The O2 sensitivity of the transcription factor FNR is controlled by Ser24 modulating the kinetics of [4Fe-4S] to [2Fe-2S] conversion.


Jervis, AJ; Crack, JC; White, G; Artymiuk, PJ; Cheesman, MR; Thomson, AJ; Le Brun, NE; Green, J; (2009) The O2 sensitivity of the transcription factor FNR is controlled by Ser24 modulating the kinetics of [4Fe-4S] to [2Fe-2S] conversion. Proceedings of the National Academy of Sciences of the United States of America, 106 (12). pp. 4659-64. ISSN 0027-8424 DOI: https://doi.org/10.1073/pnas.0804943106

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Abstract

: Fumarate and nitrate reduction regulatory (FNR) proteins are bacterial transcription factors that coordinate the switch between aerobic and anaerobic metabolism. In the absence of O(2), FNR binds a [4Fe-4S](2+) cluster (ligated by Cys-20, 23, 29, 122) promoting the formation of a transcriptionally active dimer. In the presence of O(2), FNR is converted into a monomeric, non-DNA-binding form containing a [2Fe-2S](2+) cluster. The reaction of the [4Fe-4S](2+) cluster with O(2) has been shown to proceed via a 2-step process, an O(2)-dependent 1-electron oxidation to yield a [3Fe-4S](+) intermediate with release of 1 Fe(2+) ion, followed by spontaneous rearrangement to the [2Fe-2S](2+) form with release of 1 Fe(3+) and 2 S(2-) ions. Here, we show that replacement of Ser-24 by Arg, His, Phe, Trp, or Tyr enhances aerobic activity of FNR in vivo. The FNR-S24F protein incorporates a [4Fe-4S](2+) cluster with spectroscopic properties similar to those of FNR. However, the substitution enhances the stability of the [4Fe-4S](2+) cluster in the presence of O(2). Kinetic analysis shows that both steps 1 and 2 are slower for FNR-S24F than for FNR. A molecular model suggests that step 1 of the FNR-S24F iron-sulfur cluster reaction with O(2) is inhibited by shielding of the iron ligand Cys-23, suggesting that Cys-23 or the cluster iron bound to it is a primary site of O(2) interaction. These data lead to a simple model of the FNR switch with physiological implications for the ability of FNR proteins to operate over different ranges of in vivo O(2) concentrations.

Item Type: Article
Faculty and Department: Faculty of Infectious and Tropical Diseases > Dept of Pathogen Molecular Biology
PubMed ID: 19261852
Web of Science ID: 264522600018
URI: http://researchonline.lshtm.ac.uk/id/eprint/27932

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