Atomic structures of respiratory complex III(2), complex IV, and supercomplex III(2)-IV from vascular plants

Mitochondrial complex III (CIII(2)) and complex IV (CIV), which can associate into a higher-order supercomplex (SC III(2)+IV), play key roles in respiration. However, structures of these plant complexes remain unknown. We present atomic models of CIII(2), CIV, and SC III(2)+IV from Vigna radiata determined by single-particle cryoEM. The structures reveal plant-specific differences in the MPP domain of CIII(2) and define the subunit composition of CIV. Conformational heterogeneity analysis of CIII(2) revealed long-range, coordinated movements across the complex, as well as the motion of CIII(2)’s iron-sulfur head domain. The CIV structure suggests that, in plants, proton translocation does not occur via the H channel. The supercomplex interface differs significantly from that in yeast and bacteria in its interacting subunits, angle of approach and limited interactions in the mitochondrial matrix. These structures challenge long-standing assumptions about the plant complexes and generate new mechanistic hypotheses.