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Dr. Spiro's research is currently focused on responses to nitric oxide, a toxic free radical that is a by-product of normal metabolic processes in bacteria, as well as being a chemical defense synthesized by host phagocytic cells in response to infection by pathogenic microorganisms.
Nitric oxide (NO) is a water-soluble free-radical gas that is toxic in biological systems by virtue of its reactivity towards proteins, metal ions, lipids and DNA. Eukaryotic phagocytic cells exploit this toxicity by synthesizing NO as one of the arsenal of poisonous molecules that are used to kill invading pathogens. Successful intra-cellular pathogens (such as Salmonella and Mycobacterium species) are able to resist phagocyte killing mechanisms. There is increasing evidence that the ability to detoxify NO is required by some pathogens for survival inside host cells.
NO is also synthesized by Bacteria as an intermediate or by-product of normal respiratory processes. Specifically, nitrite can be used as an electron acceptor for anaerobic respiration by the denitrifying Bacteria, which reduce nitrite to NO, and also use NO as an electron acceptor, reducing it to nitrous oxide. The enteric Bacteria reduce nitrite to ammonia, but also catalyze the reduction of nitrite to NO, such that NO is made at a low concentration as a by-product of nitrite respiration. Escherichia coli has three enzymes that reduce or oxidize NO to less toxic compounds, and we speculate that one or more of these enzymes has a role in protecting the cell against the NO that is made endogenously from nitrite. The same enzymes may allow pathogens such as Salmonella to detoxify the NO made by host cells.
All three NO detoxification systems are up-regulated by exposure to nitrite or NO, and our major interest is to characterize the regulatory mechanisms involved, using E. coli as a model system. We study a transcriptional activator called NorR, which controls expression of the genes encoding a flavorubredoxin that reduces NO to nitrous oxide under anaerobic conditions. We have defined the mechanism of NO sensing by NorR and charaterized the cis-acting regulatory sequences required for transcriptional regulation. Future work will continue to probe structure-function relationships in the NorR protein, and to identify any additional genes that are regulated by NorR.
We recently discovered a transcriptional repressor, NsrR, that regulates expression of a flavohemoglobin, which oxidizes NO to nitrate. NsrR regulates at least three other genes, the products of which have poorly defined roles in mediating NO resistance. An important goal now is to study the biochemistry of NsrR, with a view to understanding the mechanism by which repression is relieved by NO. We have recently used chromatin immunoprecipitation and microarray analysis (ChIP-on-chip) to define NsrR binding sites across the entire E. coli genome. This study has revealed that there are many more targets for NsrR regulation than we previously suspected, most of which do not have obvious roles in NO detoxification. Future work will use genetic, molecular and physiological approaches to probe the roles of NsrR-regulated genes.
In a broader sense, the lab is interested in defining the enzymatic source(s) of NO during nitrite respiration. We are interested to identify the proteins that provide protection against endogenously generated NO, and to identify the major cellular targets for the low concentrations of NO that are made during nitrite respiration.
The Publications section lists any and all publications worked on. Research Explorer's search engine indexes data in this field for keyword searches. The category field is a user defined field where any number of categories can be created by the user to categorize publications. For example, publications can be categorized by the Journal that they appear in. Please click here for available slides.
Escherichia coli Cytochrome c Nitrite Reductase NrfA S Spiro, J Van Wonderen, DJ Richardson
McKethan, B.L. and Spiro S. (2013) Cooperative and allosterically controlled nucleotide binding regulates the DNA binding activity of NrdR. Molecular Microbiology. 90: 278-289.
Zeng, J. and Spiro, S. (2013) Finely-tuned regulation of the aromatic amine degradation pathway in Escherichia coli. Journal of Bacteriology. 195: 5141-5150.
Non-Heme Iron Sensors of Reactive Oxygen and Nitrogen Species. Spiro, Stephen; D'Autreaux, Benoit. Antioxidants & Redox Signaling Volume: 17 Issue: 9 Pages: 1264-1276 Published: NOV 2012.
Nitrous oxide production and consumption: regulation of gene expression by gas-sensitive transcription factors. Spiro, Stephen. Philosophical Transactions of the Royal Society B-Biological Sciences Volume: 367 Issue: 1593 Pages: 1213-1225 Published: MAY 5 2012.
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Professor David Richardson University of East Anglia, UK
Professor Jay Hinton Trinity College, Dublin
Graduate and post-doctoral advisor
Professor John Guest, FRS, University of Sheffield, UK
Thesis advisor to
Heather Sears, 1995 [co-mentored with David J. Richardson]
Andrew Hinsley, 1995
Josa Wehrfritz, 1995 [co-mentored with David J. Richardson]
Ya-Hsin Hsiao, 1996 [co-mentored with David J. Richardson]
Lisa Crossman, 1997 [co-mentored with David J. Richardson]
Debbie Flanagan, 1998 [co-mentored with David J. Richardson]
Mehmet Kilic, 1999 [co-mentored with Geoffrey R. Moore]
Lisa Gregory, 2000 [co-mentored with David J. Richardson]
Neil Shearer, 2000
Gareth Butland, 2000 [co-mentored with David J. Richardson and Nicholas J. Watmough]
Allison Lewin, 2000 [co-mentored with Geoffrey R. Moore]
Phil Doughty, 2001 [co-mentored with Geoffrey R. Moore]
Clare Taylor, 2001 [co-mentored with David J. Richardson]
Michael Hill, 2001 [co-mentored with David J. Richardson]
Kerrie Allen-O'Rourke, 2004
Yi-Ying Lee, 2005
Nicholas Tucker, 2005 NorR [co-mentored with Ray Dixon]
Paul Mills, 2006 [co-mentored with David J. Richardson and Jay C. Hinton]
Post-doctoral advisor to
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