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From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins
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Assembly of β-barrel proteins in the mitochondrial outer membrane

Alexandra I C Höhr1, Sebastian P Straub1, Bettina Warscheid2

  • 1Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany; Fakultät für Biologie, Universität Freiburg, 79104 Freiburg, Germany.

Biochimica Et Biophysica Acta
|October 12, 2014
PubMed

Insights

Mitochondria utilize the sorting and assembly machinery (SAM) complex to insert outer membrane proteins. This machinery, vital for eukaryotic cell function, shares similarities with bacterial systems.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Mitochondria originated from endosymbiotic Gram-negative bacteria, resulting in shared molecular machinery.
  • Outer mitochondrial and bacterial membranes feature β-barrel proteins essential for function.
  • Cytosolic precursor proteins are targeted to the mitochondrial intermembrane space for further processing.

Purpose of the Study:

  • To investigate the role of the mitochondrial sorting and assembly (SAM) machinery in β-barrel protein integration.
  • To elucidate the mechanisms by which the SAM complex facilitates protein insertion into the outer mitochondrial membrane.
  • To explore the connections between the SAM complex, other mitochondrial structures, and inter-organelle communication.

Main Methods:

  • Analysis of β-barrel protein topology and transport pathways.
  • Biochemical characterization of the SAM complex and its interactions.
  • Investigating the role of the β-signal in protein targeting and insertion.

Main Results:

  • The SAM complex, located in the outer mitochondrial membrane, is essential for folding and integrating β-barrel proteins.
  • A specific β-signal within the C-terminal β-strand of precursor proteins initiates their insertion.
  • The SAM complex mediates contact sites with the inner mitochondrial membrane via MICOS and interacts with ERMES, linking mitochondria and ER.

Conclusions:

  • The SAM complex is a key player in mitochondrial outer membrane biogenesis, mirroring bacterial BAM functions.
  • Understanding SAM complex function provides insights into the evolutionary relationship between mitochondria and bacteria.
  • SAM complex-mediated membrane contacts are crucial for mitochondrial structure and inter-organelle communication.
Keywords:
BacteriaBeta-barrelMitochondriaOuter membraneProtein assemblyProtein import

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