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Zhang, B, Crack, JC, Subramanian, S, Green, J, Thomson, AJ, Le Brun, NE and Johnson, MK (2012) Reversible cycling between cysteine persulfide-ligated [2Fe-2S] and cysteine-ligated [4Fe-4S] clusters in the FNR regulatory protein. Proc. Natl. Acad. Sci. U.S.A. 109:15734-9


Fumarate and nitrate reduction (FNR) regulatory proteins are O(2)-sensing bacterial transcription factors that control the switch between aerobic and anaerobic metabolism. Under anaerobic conditions [4Fe-4S](2+)-FNR exists as a DNA-binding homodimer. In response to elevated oxygen levels, the [4Fe-4S](2+) cluster undergoes a rapid conversion to a [2Fe-2S](2+) cluster, resulting in a dimer-to-monomer transition and loss of site-specific DNA binding. In this work, resonance Raman and UV-visible absorption/CD spectroscopies and MS were used to characterize the interconversion between [4Fe-4S](2+) and [2Fe-2S](2+) clusters in Escherichia coli FNR. Selective (34)S labeling of the bridging sulfides in the [4Fe-4S](2+) cluster-bound form of FNR facilitated identification of resonantly enhanced Cys(32)S-(34)S stretching modes in the resonance Raman spectrum of the O(2)-exposed [2Fe-2S](2+) cluster-bound form of FNR. This result indicates O(2)-induced oxidation and retention of bridging sulfides in the form of [2Fe-2S](2+) cluster-bound cysteine persulfides. MS also demonstrates that multiple cysteine persulfides are formed on O(2) exposure of [4Fe-4S](2+)-FNR. The [4Fe-4S](2+) cluster in FNR can also be regenerated from the cysteine persulfide-coordinated [2Fe-2S](2+) cluster by anaerobic incubation with DTT and Fe(2+) ion in the absence of exogenous sulfide. Resonance Raman data indicate that this type of cluster conversion involving sulfide oxidation is not unique to FNR, because it also occurs in O(2)-exposed forms of O(2)-sensitive [4Fe-4S] clusters in radical S-adenosylmethionine enzymes. The results provide fresh insight into the molecular mechanism of O(2) sensing by FNR and iron-sulfur cluster conversion reactions in general, and suggest unique mechanisms for the assembly or repair of biological [4Fe-4S] clusters.


PubMed PMC3465412 Online version:10.1073/pnas.1208787109


Cysteine/chemistry; Cysteine/metabolism; Escherichia coli Proteins/chemistry; Escherichia coli Proteins/metabolism; Ferrous Compounds/chemistry; Ferrous Compounds/metabolism; Iron-Sulfur Proteins/chemistry; Iron-Sulfur Proteins/metabolism; Models, Chemical; Oxygen/chemistry; Oxygen/metabolism; Spectrum Analysis



Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status


GO:1900489: positive regulation of [2Fe-2S] cluster assembly




Fig. 2. Resonance Raman spectra of the O2-induced [4Fe-4S]2+ to [2Fe-2S]2+ cluster conversion of FNR with natural abundance (black spectra) and 34S-labeled (red spectra) bridging sulfides. (A) [4Fe-4S]-FNR prepared by anaerobic reconstitution.

CACAO 10703


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