The Crystal structure of human GLRX5: iron sulphur cluster coordination, tetrameric assembly and monomer activity
Résumé
Human glutaredoxin 5 (GLRX5) is an evolutionarily conserved thiol-disulfide oxidoreductase that has a direct role in the maintenance of normal cytosolic and mitochondrial iron homeostasis and its expression affects haem biosynthesis and erythropoiesis. We have crystallised the human GLRX5 bound to two [2Fe2S] clusters and four glutathione (GSH) molecules. The crystal structure revealed a tetrameric organisation with the [2Fe2S] clusters buried in the interior and shielded from the solvent by the conserved β1-α2 loop, Phe69 and the GSH molecules. Each [2Fe2S] cluster is ligated by the N-terminal active site cysteine (Cys67) thiols contributed by two protomers and two cysteine thiols from two GSH. The two subunits coordinating the cluster are in a more extended conformation compared to FeS-bound human GLRX2 and the intersubunit interactions are more extensive and involve conserved residues among monothiol GLRXs. Gelfiltration chromatography and analytical ultracentrifugation supported a tetrameric organisation of holo GLRX5 while the apo protein is monomeric. Mass spectrometry analyses revealed glutathionylation of the cysteines in the absence of the [2Fe2S] cluster, which would protect them from further oxidation and possibly facilitate cluster transfer/acceptance. Apo GLRX5 reduced glutathione mixed disulfides with a rate 100 times slower than GLRX2 and was active as a glutathione-dependent electron donor for mammalian ribonucleotide reductase.
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