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Structure of the mitochondrial import gate reveals distinct preprotein paths

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The translocase of the outer mitochondrial membrane (TOM) is the main entry gate for proteins1–4. Here we use cryo-electron microscopy to report the structure of the yeast TOM core complex5–9 at 3.8 Å resolution. The structure reveals the high-resolution architecture of the translocator consisting of two Tom40 β-barrel channels and α-helical transmembrane subunits, providing insight into critical features conserved in all eukaryotes1–3. Each Tom40 β-barrel is surrounded by small Tom subunits, and tethered by two Tom22 and one phospholipid. The N-terminal extension of Tom40 forms a helix inside the channel; mutational analysis reveals its dual role in early and late steps in biogenesis of intermembrane-space proteins in cooperation with Tom5. Each Tom40 channel possesses two precursor exit sites: Tom22, Tom40 and Tom7 guide presequence-containing preproteins to the exit in the midst of the dimer, whereas Tom5 and the Tom40 N-extension guide presequence-less preproteins to the exit at the dimer periphery.

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Author information

Correspondence to Toshiya Endo.

Supplementary information

Supplementary Figures

This file contains Supplementary Figures S1 (alignment of the N-terminus to β-strand 14 of Tom40 from various organisms) and S2 (the uncropped version of all the blots, gels and plates in this study)

Reporting Summary

Supplementary Tables

This file contains Supplementary Tables S1-S4

Video 1

HS-AFM observation of the purified TOM complex on a mica plate (200 nm × 200 nm).

Video 2

HS-AFM observation of the purified TOM complex scattered on a mica plate showing conversion of the trimer to the dimer (50 nm × 50 nm).

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