Abstract
BolA proteins are defined as stress-responsive transcriptional regulators, but they also participate in iron metabolism. Although they can form [2Fe-2S]-containing complexes with monothiol glutaredoxins (Grx), structural details are lacking. Three Arabidopsis thaliana BolA structures were solved. They differ primarily by the size of a loop referred to as the variable [H/C] loop, which contains an important cysteine (BolA_C group) or histidine (BolA_H group) residue. From three-dimensional modeling and spectroscopic analyses of A. thaliana GrxS14-BolA1 holo-heterodimer (BolA_H), we provide evidence for the coordination of a Rieske-type [2Fe-2S] cluster. For BolA_C members, the cysteine could replace the histidine as a ligand. NMR interaction experiments using apoproteins indicate that a completely different heterodimer was formed involving the nucleic acid binding site of BolA and the C-terminal tail of Grx. The possible biological importance of these complexes is discussed considering the physiological functions previously assigned to BolA and to Grx-BolA or Grx-Grx complexes.
Highlights
BolA and glutaredoxin interact together in the iron metabolism
BolA proteins are defined as stress-responsive transcriptional regulators, but they participate in iron metabolism
From three-dimensional modeling and spectroscopic analyses of A. thaliana GrxS14-BolA1 holo-heterodimer (BolA_H), we provide evidence for the coordination of a Rieske-type [2Fe-2S] cluster
Summary
BolA and glutaredoxin interact together in the iron metabolism. Results: They form two types of heterodimers with different binding surfaces depending on the presence or absence of an iron-sulfur cluster. BolA proteins are defined as stress-responsive transcriptional regulators, but they participate in iron metabolism They can form [2Fe-2S]-containing complexes with monothiol glutaredoxins (Grx), structural details are lacking. It was surprising that a BolA, referred to as Fra (Fe repressor of activation-2), and cytosolic monothiol Grx3/4 contributed to the regulation of iron homeostasis by forming stable [2Fe-2S] cluster-bridged holo-heterodimers controlling the nuclear translocation of the Saccharomyces cerevisiae Aft1/Aft transcription factors in response to a mitochondrial signal [5,6,7]. It was reported that Grx-BolA couples from various sources could form apo-heterodimers [7, 9] This is consistent with the observation that an in vivo Grx3/4-Fra interaction is found both in iron-replete and iron-depleted yeast cells [5]. From a previously established classification, these AtBolAs can be separated into two groups that contain either a conserved histidine (AtBolA1, AtBolA4, and SufE1BolA; BolA_H group) or cysteine
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