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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...
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...
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...

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Related Experiment Video

Updated: Jul 7, 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

Protein import into isolated mitochondria.

Dejana Mokranjac1, Walter Neupert

  • 1Institut für Physiologische Chemie, Ludwig-Maximilians-Universität München, Germany.

Methods in Molecular Biology (Clifton, N.J.)
|March 5, 2008
PubMed
Summary
This summary is machine-generated.

Protein import into mitochondria is crucial for mitochondrial biogenesis. Researchers use in vitro import systems and genetic methods to identify key protein translocation machinery components.

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Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
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Isolation and Respiratory Measurements of Mitochondria from Arabidopsis thaliana
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Isolation and Respiratory Measurements of Mitochondria from Arabidopsis thaliana

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Mitochondria require numerous proteins for function, with most encoded by nuclear DNA.
  • These proteins are synthesized in the cytosol as precursors and imported into mitochondria.
  • Understanding this import process is vital for mitochondrial biogenesis.

Purpose of the Study:

  • To investigate the mechanisms of protein import into mitochondria.
  • To identify the molecular components involved in mitochondrial protein translocation.

Main Methods:

  • Utilized in vitro import systems with isolated mitochondria.
  • Employed cell-free synthesis of precursor proteins.
  • Integrated genetic and biochemical approaches.

Main Results:

  • Identified key translocation machineries responsible for protein import.
  • Characterized the multi-component nature of these import systems.

Conclusions:

  • Protein import into mitochondria is a complex, multi-step process.
  • The identified translocation machineries are essential for mitochondrial function and biogenesis.