Mitochondrial sorting and assembly machinery operates by β-barrel switching

Hironori Takeda, Akihisa Tsutsumi, Tomohiro Nishizawa, Caroline Lindau, Jon V. Busto, Lena-Sophie Wenz, Lars Ellenrieder, Kenichiro Imai, Sebastian P. Straub, Waltraut Mossmann, Jian Qiu, Yu Yamamori, Kentaro Tomii, Junko Suzuki, Takeshi Murata, Satoshi Ogasawara, Osamu Nureki, Thomas Becker, Nikolaus Pfanner, Nils Wiedemann, Masahide Kikkawa and Toshiya Endo ()
Additional contact information
Hironori Takeda: Kyoto Sangyo University, Kamigamo-motoyama
Akihisa Tsutsumi: The University of Tokyo
Tomohiro Nishizawa: The University of Tokyo
Caroline Lindau: University of Freiburg
Jon V. Busto: University of Freiburg
Lena-Sophie Wenz: University of Freiburg
Lars Ellenrieder: University of Freiburg
Kenichiro Imai: National Institute of Advanced Industrial Science and Technology (AIST)
Sebastian P. Straub: University of Freiburg
Waltraut Mossmann: University of Freiburg
Jian Qiu: University of Freiburg
Yu Yamamori: National Institute of Advanced Industrial Science and Technology (AIST)
Kentaro Tomii: National Institute of Advanced Industrial Science and Technology (AIST)
Junko Suzuki: Kyoto Sangyo University, Kamigamo-motoyama
Takeshi Murata: Chiba University
Satoshi Ogasawara: Chiba University
Osamu Nureki: The University of Tokyo
Thomas Becker: University of Freiburg
Nikolaus Pfanner: University of Freiburg
Nils Wiedemann: University of Freiburg
Masahide Kikkawa: The University of Tokyo
Toshiya Endo: Kyoto Sangyo University, Kamigamo-motoyama

Nature, 2021, vol. 590, issue 7844, 163-169

Abstract: Abstract The mitochondrial outer membrane contains so-called β-barrel proteins, which allow communication between the cytosol and the mitochondrial interior1–3. Insertion of β-barrel proteins into the outer membrane is mediated by the multisubunit mitochondrial sorting and assembly machinery (SAM, also known as TOB)4–6. Here we use cryo-electron microscopy to determine the structures of two different forms of the yeast SAM complex at a resolution of 2.8–3.2 Å. The dimeric complex contains two copies of the β-barrel channel protein Sam50—Sam50a and Sam50b—with partially open lateral gates. The peripheral membrane proteins Sam35 and Sam37 cap the Sam50 channels from the cytosolic side, and are crucial for the structural and functional integrity of the dimeric complex. In the second complex, Sam50b is replaced by the β-barrel protein Mdm10. In cooperation with Sam50a, Sam37 recruits and traps Mdm10 by penetrating the interior of its laterally closed β-barrel from the cytosolic side. The substrate-loaded SAM complex contains one each of Sam50, Sam35 and Sam37, but neither Mdm10 nor a second Sam50, suggesting that Mdm10 and Sam50b function as placeholders for a β-barrel substrate released from Sam50a. Our proposed mechanism for dynamic switching of β-barrel subunits and substrate explains how entire precursor proteins can fold in association with the mitochondrial machinery for β-barrel assembly.

Date: 2021
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DOI: 10.1038/s41586-020-03113-7

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