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Related Concept Videos

Mitochondrial Precursor Proteins01:39

Mitochondrial Precursor Proteins

3.9K
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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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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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,...
13.7K
Energy to Drive Translocation01:37

Energy to Drive Translocation

2.9K
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...
2.9K
Protein Transport into the Inner Mitochondrial Membrane01:34

Protein Transport into the Inner Mitochondrial Membrane

5.1K
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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Electron Transport Chain: Complex I and II01:46

Electron Transport Chain: Complex I and II

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The mitochondrial electron transport chain (ETC) is the main energy generation system in the eukaryotic cells. However, mitochondria also produce cytotoxic reactive oxygen species (ROS) due to the large electron flow during oxidative phosphorylation. While Complex I is one of the primary sources of superoxide radicals, ROS production by Complex II is uncommon and may only be observed in cancer cells with mutated complexes.
ROS generation is regulated and maintained at moderate levels necessary...
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Author Spotlight: Decoding Mitochondrial Aging
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Author Spotlight: Decoding Mitochondrial Aging

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Mitochondrial Precursor Overaccumulation Stress.

Liam P Coyne1, Xin Jie Chen2

  • 1Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.

Annual Review of Biochemistry
|March 20, 2026
PubMed
Summary
This summary is machine-generated.

Mitochondrial precursor overaccumulation stress (mPOS) arises from impaired protein import, causing toxic cytosolic protein buildup. This stress impacts cell signaling, survival, and disease, independent of energy production deficits.

Keywords:
diseasemPOSmitochondriamitochondrial precursor overaccumulation stressprotein importproteostasisstress signaling

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Assessment of Open Probability of the Mitochondrial Permeability Transition Pore in the Setting of Coenzyme Q Excess
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Area of Science:

  • Cellular Biology
  • Mitochondrial Biology
  • Stress Response

Background:

  • Mitochondrial damage causes cellular stress beyond energy deficits.
  • Mitochondrial precursor overaccumulation stress (mPOS) is a newly identified stress.
  • mPOS results from impaired mitochondrial protein import, leading to toxic precursor accumulation in the cytosol.

Purpose of the Study:

  • To review the discovery and significance of mPOS.
  • To discuss mPOS's role in mitochondria-induced stress signaling pathways.
  • To explore mPOS's impact on cell demise, human disease, and survival.

Main Methods:

  • Literature review of mPOS discovery and research.
  • Analysis of mPOS's connection to cellular signaling pathways.
  • Examination of mPOS's role in cell death and disease pathogenesis.

Main Results:

  • mPOS is characterized by the cytosolic accumulation of unimported mitochondrial proteins.
  • mPOS imposes a significant proteostatic burden, analogous to ER stress.
  • mPOS influences major mitochondria-induced stress signaling pathways.

Conclusions:

  • mPOS affects cell fitness and survival independently of bioenergetic deficits.
  • mPOS may represent a pathogenic mechanism in mitochondriopathies and aging-related diseases.
  • Understanding mPOS offers new insights into mitochondrial stress and disease.