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NO sensing by FNR: regulation of the Escherichia coli NO‐detoxifying flavohaemoglobin, Hmp
Author(s) -
CruzRamos Hugo,
Crack Jason,
Wu Guanghui,
Hughes Martin N.,
Scott Colin,
Thomson Andrew J.,
Green Jeffrey,
Poole Robert K.
Publication year - 2002
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/cdf339
Subject(s) - biology , escherichia coli , biochemistry , transcription (linguistics) , bacteria , promoter , enterobacteriaceae , nitric oxide , gene , gene expression , microbiology and biotechnology , genetics , philosophy , linguistics , endocrinology
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.