Mitochondrial electron transport chain complexes are organized into supercomplexes responsible for carrying out cellular respiration. Here we present three architectures of mammalian (ovine) supercomplexes determined by cryo-electron microscopy. We identify two distinct arrangements of supercomplex CICIII 2 CIV (the respirasome) - a major 'tight' form and a minor 'loose' form (resolved at the resolution of 5.8 Å and 6.7 Å, respectively), which may represent different stages in supercomplex assembly or disassembly. We have also determined an architecture of supercomplex CICIII 2 at 7.8 Å resolution. All observed density can be attributed to the known 80 subunits of the individual complexes, including 132 transmembrane helices. The individual complexes form tight interactions that vary between the architectures, with complex IV subunit COX7a switching contact from complex III to complex I. The arrangement of active sites within the supercomplex may help control reactive oxygen species production. To our knowledge, these are the first complete architectures of the dominant, physiologically relevant state of the electron transport chain.
We thank the MRC LMB Cambridge for the use of the Titan Krios microscope. Data processing was performed using the IST high-performance computer cluster. J.A.L. holds a long-term fellowship from FEBS. K.F. is partially funded by a MRC UK PhD fellowship.
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Letts JA, Fiedorczuk K, Sazanov LA. The architecture of respiratory supercomplexes. Nature. 2016;537(7622):644-648. doi:10.1038/nature19774
Letts, J. A., Fiedorczuk, K., & Sazanov, L. A. (2016). The architecture of respiratory supercomplexes. Nature, 537(7622), 644–648. https://doi.org/10.1038/nature19774
Letts, James A, Karol Fiedorczuk, and Leonid A Sazanov. “The Architecture of Respiratory Supercomplexes.” Nature 537, no. 7622 (2016): 644–48. https://doi.org/10.1038/nature19774.
J. A. Letts, K. Fiedorczuk, and L. A. Sazanov, “The architecture of respiratory supercomplexes,” Nature, vol. 537, no. 7622, pp. 644–648, 2016.
Letts JA, Fiedorczuk K, Sazanov LA. 2016. The architecture of respiratory supercomplexes. Nature. 537(7622), 644–648.
Letts, James A., et al. “The Architecture of Respiratory Supercomplexes.” Nature, vol. 537, no. 7622, Nature Publishing Group, 2016, pp. 644–48, doi:10.1038/nature19774.