Binuclear [2Fe-2S] clusters in the Escherichia coli SoxR protein and role of the metal centers in transcription
Date of Original Version
SoxR protein of Escherichia coli is activated by superoxide-generating agents or nitric oxide as a powerful transcription activator of the soxS gene, whose product activates ~10 other promoters. SoxR contains non-heme iron essential for abortive initiation of transcription in vitro. Here we show that this metal dependence extends to full-length transcription in vitro. In the presence of E. coli σ70 RNA polymerase, iron-containing SoxR mediates open complex formation at the soxS promoter, as determined using footprinting with Cu-5-phenyl-1,10-phenanthroline. We investigated the nature of the SoxR iron center by chemical analyses and electron paramagnetic resonance spectroscopy. Dithionite-reduced Fe-SoxR exhibited an almost axial paramagnetic signature with g values of 2.01 and 1.93 observable up to 100 K. These features, together with quantitation of spin, iron, and S2-, and hydrodynamic evidence that SoxR is a homodimer in solution, indicate that (SoxR)2 contains two [2Fe-2S] clusters. Treatment of Fe-SoxR with high concentrations of dithiothreitol caused subtle changes in the visible absorption spectrum and blocked transcriptional activity without generating reduced [2Fe-2S] centers, hut was also associated with the loss of iron from the protein. However, lowering the thiol concentration by dilution allowed spontaneous regeneration of active Fe-SoxR.
Publication Title, e.g., Journal
Journal of Biological Chemistry
Hidalgo, E., J. M. Bollinger, T. M. Bradley, C. T. Walsh, and B. Demple. "Binuclear [2Fe-2S] clusters in the Escherichia coli SoxR protein and role of the metal centers in transcription." Journal of Biological Chemistry 270, 36 (1995). doi: 10.1074/jbc.270.36.20908.