A myzozoan-specific protein is an essential membrane-anchoring component of the succinate dehydrogenase complex in Toxoplasma parasites.

Succinate dehydrogenase (SDH) is a protein complex that functions in the tricarboxylic acid cycle and the electron transport chain of mitochondria. In most eukaryotes, SDH is highly conserved and comprises the following four subunits: SdhA and SdhB form the catalytic core of the complex, while SdhC and SdhD anchor the complex in the membrane. Toxoplasma gondii is an apicomplexan parasite that infects one-third of humans worldwide. The genome of T. gondii encodes homologues of the catalytic subunits SdhA and SdhB, although the physiological role of the SDH complex in the parasite and the identity of the membrane-anchoring subunits are poorly understood. Here, we show that the SDH complex contributes to optimal proliferation and O2 consumption in the disease-causing tachyzoite stage of the T. gondii life cycle. We characterize a small membrane-bound subunit of the SDH complex called mitochondrial protein ookinete developmental defect (MPODD), which is conserved among myzozoans, a phylogenetic grouping that incorporates apicomplexan parasites and their closest free-living relatives. We demonstrate that TgMPODD is essential for SDH activity and plays a key role in attaching the TgSdhA and TgSdhB proteins to the membrane anchor of the complex. Our findings highlight a unique and important feature of mitochondrial energy metabolism in apicomplexan parasites and their relatives.

Harnessing cholesterol uptake of malaria parasites for therapeutic applications.

Parasites, such as the malaria parasite P. falciparum, are critically dependent on host nutrients. Interference with nutrient uptake can lead to parasite death and, therefore, serve as a successful treatment strategy. P. falciparum parasites cannot synthesise cholesterol, and instead source this lipid from the host. Here, we tested whether cholesterol uptake pathways could be 'hijacked' for optimal drug delivery to the intracellular parasite. We found that fluorescent cholesterol analogues were delivered from the extracellular environment to the intracellular parasite. We investigated the uptake and inhibitory effects of conjugate compounds, where proven antimalarial drugs (primaquine and artesunate) were attached to steroids that mimic the structure of cholesterol. These conjugated antimalarial drugs improved the inhibitory effects against multiple parasite lifecycle stages, multiple parasite species, and drug-resistant parasites, whilst also lowering the toxicity to human host cells. Steroids with introduced peroxides also displayed antimalarial activity. These results provide a proof-of-concept that cholesterol mimics can be developed as a drug delivery system against apicomplexan parasites with the potential to improve drug efficacy, increase therapeutic index, and defeat drug resistance.