Atomic structures of respiratory complex III2, complex IV and supercomplex III2-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, generate new mechanistic hypotheses and allow for the generation of more selective agricultural inhibitors.