Structural and spectroscopic insights into BolA-glutaredoxin complexes [Plant Biology]

July 10th, 2014 by Roret, T., Tsan, P., Couturier, J., Zhang, B., Johnson, M. K., Rouhier, N., Didierjean, C.

BolA proteins are defined as stress-responsive transcriptional regulators but they also participate to 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 3D 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 apo-proteins 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.