Monothiol Glutaredoxin-1 Is an Essential Iron-Sulfur Protein in the Mitochondrion of African Trypanosomes

African trypanosomes encode three monothiol glutaredoxins (1-C-Grx). 1-C-Grx1 occurs exclusively in the mitochondrion, and 1-C-Grx2 and -3 are predicted to be mitochondrial and cytosolic proteins, respectively. All three 1-C-Grx are expressed in both the mammalian bloodstream and the insect procyclic form of Trypanosoma brucei, with the highest levels found in stationary phase and starving parasites. In the rudimentary mitochondrion of bloodstream cells, 1-C-Grx1 reaches concentrations above 200 microm/subunit. Recombinant T. brucei 1-C-Grx1 exists as a noncovalent homodimer, whereas 1-C-Grx2 and 1-C-Grx3 are monomeric proteins. In vitro, dimeric 1-C-Grx1 coordinated an H(2)O(2)-sensitive [2Fe-2S] cluster that required GSH as an additional ligand. Both bloodstream and procyclic trypanosomes were refractory to down-regulation of 1-C-Grx1 expression by RNA interference. In procyclic parasites, the 1-c-grx1 alleles could only be deleted if an ectopic copy of the gene was expressed. A 5-10-fold overexpression of 1-C-Grx1 in both parasite forms did not yield a growth phenotype under optimal culture conditions. However, exposure of these cells to the iron chelator deferoxamine or H(2)O(2), but not to iron or menadione, impaired cell growth. Treatment of wild-type bloodstream parasites with deferoxamine and H(2)O(2) caused a 2-fold down- and up-regulation of 1-C-Grx1, respectively. The results point to an essential role of the mitochondrial 1-C-Grx1 in the iron metabolism of these parasites.