NO sensing by FNR: regulation of the Escherichia coli NO-detoxifying flavohaemoglobin, Hmp.
Nitric oxide (NO) is a signalling and defence molecule of major importance in biology. The flavohaemoglobin Hmp of Escherichia coli is involved in protective responses to NO. Because hmp gene transcription is repressed by the O(2)-responsive regulator FNR, we investigated whether FNR also senses NO. The [4Fe-4S](2+) cluster of FNR is oxygen labile and controls protein dimerization and site-specific DNA binding. NO reacts anaerobically with the Fe-S cluster of purified FNR, generating spectral changes consistent with formation of a dinitrosyl-iron-cysteine complex. NO-inactivated FNR can be reconstituted, suggesting physiological relevance. FNR binds at an FNR box within the hmp promoter (P(hmp)). FNR samples inactivated by either O(2) or NO bind specifically to P(hmp), but with lower affinity. Dose-dependent up-regulation of P(hmp) in vivo by NO concentrations of pathophysiological relevance is abolished by fnr mutation, and NO also modulates expression from model FNR-regulated promoters. Thus, FNR can respond to not only O(2), but also NO, with major implications for global gene regulation in bacteria. We propose an NO-mediated mechanism of hmp regulation by which E.coli responds to NO challenge.
Cruz-Ramos
Hugo
H
The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield S10 2TN, UK.
Crack
Jason
J
Wu
Guanghui
G
Hughes
Martin N
MN
Scott
Colin
C
Thomson
Andrew J
AJ
Green
Jeffrey
J
Poole
Robert K
RK
D000693:Anaerobiosis; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D004093:Dihydropteridine Reductase; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics; D029968:Escherichia coli Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000502:physiology*; D006420:Hemeproteins / Q000096:biosynthesis* / Q000235:genetics; D007506:Iron-Sulfur Proteins / Q000502:physiology*; D009247:NADH, NADPH Oxidoreductases; D009569:Nitric Oxide / Q000494:pharmacology / Q000502:physiology*; D010100:Oxygen / Q000494:pharmacology; D012045:Regulatory Sequences, Nucleic Acid; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D006420:Hemeproteins; D007506:Iron-Sulfur Proteins; D009569:Nitric Oxide; D004093:Dihydropteridine Reductase; C076538:hmp protein, E coli; D009247:NADH, NADPH Oxidoreductases; D010100:Oxygen