Résumé
Several genomic analyses, high-throughput or targeted interaction studies including the purification of protein complexes indicated a physical and functional link between BolAs and monothiol glutaredoxins (Grxs) that is conserved both in prokaryotes and eukaryotes. In Saccharomyces cerevisiae, the transfer of an Fe-S cluster from a complex formed by Grx3/4 and Fra2, a BolA member, to Aft transcription factors was proposed to regulate their nuclear translocation1. In a recent work, using binary yeast-two hybrid and bimolecular fluorescence complementation in Arabidopsis protoplasts, we confirmed that several Arabidopsis protein couples, used as plant representatives, also physically interact2. More interestingly, we determined that two BolA proteins, BolA2 and SufE1, contain a single conserved cysteine that is sensitive to oxidizing treatments. Oxidized forms of BolA2, either glutathionylated or containing an intermolecular disulfide bond, are efficiently reduced by monothiol Grxs, unraveling a possible redox-control of this protein by monothiol Grxs.From the structures of three A. thaliana BolAs, we highlighted the existence of two groups which differ primarily by the size of a loop referred to as the variable [H/C] loop. This loop contains one of the presumed Fe-S cluster ligands, a cysteine or a histidine for members BolA_C or BolA_H groups respectively. This has been confirmed by showing the presence of a Rieske-type [2Fe-2S] cluster for a holo-heterocomplex formed by BolA_H member and a monothiol Grx using 3D modeling, UV-visible absorption/CD, EPR, resonance Raman spectroscopies. On the other hand, NMR interaction experiments using apo-proteins indicated that a completely different heterodimer was formed, involving the nucleic acid binding site of BolA and the C-terminal tail of Grx.Altogether, the results indicated the formation of two types of complexes involving distinct regions in both partners. The possible biological importance of these complexes will be discussed considering the physiological functions previously assigned to BolA and to Grx-BolA or Grx-Grx complexes.[1] Poor et al (2014) Proc Natl Acad Sci USA. 2014, in press[2] Couturier et al (2014), Mol Plant, 7, 187.