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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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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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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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Porin Insertion in the Outer Mitochondrial Membrane01:12

Porin Insertion in the Outer Mitochondrial Membrane

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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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Energy to Drive Translocation01:37

Energy to Drive Translocation

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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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Related Experiment Video

Updated: Dec 26, 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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Studying protein import into mitochondria.

Chantal Priesnitz1, Nikolaus Pfanner2, Thomas Becker2

  • 1Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany; Faculty of Biology, University of Freiburg, Freiburg, Germany.

Methods in Cell Biology
|March 19, 2020
PubMed
Summary
This summary is machine-generated.

Mitochondria are vital for eukaryotic cell functions. In vitro protein import assays are essential for studying how proteins enter mitochondria and are sorted to their correct locations, aiding research on mitochondrial biogenesis.

Keywords:
Blue native electrophoresisMitochondriaProtein assemblyProtein importProtein sortingTIM23 complexTOM complex

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Area of Science:

  • Cell Biology
  • Mitochondrial Biology

Background:

  • Mitochondria perform essential cellular roles, including energy production and biosynthesis.
  • Mitochondrial function relies on the import and sorting of approximately 1000 proteins synthesized in the cytosol.
  • The translocase of the outer mitochondrial membrane (TOM) complex is the primary entry point for most mitochondrial proteins.

Purpose of the Study:

  • To highlight the significance of protein import into mitochondria.
  • To underscore the utility of in vitro protein import assays in understanding mitochondrial protein sorting.
  • To provide an overview of the complex protein translocation pathways within mitochondria.

Main Methods:

  • Utilizing in vitro import assays with isolated mitochondria.
  • Analyzing the kinetics of precursor protein transport.
  • Investigating precursor protein processing and assembly into functional complexes.

Main Results:

  • In vitro import assays have been pivotal in identifying protein-sorting routes into mitochondrial subcompartments.
  • These assays allow detailed studies of protein transport kinetics and precursor processing.
  • Established methods enable the examination of protein assembly into functional mitochondrial machineries.

Conclusions:

  • In vitro protein import assays are indispensable tools for mitochondrial research.
  • These assays facilitate a deeper understanding of mitochondrial protein biogenesis and function.
  • Continued use of these methods is crucial for advancing the field of mitochondrial biology.