A Supercomplex Incorporating Both Electron Transport Chain and ATP Synthase

The mitochondrial oxidative phosphorylation system powering most aerobic organisms is typically depicted as two spatially segregated machineries(1): electron transport chain complexes I-IV (ETC CI-CIV) that generates proton motive force and adenosine triphosphate (ATP) synthase (complex V, CV) that consumes it(2,3). Using the kinetoplastid parasite Trypanosoma brucei in its procyclic form, we characterize a bona fide ETC-ATP synthase supercomplex that directly incorporates CII, CIV dimer and ATP synthase (CIICIV2CV) alongside conventional assemblies. Cryo-EM structure shows a clear organizing principle in which ATP synthase engages CIV2 via a non-canonical hetero-dimerization module of two subunit g paralogs, g’ and g’’, replacing the canonical g/g dimerization interface required for ATP synthase dimerization(4). The resulting ~2 MDa assembly forms an arc-shaped membrane region, which stabilizes shallow positive membrane curvature as indicated by atomistic simulations. Genetic disruption of g’/g’’ selectively destabilizes the supercomplex and triggers pronounced cristae remodeling from discoidal to elongated tubular form, accompanied by a reduced maximal polarization capacity and comparatively modest effects on steady-state ATP output. These findings establish a structurally defined ETC-ATP synthase supercomplex and suggest its primary role in architectural quality control, constraining ATP synthase supramolecular organization to safeguard mitochondrial integrity rather than simply enhancing chemiosmotic coupling.