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Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
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A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...
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Nuclear encoded mitochondrial precursors are imported to the inner membrane in a multistep process involving two separate translocons, TIM22 and TIM23. TIM23 is a cation-selective pore that remains closed by the N terminal segment of the protein. Negative charges on the TIM23 act as a receptor for the incoming precursor, pulling the positively charged matrix-targeting sequence for peptide insertion and translocation.
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Mitochondria are double-membrane organelles of the eukaryotes involved in cellular metabolism, signaling, ATP synthesis, and programmed cell death.  Each of these processes requires specific proteins and enzymes that must be correctly sorted to the right mitochondrial subcompartment for the proper functioning of the organelle.
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A Model Membrane Platform for Reconstituting Mitochondrial Membrane Dynamics
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The ER membrane complex (EMC) can functionally replace the Oxa1 insertase in mitochondria.

Büsra Güngör1, Tamara Flohr1, Sriram G Garg2

  • 1Cell Biology, University of Kaiserslautern, Kaiserslautern, Germany.

Plos Biology
|March 1, 2022
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Summary
This summary is machine-generated.

Endoplasmic reticulum (ER) membrane protein insertion complexes, guided entry of tail anchor proteins (GET) and ER membrane complex (EMC), show evolutionary links to bacterial and mitochondrial machinery. Yeast mitochondria could be functionally complemented by ER proteins, suggesting conserved membrane insertion mechanisms.

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Two key protein complexes, the guided entry of tail anchor proteins (GET) and the ER membrane complex (EMC), facilitate membrane protein insertion in the endoplasmic reticulum (ER).
  • Structural similarities between ER insertion complex subunits and bacterial/mitochondrial YidC/Oxa1/Alb3 proteins suggest a shared evolutionary origin for membrane protein insertion machineries.

Purpose of the Study:

  • To investigate the functional conservation of ER membrane protein insertion machinery by testing if ER proteins can substitute for Oxa1 in yeast mitochondria.
  • To determine if mitochondria-targeted ER proteins can restore respiratory function and facilitate protein insertion in Oxa1 deletion mutants.

Main Methods:

  • Generation of yeast strains expressing mitochondria-targeted Get2-Get1 and Emc6-Emc3 fusion proteins.
  • Assessment of respiratory competence in Oxa1 deletion mutants complemented by ER protein fusions.
  • Analysis of the insertion and assembly of specific mitochondrial proteins (Cox2, inner membrane proteins, Atp9) in complemented strains.

Main Results:

  • The Emc6-Emc3 fusion protein successfully complemented the Oxa1 deletion mutant, restoring respiratory competence.
  • Emc6-Emc3 facilitated the insertion of both mitochondrially encoded (Cox2) and nuclear-encoded inner membrane proteins.
  • The Emc6-Emc3 fusion was unable to facilitate the assembly of the Atp9 ring structure.

Conclusions:

  • Protein insertion into the endoplasmic reticulum shares functional conservation with insertion mechanisms in bacteria and mitochondria.
  • Conserved topological principles likely govern membrane protein insertion across different cellular compartments and organisms.
  • The ER membrane complex (EMC) exhibits functional overlap with mitochondrial protein insertion machinery, highlighting evolutionary relatedness.