Cryo-EM structure of the respiratory I + III2 supercomplex from Arabidopsis thaliana at 2 Å resolution

Protein complexes of the mitochondrial respiratory chain assemble into respiratory supercomplexes. Here we present the high-resolution electron cryo-microscopy structure of the Arabidopsis respiratory supercomplex consisting of complex I and a complex III dimer, with a total of 68 protein subunits and numerous bound cofactors. A complex I-ferredoxin, subunit B14.7 and P9, a newly defined subunit of plant complex I, mediate supercomplex formation. The component complexes stabilize one another, enabling new detailed insights into their structure. We describe (1) an interrupted aqueous passage for proton translocation in the membrane arm of complex I; (2) a new coenzyme A within the carbonic anhydrase module of plant complex I defining a second catalytic centre; and (3) the water structure at the proton exit pathway of complex III2 with a co-purified ubiquinone in the Q(O) site. We propose that the main role of the plant supercomplex is to stabilize its components in the membrane.

Automated summary

Protein complexes of the mitochondrial respiratory chain can assemble into supercomplexes. In this study, the structure of an Arabidopsis respiratory supercomplex composed of complex I and a complex III dimer was determined using high-resolution electron cryo-microscopy. The supercomplex contains 68 protein subunits and numerous bound cofactors. The stabilization of component complexes enables insights into their structure, including an interrupted aqueous passage in complex I, a new coenzyme A in the carbonic anhydrase module of complex I, and the water structure in the proton exit pathway of complex III2.