Mitochondrial ADP/ATP Carrier 1 Is Important for the Growth of Tachyzoites.

Metabolism associated with energy production is highly compartmentalized in eukaryotic cells. During this process, transporters that move metabolites across organelle membranes play pivotal roles. The highly conserved ADP/ATP carrier (AAC) involved in ATP and ADP exchange between the mitochondria and cytoplasm is key to linking the metabolic activities in these 2 compartments. The ATP produced in mitochondria can be exchanged with cytoplasmic ADP by AAC, thus satisfying the energy needs in the cytoplasm. Toxoplasma gondii is an obligate intracellular parasite with a wide range of hosts. Previous studies have shown that mitochondrial metabolism helps to parasitize diverse host cells. Here, we identified 2 putative mitochondria ADP/ATP carriers in with significant sequence similarity to known AACs from other eukaryotes. We examined the ATP transport function of AACs by expressing them in Escherichia coli cells and found that only AAC1 had ATP transport activity. Moreover, knockdown of AAC1 caused severe growth defects of parasites and heterologous expression of mouse ANT2 in the AAC1 depletion mutant restored its growth, revealing its importance for parasite growth. These results verified that AAC1 functions as the mitochondrial ADP/ATP carrier in T. gondii and the functional studies demonstrated the importance of AAC1 for tachyzoites growth. T. gondii has an efficient and flexible energy metabolism system to meet different growth needs. ATP is an energy-carrying molecule and needs to be exchanged between organelles with the assistance of transporters. However, the function of AACs has yet to be characterized. Here, we identified 2 putative AACs of T. gondii and verified that only AAC1 had ATP transport activity with expression in the intact E. coli cells. Detailed analyses found that AAC1 is critical for the growth of tachyzoites and AAC2 is dispensable. Moreover, complementation with mouse ANT2 restored the growth speed of iAAC1, further suggesting AAC1 functions as a mitochondrial ADP/ATP carrier. Our research demonstrated the importance of AAC1 for tachyzoites growth.