Authors

Discussion

Thioredoxins are enzymes that sense changes in the cellular oxidation state and modulate specific pathways to maintain redox homeostasis. Mitochondrial thioredoxins (MTrxs) are involved in regulating cellular respiration in various organisms. Previous studies have shown that mitochondrial thioredoxins regulate essential mitochondrial functions and modulate ATP synthase subunits. Despite their essential roles and suggested involvement in mitochondrial redox regulation, the function of MTrxs in apicomplexans remains unknown. Here, we aimed to characterize, for the first time, a novel mitochondrial thioredoxin in Toxoplasma gondii to understand its role in parasite fitness and its involvement in the regulation of the oxidative phosphorylation pathway.

We identified a mitochondrial thioredoxin (MTrx1) and confirmed its mitochondrial localization. Furthermore, we demonstrated that its thioredoxin activity is essential for parasite growth and replication. We performed site-directed mutagenesis of a key cysteine residue critical for protein function and mapped its interactions through disulfide trapping. Depletion of MTrx1 resulted in reduced oxygen consumption leading to the investigation of how mitochondrial electron transport chain (mETC) functions were affected. We found that mETC activity and assembly were not significantly affected. However, ATP synthase assembly and ATP production were severely affected by MTrx1 knockdown, leading to defects in mitochondrial cristae formation. Overall, our work reveals, for the first time, an apicomplexan MTrx involved in the regulation of the mETC and ATP synthase function.