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Related Concept Videos

Protein Transport into the Inner Mitochondrial Membrane01:34

Protein Transport into the Inner Mitochondrial Membrane

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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.
Transport of mitochondrial precursors across the TIM23 channel is driven by...
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Mitochondrial Protein Sorting01:39

Mitochondrial Protein Sorting

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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.
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
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Mitochondrial Precursor Proteins01:39

Mitochondrial Precursor Proteins

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Mitochondrial precursors are partially unfolded or loosely folded polypeptide chains. Newly synthesized precursors are inhibited from spontaneously folding into their native conformation by the cytosolic chaperones, heat shock proteins 70 (Hsp70), and mitochondrial import stimulation factors (MSFs). Precursors bound to MSFs are guided to the TOM70-TOM37 receptors, while precursors bound to Hsp70  chaperones are targetted to TOM20-TOM22 receptor complexes.
Most of the mitochondrial...
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Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

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Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...
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Energy to Drive Translocation01:37

Energy to Drive Translocation

2.9K
Mitochondrial protein import is powered by two distinct energy sources: ATP hydrolysis and electrochemical potential across the inner membrane. Newly synthesized precursors are bound by cytosolic chaperones of the Hsp70 family, which guide them to the import receptors on the mitochondrial surface. Utilizing the energy of ATP hydrolysis, Hsp70 chaperones transfer these precursors to the TOM receptors on the mitochondrial outer membrane.
Generally, polypeptides are unfolded by two distinct...
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Protein Transport to the Inner Chloroplast Membrane01:18

Protein Transport to the Inner Chloroplast Membrane

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Proteins targeted to the inner chloroplast membrane, or plastid proteins, are transported by two general pathways: the stop-transfer and the re-insertion or post-import pathways. Most plastid proteins carry N-terminal transit sequences and internal import sequences targeting it to the specific chloroplast subcompartment. Proteins targeted by the stop-transfer pathway have internal hydrophobic sequences that inhibit their translocation into the stroma. As a result, these precursors are arrested...
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Related Experiment Video

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Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
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Mitochondrial protein import in trypanosomes: Expect the unexpected.

Anke Harsman1, André Schneider1

  • 1Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland.

Traffic (Copenhagen, Denmark)
|December 16, 2016
PubMed
Summary

Mitochondrial protein import evolved differently between yeast and Trypanosoma brucei, despite its crucial role in organelle function. Few protein import machinery subunits are conserved, revealing distinct evolutionary paths.

Keywords:
S. cerevisiaeT. bruceiTIM complexTOM complexevolutionary cell biologymitochondrial biogenesisprotein translocase

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Area of Science:

  • Cell Biology
  • Evolutionary Biology
  • Biochemistry

Background:

  • Mitochondria, crucial for cellular energy via oxidative phosphorylation, originated from endosymbiotic events.
  • The evolution of nuclear-controlled protein import systems defined mitochondria as organelles.
  • Over 95% of mitochondrial proteins are imported from the cytosol via membrane complexes.

Purpose of the Study:

  • To compare mitochondrial protein import mechanisms in yeast and Trypanosoma brucei.
  • To investigate the conservation and divergence of protein import machinery.
  • To discuss the evolutionary implications of observed differences.

Main Methods:

  • Comparative analysis of mitochondrial protein import systems.
  • Review of existing literature on yeast and Trypanosoma brucei mitochondrial protein import.
  • Phylogenetic comparison of import machinery components.

Main Results:

  • Significant differences in mitochondrial protein import machinery between yeast and T. brucei were identified.
  • Only a few subunits of the import machineries are conserved between the two species.
  • Yeast utilizes two distinct inner membrane translocases, while T. brucei employs a single translocase for multiple substrate types.

Conclusions:

  • Mitochondrial protein import pathways have undergone significant independent evolution.
  • The divergence highlights the adaptability of mitochondria in different organisms.
  • Comparative studies illuminate the evolutionary plasticity of essential cellular processes.