Elucidating the function of the chloroplastic glutaredoxin S16 of Arabidopsis thaliana.
Résumé
Glutaredoxins (GRXs) are oxidoreductases involved in diverse cellular processes through their capacity to reduce glutathionylated proteins and/or to coordinate iron-sulfur (Fe-S) clusters. The plant-specific, plastidial GRXS16 is a bimodular protein formed by an N-terminal endonuclease domain fused to a regular GRX domain. Deciphering its physiological role by reverse genetics may have been hampered so far by the existence of other plastidial GRXs. Here, we have deciphered the biochemical properties of the recombinant protein. It has the ability to bind several types of Fe-S clusters, a [2Fe-2S] cluster in a dimer or a [4Fe-4S] cluster in a tetramer. Both can be transferred to acceptor proteins, consistently with a role in the maturation of plastidial Fe-S proteins. Besides, it catalyzes the oxidation but not reduction of a redox-sensitive GFP2 (roGFP2) at the expense of glutathione. Accordingly, GRXS16 reacts efficiently with oxidized glutathione, leading to the formation of an intramolecular disulfide between the cysteines 158 and 215 that is not reduced by glutathione but by the light-dependent plastidial thioredoxin system. As GRXS16 reduction is key to Fe-S cluster binding or to catalyzing protein glutathionylation/deglutathionylation, the formation of this disulfide may constitute a redox switch in response to the dark or to oxidizing conditions.