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Updated: Nov 22, 2025
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Assessment of Submitochondrial Protein Localization in Budding Yeast Saccharomyces cerevisiae
Published on: July 19, 2021
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Mitochondrial sorting and assembly machinery operates by β-barrel switching.
Hironori Takeda1, Akihisa Tsutsumi2, Tomohiro Nishizawa3
1Faculty of Life Sciences, Kyoto Sangyo University, Kamigamo-motoyama, Kyoto, Japan.
Nature
|January 7, 2021
Summary
Mitochondrial sorting and assembly machinery (SAM) complex structures reveal how β-barrel proteins are inserted into the outer membrane. The study elucidates the dynamic mechanism of substrate protein transfer within the SAM complex.
Area of Science:
- Cell Biology
- Structural Biology
- Biochemistry
Background:
- Mitochondrial outer membrane proteins, known as β-barrel proteins, are essential for cellular communication.
- The mitochondrial sorting and assembly machinery (SAM) complex facilitates the insertion of these proteins.
Purpose of the Study:
- To determine the high-resolution structures of the yeast SAM complex in different functional states.
- To elucidate the mechanism by which the SAM complex inserts β-barrel proteins into the mitochondrial outer membrane.
Main Methods:
- Cryo-electron microscopy was employed to visualize the SAM complex at 2.8-3.2 Å resolution.
- Structural analysis of two distinct forms of the SAM complex, including variations in its protein composition.
Main Results:
- The dimeric SAM complex features Sam50 proteins with partially open lateral gates, stabilized by Sam35 and Sam37.
- The structure reveals how Sam37 recruits and traps the Mdm10 protein, a β-barrel protein, within its channel.
- A substrate-bound SAM complex model suggests Mdm10 and Sam50b act as placeholders for incoming β-barrel substrates.
Conclusions:
- A dynamic switching mechanism involving β-barrel subunits and substrates is proposed for protein insertion.
- This mechanism explains the folding and assembly of precursor proteins via the mitochondrial machinery.
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