+ speciation in Deinococcus radiodurans and Escherichia coli to γ-radiation by advanced paramagnetic resonance methods.
abstract: The remarkable ability of bacterium Deinococcus radiodurans to survive extreme doses of γ-rays (12,000 Gy), 20 times greater than Escherichia coli, is undiminished by loss of Mn-dependent superoxide dismutase (SodA). D. radiodurans radiation resistance is attributed to the accumulation of low-molecular-weight (LMW) "antioxidant" Mn(2+)-metabolite complexes that protect essential enzymes from oxidative damage. However, in vivo information about such complexes within D. radiodurans cells is lacking, and the idea that they can supplant reactive-oxygen-species (ROS)-scavenging enzymes remains controversial. In this report, measurements by advanced paramagnetic resonance techniques [electron-spin-echo (ESE)-EPR/electron nuclear double resonance/ESE envelope modulation (ESEEM)] reveal differential details of the in vivo Mn(2+) speciation in D. radiodurans and E. coli cells and their responses to 10 kGy γ-irradiation. The Mn(2+) of D. radiodurans exists predominantly as LMW complexes with nitrogenous metabolites and orthophosphate, with negligible EPR signal from Mn(2+) of SodA. Thus, the extreme radiation resistance of D. radiodurans cells cannot be attributed to SodA. Correspondingly, 10 kGy irradiation causes no change in D. radiodurans Mn(2+) speciation, despite the paucity of holo-SodA. In contrast, the EPR signal of E. coli is dominated by signals from low-symmetry enzyme sites such as that of SodA, with a minority pool of LMW Mn(2+) complexes that show negligible coordination by nitrogenous metabolites. Nonetheless, irradiation of E. coli majorly changes LMW Mn(2+) speciation, with extensive binding of nitrogenous ligands created by irradiation. We infer that E. coli is highly susceptible to radiation-induced ROS because it lacks an adequate supply of LMW Mn antioxidants.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Ajay
authors.initials: A
authors.lastname: Sharma
authors.forename: Elena K
authors.initials: EK
authors.lastname: Gaidamakova
authors.forename: Vera Y
authors.initials: VY
authors.lastname: Matrosova
authors.forename: Brian
authors.initials: B
authors.lastname: Bennett
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Daly
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hoffman
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D034301:Deinococcus / Q000378:metabolism* / Q000528:radiation effects; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D004926:Escherichia coli / Q000378:metabolism* / Q000528:radiation effects; D005720:Gamma Rays; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013053:Spectrophotometry; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: D000975:Antioxidants; D001426:Bacterial Proteins; D008024:Ligands; D017382:Reactive Oxygen Species; D008345:Manganese; C095500:SodA protein, Bacteria; D013482:Superoxide Dismutase
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