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Related Concept Videos

Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

3.0K
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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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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Mitochondrial Protein Sorting01:39

Mitochondrial Protein Sorting

4.2K
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...
4.2K
Protein Transport into the Inner Mitochondrial Membrane01:34

Protein Transport into the Inner Mitochondrial Membrane

3.6K
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...
3.6K
Energy to Drive Translocation01:37

Energy to Drive Translocation

2.0K
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...
2.0K
Porin Insertion in the Outer Mitochondrial Membrane01:12

Porin Insertion in the Outer Mitochondrial Membrane

2.8K
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.
Three models describe the assembly of porins by the SAM complex and their insertion into the outer membrane. Model 1 suggests that porins are assembled outside the SAM channel as the...
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Related Experiment Video

Updated: May 31, 2025

Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
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Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria

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Mitochondrial protein import stress.

Nikolaus Pfanner1,2,3, Fabian den Brave4, Thomas Becker5

  • 1Institute of Biochemistry and Molecular Biology, ZBMB, Faculty of Medicine, University of Freiburg, Freiburg, Germany. nikolaus.pfanner@biochemie.uni-freiburg.de.

Nature Cell Biology
|January 22, 2025
PubMed
Summary
This summary is machine-generated.

Cells respond to mitochondrial protein import stress by clearing clogged import sites and activating stress pathways. This maintains cellular proteostasis and viability by managing unfolded precursor proteins.

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Related Experiment Videos

Last Updated: May 31, 2025

Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
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Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria

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Area of Science:

  • Cell Biology
  • Mitochondrial Biology
  • Proteostasis

Background:

  • Mitochondria require extensive protein import from the cytosol.
  • Chaperones maintain precursor proteins in an unfolded state for import.
  • Import defects cause precursor accumulation, stressing cellular proteostasis.

Purpose of the Study:

  • To discuss cellular responses to mitochondrial protein import stress.
  • To highlight the role of the import machinery in sensing dysfunction.
  • To explain how stress responses maintain cell viability.

Main Methods:

  • Literature review and discussion of cellular pathways.
  • Analysis of chaperone and proteasomal roles in stress response.
  • Integration of mitochondrial stress into cellular proteostasis networks.

Main Results:

  • Mitochondrial import machinery acts as a sensor for dysfunction.
  • Cells regenerate clogged import sites and induce stress responses.
  • Chaperone production and proteasomal activity increase to manage precursors.

Conclusions:

  • Mitochondria are integral to cellular proteostasis and stress response networks.
  • Cellular responses to import stress ensure mitochondrial function and cell viability.
  • The import machinery plays a critical role in cellular stress detection and signaling.