Structure and assembly of the mammalian mitochondrial supercomplex CIII2CIV

• Published in: Nature (London) 2021-10, Vol.598 (7880), p.364-367
• Main Authors: Vercellino, Irene, Sazanov, Leonid A.
• Format: Article
• Language: English
• Subjects: 101/1; 101/28; 631/443/319/333/1465; 631/535/1258/1259; 631/57/1464; 631/57/2272/2276; 82; 82/16; 82/83; Assembly; C-Terminus; Conformation; Electron transfer; Electron transport; Electron transport chain; Enzymes; Humanities and Social Sciences; Intermediates; Mammals; Metabolism; Mitochondria; Monomers; multidisciplinary; Science; Science (multidisciplinary); Yeast
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-021-03927-z

The enzymes of the mitochondrial electron transport chain are key players of cell metabolism. Despite being active when isolated, in vivo they associate into supercomplexes 1 , whose precise role is debated. Supercomplexes CIII 2 CIV 1-2 (refs. 2 , 3 ), CICIII 2 (ref. 4 ) and CICIII 2 CIV (respirasome) 5 – 10 exist in mammals, but in contrast to CICIII 2 and the respirasome, to date the only known eukaryotic structures of CIII 2 CIV 1-2 come from Saccharomyces cerevisiae 11 , 12 and plants 13 , which have different organization. Here we present the first, to our knowledge, structures of mammalian (mouse and ovine) CIII 2 CIV and its assembly intermediates, in different conformations. We describe the assembly of CIII 2 CIV from the CIII 2 precursor to the final CIII 2 CIV conformation, driven by the insertion of the N terminus of the assembly factor SCAF1 (ref. 14 ) deep into CIII 2 , while its C terminus is integrated into CIV. Our structures (which include CICIII 2 and the respirasome) also confirm that SCAF1 is exclusively required for the assembly of CIII 2 CIV and has no role in the assembly of the respirasome. We show that CIII 2 is asymmetric due to the presence of only one copy of subunit 9, which straddles both monomers and prevents the attachment of a second copy of SCAF1 to CIII 2 , explaining the presence of one copy of CIV in CIII 2 CIV in mammals. Finally, we show that CIII 2 and CIV gain catalytic advantage when assembled into the supercomplex and propose a role for CIII 2 CIV in fine tuning the efficiency of electron transfer in the electron transport chain. SCAF1 is solely required for supercomplex CIII 2 CIV assembly and is not involved in the formation of the respirasome (supercomplex CICIII 2 CIV)