Superoxide destroys the [2Fe-2S]2+ cluster of FNR from Escherichia coli.
The oxygen sensing ability of the transcription factor FNR depends on the presence of a [4Fe-4S]2+ cluster. In the presence of O2, conversion of the [4Fe-4S]2+ cluster to a [2Fe-2S]2+ cluster inactivates FNR, but the fate of the [2Fe-2S]2+ cluster in cells grown under aerobic conditions is unknown. The present study shows that the predominant form of FNR in aerobic cells is apo-FNR (cluster-less FNR) indicating that the [2Fe-2S]2+ cluster, like the [4Fe-4S]2+ cluster, is not stable under these conditions. By quantifying the amount of [2Fe-2S]2+ cluster in 2Fe-FNR in vitro in the presence of various reductants and oxidants (GSH, DTT, cysteine, O2, hydrogen peroxide, and superoxide), we found that superoxide, a byproduct of aerobic metabolism, significantly destabilized the [2Fe-2S]2+ cluster. Mössbauer spectroscopy was used to monitor the effects of superoxide on 2Fe-FNR in vivo; under cellular conditions that favored superoxide production, we observed the disappearance of the signal representative of the [2Fe-2S]2+ cluster. We conclude that the [2Fe-2S]2+ cluster of FNR is labile to superoxide both in vitro and in vivo. This lability may explain the absence of the [2Fe-2S]2+ cluster form of FNR under aerobic growth conditions.
Sutton
Victoria R
VR
Program in Cellular & Molecular Biology, University of Wisconsin, Madison, Wisconsin 53706, USA.
Stubna
Audria
A
Patschkowski
Thomas
T
Münck
Eckard
E
Beinert
Helmut
H
Kiley
Patricia J
PJ
D000332:Aerobiosis; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D012996:Solutions; D015204:Spectroscopy, Mossbauer; D013385:Succinate Dehydrogenase / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism; D013481:Superoxides / Q000737:chemistry*; D014157:Transcription Factors / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism
D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D007506:Iron-Sulfur Proteins; D009097:Multienzyme Complexes; D012996:Solutions; D014157:Transcription Factors; D013481:Superoxides; D013455:Sulfur; D007501:Iron; C033727:fumarate reductase complex; D013385:Succinate Dehydrogenase; D010100:Oxygen