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Related Concept Videos

Multi-pass Transmembrane Proteins and β-barrels01:09

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In multi-pass transmembrane proteins, the polypeptide chain crosses the membrane more than once. The transmembrane polypeptide chain either forms an α-helix or β-strand structure. α-Helix containing multi-pass transmembrane proteins are ubiquitous, whereas β-strand containing ones are mainly found in gram-negative bacteria, mitochondria, and chloroplasts.
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Porin Insertion in the Outer Mitochondrial Membrane01:12

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Porins are beta-barrel proteins translocated to the mitochondrial outer membrane through the TOM complex into the intermembrane space. Porin precursors bind TIM chaperones within the intermembrane space and are guided to the Sorting and Assembly Machinery complex or SAM complex on the outer mitochondrial membrane.
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The cell membrane, or plasma membrane, is an ever-changing landscape. It is described as a fluid mosaic where various macromolecules are embedded in the phospholipid bilayer. Among the macromolecules are proteins. The protein content varies across cell types. For example, mitochondrial inner membranes contain ~76% protein content, while myelin contains ~18% protein content. Individual cells contain many types of membrane proteins—red blood cells contain over 50—and different cell...
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The inner mitochondrial membrane is the primary site of ATP synthesis. The inner membrane domain that forms a smooth layer adjacent to the outer membrane is called the inner boundary membrane. This domain contains membrane transporters that drive metabolites in and out of the mitochondria.  In contrast, the inner membrane network that invaginates into the matrix space is called the cristae membrane. This domain accounts for principle mitochondrial function as it accommodates the protein...
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From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins
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Membrane protein insertion through a mitochondrial β-barrel gate.

Alexandra I C Höhr1,2, Caroline Lindau1,2, Christophe Wirth1

  • 1Institute of Biochemistry and Molecular Biology, Centre for Biochemistry and Molecular Cell Research (ZBMZ), Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany.

Science (New York, N.Y.)
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Summary

Mitochondrial Omp85 (Outer membrane protein 85) proteins insert precursor beta-barrel proteins into membranes. This study reveals precursors move through the Omp85 channel interior and exit via a lateral gate.

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Membrane Protein Biogenesis

Background:

  • Biogenesis of mitochondria, chloroplasts, and Gram-negative bacteria necessitates outer membrane insertion of beta-barrel proteins.
  • Homologous Omp85 proteins are crucial for inserting beta-barrel precursors into membranes.
  • The precise mechanism of beta-barrel precursor insertion via Omp85 remains unclear.

Purpose of the Study:

  • To elucidate the translocation pathway of beta-barrel precursors through the Omp85 channel.
  • To map the interaction between a precursor and the mitochondrial Omp85 homolog, Sam50, within its native membrane environment.

Main Methods:

  • In situ analysis of precursor-Omp85 interactions within the native membrane.
  • Mapping the transit of a beta-barrel precursor through the Sam50 channel.

Main Results:

  • The beta-barrel precursor is translocated into the interior of the Omp85 channel (Sam50).
  • Interaction occurs with an internal loop of Sam50, followed by insertion into the lateral gate via beta-signal exchange.
  • This suggests a mechanism involving transport through the Omp85 channel interior and release via a lateral gate.

Conclusions:

  • The Omp85-mediated insertion of beta-barrel proteins involves translocation into the channel interior.
  • Release into the lipid phase occurs through a lateral gate, potentially via beta-signal exchange.
  • This pathway may represent a fundamental mechanism for beta-barrel protein membrane insertion across different organisms.