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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 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...
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...
Structure of Porins01:21

Structure of Porins

Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a  motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel precursors...
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

Updated: May 21, 2026

Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
09:01

Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria

Published on: January 7, 2022

Mitochondrial protein import: common principles and physiological networks.

Jan Dudek1, Peter Rehling, Martin van der Laan

  • 1Abteilung Biochemie II, Universität Göttingen, 37073 Göttingen, Germany.

Biochimica Et Biophysica Acta
|June 12, 2012
PubMed
Summary

Mitochondrial protein import relies on nuclear-encoded precursors guided by signals to translocases. These protein translocases cooperate and integrate into cellular networks like energy metabolism.

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Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
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Area of Science:

  • Cellular Biology
  • Biochemistry
  • Molecular Biology

Background:

  • Most mitochondrial proteins are synthesized in the cytosol as precursors.
  • These precursors require import into mitochondria via specific protein translocases.
  • Import signals dictate protein targeting and routing within mitochondria.

Purpose of the Study:

  • To review common principles of mitochondrial protein import.
  • To discuss mechanisms of protein integration into mitochondrial membranes.
  • To highlight the cooperation between mitochondrial protein translocases.

Main Methods:

  • Literature review of recent studies on mitochondrial protein import.
  • Analysis of protein targeting signals and translocase functions.
  • Discussion of the integration of protein import pathways with cellular processes.

Main Results:

  • Mitochondrial protein import involves precursor forms synthesized in the cytosol.
  • Specific import signals direct proteins to mitochondria and their destinations.
  • Mitochondrial protein translocases cooperate and are embedded in cellular networks.

Conclusions:

  • Mitochondrial protein import is a complex, coordinated process.
  • Protein translocase cooperation is essential for mitochondrial biogenesis.
  • Mitochondrial protein import pathways are interconnected with energy metabolism, signaling, and morphology.