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Related Concept Videos

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...
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,...
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...
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...
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...
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: Jun 23, 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

Multiple pathways for mitochondrial protein traffic.

Toshiya Endo1, Koji Yamano

  • 1Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan. endo@biochem.chem.nagoya-u.ac.jp

Biological Chemistry
|May 21, 2009
PubMed
Summary
This summary is machine-generated.

Mitochondria import over a thousand proteins synthesized in the cytosol. Translocator complexes and chaperones mediate protein sorting to mitochondrial compartments via multiple pathways.

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Area of Science:

  • Mitochondrial biology
  • Cellular and molecular biology
  • Protein trafficking

Background:

  • Mitochondria are vital organelles with complex protein import needs.
  • Most mitochondrial proteins are synthesized in the cytosol and must be targeted.
  • Efficient protein import and sorting are crucial for mitochondrial function.

Purpose of the Study:

  • To summarize current knowledge on mitochondrial protein import pathways.
  • To highlight the roles of translocators and chaperones in protein trafficking.
  • To provide an overview of the expanding field of mitochondrial protein sorting.

Main Methods:

  • Literature review and synthesis of existing research.
  • Analysis of established and emerging pathways for mitochondrial protein import.
  • Discussion of the molecular machinery involved in protein translocation and sorting.

Main Results:

  • Mitochondria contain 1000-2000 proteins requiring import and sorting.
  • Proteins are sorted to four distinct mitochondrial compartments: outer membrane, intermembrane space, inner membrane, and matrix.
  • At least five major pathways facilitate mitochondrial protein trafficking.

Conclusions:

  • Mitochondrial protein import is a multi-step process involving numerous proteins.
  • Translocator complexes and chaperones are key mediators of protein import and sorting.
  • Understanding these pathways is essential for comprehending mitochondrial biogenesis and function.