An essential role for an Fe-S cluster protein in the cytochrome c oxidase complex of Toxoplasma parasites.

The mitochondrial electron transport chain (ETC) of apicomplexan parasites differs considerably from the ETC of the animals that these parasites infect, and is the target of numerous anti-parasitic drugs. The cytochrome c oxidase complex (Complex IV) of the apicomplexan Toxoplasma gondii ETC is more than twice the mass and contains subunits not found in human Complex IV, including a 13 kDa protein termed TgApiCox13. TgApiCox13 is homologous to a human iron-sulfur (Fe-S) cluster-containing protein called the mitochondrial inner NEET protein (HsMiNT) which is not a component of Complex IV in humans. Here, we establish that TgApiCox13 is a critical component of Complex IV in T. gondii, required for complex activity and stability. Furthermore, we demonstrate that TgApiCox13, like its human homolog, binds two Fe-S clusters. We show that the Fe-S clusters of TgApiCox13 are critical for ETC function, having an essential role in mediating Complex IV integrity. Our study provides the first functional characterisation of an Fe-S protein in Complex IV.