Bioengineered yeast tethered respiratory supercomplexes reveal mechanisms governing efficient substrate utilization

The mitochondrial respiratory chain (MRC) enzymatic complexes, essential for aerobic energy transduction in eukaryotic cells, are organized into evolutionarily conserved higher-order structures known as supercomplexes (SCs). The elucidation of the physiological relevance of respiratory SCs is essential for our understanding of mitochondrial function and cellular bioenergetics, yet it has been severely hampered by the limited availability of experimental models isolating SC formation as the sole variable. In the yeast Saccharomyces cerevisiae, where SCs are formed by the association of complexes III and IV into III2IV1 and III2IV2 configurations, compelling evidence suggests that SCs confer a competitive advantage by facilitating cytochrome c diffusion along the SC surface and enhancing respiratory rates. However, the significance of the proposed MRC plasticity and the role of distinct SC conformations in substrate utilization remain unresolved, leaving critical gaps in our understanding of mitochondrial bioenergetics and the adaptive evolution of energy transduction. To address these open questions, we engineered a yeast strain expressing a covalently linked III2IV2 SC, whose high-resolution structure is virtually identical to wild-type. Exclusive expression of this tethered SC supports robust overall respiratory activity but selectively affects mitochondrial respiration of cytosolically-generated NADH. This is attributable to the preferential interaction of distinct SC species with mitochondrial NADH dehydrogenases. We propose that in yeast mitochondria, substrate-driven formation of defined respirasome-like SC organizations contributes to the optimization of electron fluxes across the MRC and support metabolic plasticity.