We seek to understand the impact that oxidative stress has upon organisms by addressing three overarching questions: How are reactive oxygen species formed in biological environments? What biomolecules do they damage? And how do cells defend themselves against them? We have employed E. coli as a model organism, in part because we have such a detailed understanding of its physiology and biochemistry, and in part because this facultative anaerobe can be genetically manipulated in the absence of oxygen. Our next set of specific aims addresses each of these three issues: 1. Are cytoplasmic enzymes shielded from H202 that is generated by periplasmic enzymes? Is intracellular formation of reactive oxygen species especially rapid inside aerated anaerobes? Are these species the primary factor in blocking their aerobic growth? Do antibiotics actually trigger H202 stress? 2. Does superoxide damage mononuclear iron enzymes ? Do oxidants inhibit ferrochelatase? What other targets of these oxidants can we discover through transcriptome analysis? 3. How completely can manganese-fed E. coli dispense with iron? How efficiently is manganese delivered to metalloenzymes? Do lactic-acid bacteria that routinely experience H202 stress employ manganese, rather than iron, in mononuclear non-redox enzymes? What about obligate aerobes, such as eukaryotes? These questions follow directly from the results of the current project. They are fundamental to our understanding of oxidative stress in contexts of medical interest, including the pathogenicity of obligate anaerobes, the effectiveness of antibiotic and antitumor treatments, and the mechanisms by which phagocytes suppress microbial infections.
Toxic oxygen species are believed to underpin many phenomena of medical importance, including spontaneous carcinogenesis, autoimmune disorders, the action of radiation and chemotherapies, and the cellular immune response. The proposed work will identify types of cell damage that might serve as biomarkers to confirm or refute the role of oxidative stress in these processes, and it may illuminate the mechanisms bv which some cells escape toxicity.
|Sobota, Jason M; Gu, Mianzhi; Imlay, James A (2014) Intracellular hydrogen peroxide and superoxide poison 3-deoxy-D-arabinoheptulosonate 7-phosphate synthase, the first committed enzyme in the aromatic biosynthetic pathway of Escherichia coli. J Bacteriol 196:1980-91|
|Imlay, James A (2014) The mismetallation of enzymes during oxidative stress. J Biol Chem 289:28121-8|
|Singh, Atul K; Shin, Jung-Ho; Lee, Kang-Lok et al. (2013) Comparative study of SoxR activation by redox-active compounds. Mol Microbiol 90:983-96|
|Ravindra Kumar, Sripriya; Imlay, James A (2013) How Escherichia coli tolerates profuse hydrogen peroxide formation by a catabolic pathway. J Bacteriol 195:4569-79|
|Gu, Mianzhi; Imlay, James A (2013) Superoxide poisons mononuclear iron enzymes by causing mismetallation. Mol Microbiol 89:123-34|
|Liu, Yuanyuan; Imlay, James A (2013) Cell death from antibiotics without the involvement of reactive oxygen species. Science 339:1210-3|
|Imlay, James A (2013) The molecular mechanisms and physiological consequences of oxidative stress: lessons from a model bacterium. Nat Rev Microbiol 11:443-54|
|Imlay, James A (2011) Redox pioneer: professor Irwin Fridovich. Antioxid Redox Signal 14:335-40|
|Sobota, Jason M; Imlay, James A (2011) Iron enzyme ribulose-5-phosphate 3-epimerase in Escherichia coli is rapidly damaged by hydrogen peroxide but can be protected by manganese. Proc Natl Acad Sci U S A 108:5402-7|
|Liu, Yuanyuan; Bauer, Sarah C; Imlay, James A (2011) The YaaA protein of the Escherichia coli OxyR regulon lessens hydrogen peroxide toxicity by diminishing the amount of intracellular unincorporated iron. J Bacteriol 193:2186-96|
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