Thiol-disulfide redox dependence of heme binding and heme ligand switching in nuclear hormone receptor rev-erb{beta}.
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Gupta N, Ragsdale SW
Thiol-disulfide redox dependence of heme binding and heme ligand switching in nuclear hormone receptor rev-erb{beta}.
J Biol Chem. 2011 Feb 11;286(6):4392-403. doi: 10.1074/jbc.M110.193466. Epub 2010 Dec 1.
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- 21123168 [ View in PubMed]
- Abstract
Rev-erbbeta is a heme-binding nuclear hormone receptor that represses a broad spectrum of target genes involved in regulating metabolism, the circadian cycle, and proinflammatory responses. Here, we demonstrate that a thiol-disulfide redox switch controls the interaction between heme and the ligand-binding domain of Rev-erbbeta. The reduced dithiol state of Rev-erbbeta binds heme 5-fold more tightly than the oxidized disulfide state. By means of site-directed mutagenesis and by UV-visible and EPR spectroscopy, we also show that the ferric heme of reduced (dithiol) Rev-erbbeta can undergo a redox-triggered switch from imidazole/thiol ligation (via His-568 and Cys-384, based on a prior crystal structure) to His/neutral residue ligation upon oxidation to the disulfide form. On the other hand, we find that change in the redox state of iron has no effect on heme binding to the ligand-binding domain of the protein. The low dissociation constant for the complex between Fe(3+)- or Fe(2+)-heme and the reduced dithiol state of the protein (K(d) = approximately 20 nM) is in the range of the intracellular free heme concentration. We also determined that the Fe(2+)-heme bound to the ligand-binding domain of Rev-erbbeta has high affinity for CO (K(d) = 60 nM), which replaces one of the internal ligands when bound. We suggest that this thiol-disulfide redox switch is one mechanism by which oxidative stress is linked to circadian and/or metabolic imbalance. Heme dissociation from Rev-erbbeta has been shown to derepress the expression of target genes in response to changes in intracellular redox conditions. We propose that oxidative stress leads to oxidation of cysteine(s), thus releasing heme from Rev-erbbeta and altering its transcriptional activity.