FNR is a direct oxygen sensor having a biphasic response curve.
FNR is a transcription regulator that controls the expression of target genes in response to anoxia. Anaerobiosis is accompanied by the acquisition of two [4Fe-4S]2+ clusters per FNR dimer and the ability to bind DNA site-specifically. Oxidation of the [4Fe-4S]2+ form of FNR by O2 produced a non-DNA-binding, transcriptionally inactive form which also contains an iron-sulfur cluster, recently identified by Mossbauer spectroscopy as a [2Fe-2S] cluster (Khoroshilova et al., 1997, PNAS. 94, 6078). Complete conversion needed at least 2.5-3.0 molecules of O2 per [4Fe-4S]2+ cluster. Using sub-stoicheiometric amounts of air-saturated buffer, stable equilibria were established in which the [4Fe-4S]2+ and [2Fe-2S]2+ forms co-exist and no EPR detectable free ferric ions were released. In contrast, a 20-fold molar excess K3Fe(CN)6 was required to oxidise the [4Fe-4S]2+ cluster and in this case, ferric ions were released. FNR is therefore a sensitive O2 sensor.
Jordan
P A
PA
Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences, University of East Anglia, Norwich, UK.
Thomson
A J
AJ
Ralph
E T
ET
Guest
J R
JR
Green
J
J
D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D015374:Biosensing Techniques; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D004578:Electron Spin Resonance Spectroscopy; D029968:Escherichia coli Proteins; D007501:Iron / Q000032:analysis; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D010100:Oxygen / Q000032:analysis; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D015204:Spectroscopy, Mossbauer; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D007506:Iron-Sulfur Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D004247:DNA; D007501:Iron; D010100:Oxygen