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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,...
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...
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...
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...

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Related Experiment Video

Updated: May 16, 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 synthesis, import, and assembly.

Thomas D Fox1

  • 1Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.

Genetics
|December 6, 2012
PubMed
Summary
This summary is machine-generated.

Mitochondria, essential for cell life and energy, utilize complex protein import pathways. This study details how yeast mitochondrial proteins are synthesized and directed to their correct cellular locations.

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Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
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Published on: January 7, 2022

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Assessment of Submitochondrial Protein Localization in Budding Yeast Saccharomyces cerevisiae
08:55

Assessment of Submitochondrial Protein Localization in Budding Yeast Saccharomyces cerevisiae

Published on: July 19, 2021

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Mitochondria are vital organelles in eukaryotic cells, crucial for viability and respiratory growth.
  • They possess a complex structure with distinct compartments: matrix, inner membrane, intermembrane space, and outer membrane.
  • Approximately 1000 proteins reside in mitochondria, with eight synthesized within the matrix.

Purpose of the Study:

  • To elucidate the intricate pathways governing the import and targeting of cytoplasmically synthesized mitochondrial proteins in yeast.
  • To understand how these proteins are directed to specific compartments, membranes, and topological orientations within the mitochondrion.
  • To investigate the role of localized mRNA translation in mitochondrial protein targeting.

Main Methods:

  • Analysis of protein import and targeting mechanisms in budding yeast.
  • Investigation of the role of the translocase of the outer membrane complex.
  • Study of divergent sorting pathways in the intermembrane space.
  • Examination of mitochondrial genome maintenance and expression proteins.

Main Results:

  • Most cytoplasmically synthesized mitochondrial proteins transit the translocase of the outer membrane.
  • Divergent pathways in the intermembrane space sort proteins to various mitochondrial compartments.
  • A subset of mitochondrial proteins (25%) are involved in organellar genome expression, including seven membrane proteins crucial for respiratory complex assembly.

Conclusions:

  • Yeast mitochondria employ sophisticated, multi-step pathways for protein import and localization.
  • Targeting efficiency relies on specific protein machinery and compartmental sorting mechanisms.
  • Mitochondrial protein import is fundamental for cellular respiration and overall cell function.