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The Mitochondrial Import Complex MIM Functions as Main Translocase for α-Helical Outer Membrane Proteins

Kim Nguyen Doan1, Alexander Grevel1, Christoph U Mårtensson1

  • 1Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.

Cell Reports
|April 30, 2020
PubMed

Insights

The mitochondrial import (MIM) complex inserts single-spanning proteins, previously poorly understood. This study reveals MIM

Area of Science:

  • Mitochondrial biology
  • Protein import and biogenesis
  • Cellular membrane dynamics

Background:

  • The mitochondrial outer membrane hosts integral proteins with α-helical or β-barrel structures.
  • While the import of β-barrel and multi-spanning α-helical proteins is understood, single-spanning protein biogenesis remains unclear.
  • Single-spanning proteins represent over half of integral outer membrane proteins.

Purpose of the Study:

  • To elucidate the biogenesis mechanism of single-spanning proteins in the mitochondrial outer membrane.
  • To investigate the role and mechanisms of the mitochondrial import (MIM) complex in protein insertion.

Main Methods:

  • Investigated the function of the yeast MIM complex in protein insertion.
  • Characterized the dynamic populations and interactions of the MIM complex.
  • Examined MIM complex interactions with the translocase of the outer membrane (TOM) and sorting and assembly machinery (SAM) complexes.

Main Results:

  • The MIM complex facilitates the insertion of proteins with N-terminal (signal-anchored) or C-terminal (tail-anchored) membrane anchors.
  • MIM exists in three dynamic populations, interacting with TOM for receptor-mediated import and independently for signal-anchored proteins.
  • MIM and SAM coupling is crucial for early assembly steps of TOM subunits.

Conclusions:

  • The MIM complex is a key player in the insertion of single-spanning proteins into the mitochondrial outer membrane.
  • MIM demonstrates versatility, acting as a major protein translocase for various protein types.
  • This study clarifies a significant gap in understanding mitochondrial protein biogenesis.
Keywords:
MIM complexSAM complexTOM complexmitochondriaouter membraneprotein assemblyprotein sortingprotein translocase

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