biostudies-literatureMacLean AEBLRD VANIAID NIH HHSWellcome Trust1424-1433https://www.ebi.ac.uk/biostudies/studies/S-EPMC12350165biostudies-literatureUnknown32(8)The apicomplexan mitochondrial electron transport chain is essential for parasite survival and displays a divergent subunit composition. Here we report cryo-electron microscopy structures of an apicomplexan III<sub>2</sub>-IV supercomplex and of the drug target complex III<sub>2</sub>. The supercomplex structure reveals how clade-specific subunits form an apicomplexan-conserved III<sub>2</sub>-IV interface with a unique, kinked architecture, suggesting that supercomplexes evolved independently in different eukaryotic lineages. A knockout resulting in supercomplex disassembly challenges the proposed role of III<sub>2</sub>-IV in electron transfer efficiency as suggested for mammals. Nevertheless, knockout analysis indicates that III<sub>2</sub>-IV is critical for parasite fitness. The complNature structural & molecular biologyStructure, assembly and inhibition of the Toxoplasma gondii respiratory chain supercomplex.PMC12350165I01 BX003312I01 BX004522IK6 BX004857R01 AI141412104111097945/B/11/ZR01 AI100569Liebman KMWinter RWSheiner LMeir AShikha SRiscoe MKPou SMuhleip ANilsen ADoggett JSFerreira Silva MGramelspacher MJMacLean AEfalseStructure, assembly and inhibition of the Toxoplasma gondii respiratory chain supercomplex.The apicomplexan mitochondrial electron transport chain is essential for parasite survival and displays a divergent subunit composition. Here we report cryo-electron microscopy structures of an apicomplexan III<sub>2</sub>-IV supercomplex and of the drug target complex III<sub>2</sub>. The supercomplex structure reveals how clade-specific subunits form an apicomplexan-conserved III<sub>2</sub>-IV interface with a unique, kinked architecture, suggesting that supercomplexes evolved independently in different eukaryotic lineages. A knockout resulting in supercomplex disassembly challenges the proposed role of III<sub>2</sub>-IV in electron transfer efficiency as suggested for mammals. Nevertheless, knockout analysis indicates that III<sub>2</sub>-IV is critical for parasite fitness. The compl2025-01-01T00:00:00Z2025 Aug2026-05-29T17:34:32.111Z2026-04-08T05:36:54.927ZS-EPMC123501654038967110.1038/s41594-025-01531-7