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Related Concept Videos

Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

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,...
Mitochondrial Protein Sorting01:39

Mitochondrial Protein Sorting

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

Protein Transport into the Inner Mitochondrial Membrane

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...
Mitochondrial Precursor Proteins01:39

Mitochondrial Precursor Proteins

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 precursors...
Energy to Drive Translocation01:37

Energy to Drive Translocation

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

Porin Insertion in the Outer Mitochondrial Membrane

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

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

Published on: January 7, 2022

Intercellular mitochondrial transfer and trans-mitophagy in response to protein import dysfunction.

Emily Glover1, Beth Wiseman2, Celyn Dugdale3

  • 1School of Biochemistry, University of Bristol , Bristol, UK.

The Journal of Cell Biology
|July 7, 2026
PubMed
Summary

Intercellular mitochondrial transfer via tunnelling nanotubes rescues cellular energy. This study reveals distinct trafficking pathways and degradation mechanisms for mitochondria, promoting cellular repair.

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In Vitro and In Vivo Detection of Mitophagy in Human Cells, C. Elegans, and Mice
08:40

In Vitro and In Vivo Detection of Mitophagy in Human Cells, C. Elegans, and Mice

Published on: November 22, 2017

Area of Science:

  • Cell Biology
  • Mitochondrial Biology
  • Organelle Homeostasis

Background:

  • Mitochondrial protein import is crucial for cellular energy and homeostasis, especially in high-demand cells like neurons.
  • Import failure disrupts cellular energy supplies, leading to cellular damage.
  • Previous work showed intercellular mitochondrial transfer (IMT) via tunnelling nanotubes (TNTs) rescues import failure, but the fate and mechanism were unclear.

Purpose of the Study:

  • To investigate the fate of transferred mitochondria during intercellular mitochondrial transfer (IMT).
  • To elucidate the mechanistic basis for rescue of mitochondrial import failure via IMT.
  • To differentiate the regulation and consequences of bidirectional mitochondrial trafficking.

Main Methods:

  • Comparative analysis of mitochondrial trafficking between import-defective and import-competent cells.
  • Observation of mitochondrial fragmentation and degradation pathways.
  • Identification of novel structures involved in mitochondrial accumulation and degradation.

Main Results:

  • Import-defective mitochondria are fragmented and undergo lysosomal degradation.
  • Reactive oxygen species (ROS)-producing mitochondria are transferred from competent to failing cells.
  • Transferred mitochondria accumulate in previously uncharacterized "mitochondrial degradation bodies" (MDBs).

Conclusions:

  • Bidirectional mitochondrial trafficking via TNTs exhibits distinct regulatory and consequential pathways.
  • A novel noncanonical "trans-mitophagy" process involving MDBs may contribute to mitochondrial regeneration.
  • These findings suggest a cooperative mechanism of mitochondrial repair and functional rescue through intercellular exchange.