Transformation of the metabolically down-regulated mitochondrion of the mammalian bloodstream stage of Trypanosoma brucei to the ATP-producing mitochondrion of the insect procyclic stage is accompanied by the de novo synthesis of citric acid cycle enzymes and components of the respiratory chain. Because these metabolic pathways contain multiple iron-sulfur (FeS) proteins, their synthesis, including the formation of FeS clusters, is required. However, nothing is known about FeS cluster biogenesis in trypanosomes, organisms that are evolutionarily distant from yeast and humans. Here we demonstrate that two mitochondrial proteins, the cysteine desulfurase TbiscS and the metallochaperone TbiscU, are functionally conserved in trypanosomes and essential for this parasite. Knock-downs of TbiscS and TbiscU in the procyclic stage by means of RNA interference resulted in reduced activity of the marker FeS enzyme aconitase in both the mitochondrion and cytosol because of the lack of FeS clusters. Moreover, down-regulation of TbiscS and TbiscU affected the metabolism of procyclic T. brucei so that their mitochondria resembled the organelle of the bloodstream stage; mitochondrial ATP production was impaired, the activity of the respiratory chain protein complex ubiquinol-cytochrome-c reductase was reduced, and the production of pyruvate as an end product of glucose metabolism was enhanced. These results indicate that mitochondrial FeS cluster assembly is indispensable for completion of the T. brucei life cycle.

Multimodal imaging-therapeutic nanoprobe TiO(2)@RhdGd was prepared and successfully used for in vitro and in vivo cell tracking as well as for killing of cancer cells in vitro. TiO(2) nanoparticles were used as a core for phosphonic acid modified functionalities, responsible for contrast in MRI and optical imaging. The probe shows high (1)H relaxivity and relaxivity density values. Presence of fluorescent dye allows for visualization by means of fluorescence microscopy. The applicability of the probe was studied, using mesenchymal stem cells, cancer HeLa cells, and T-lymphocytes. The probe did not exhibit toxicity in any of these systems. Labeled cells were successfully visualized in vitro by means of fluorescence microscopy and MRI. Furthermore, it was shown that the probe TiO(2)@RhdGd can be changed into a cancer cell killer upon UV light irradiation. The above stated results represent a valuable proof of a principle showing applicability of the probe design for diagnosis and therapy.

Despite the significance of proteins containing iron‐sulfur cluster (Fe–S proteins), the processes of Fe–S cluster assembly and maturation of Fe–S proteins are poorly understood. However, several key proteins involved in the assembly have been identified, notably IscS, a cystein desulfurase, which provides sulfur for Fe–S cluster and IscU, a metallochaperone acting as a scaffold for cluster assembly. In this work, we studied the process of Fe–S cluster biosynthesis in Trypanosoma brucei by identifying the homologue of IscS in the T. brucei (TbIscS). To address the function of TbIscS, we inhibited its expression by means of RNA interference (RNAi). After RNAi induction, generation time of the TbIscS knock‐down cell line was significantly prolonged. All types of mitochondrial ATP production in the cells were severely affected. Analysis of glucose metabolism end products determined pyruvate as major excreted metabolite of the induced cells, while the uninduced cells produced only small amount of this glycolytic end product. These data demonstrate that mitochondrial metabolism is impaired in cells with TbIscS knocked down. To test whether the observed phenomena were results of Fe–S cluster assembly disruption, we examined the Fe–S cluster‐dependent activity of aconitase. This enzyme is localized in its active form in mitochondrion as well as in cytosol of T. brucei. After RNAi induction we observed the reduction of aconitase activity in both compartments (approx. 70% reduction in cytosol, approx. 30% in mitochondria). Western blots together with the EPR analysis showed that the reduction in cytosolic activity was due to impaired Fe–S cluster formation, while decrease in aconitase activity in mitochondria corresponded to the reduced level of the protein.