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Related Concept Videos

Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

9.7K
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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Protein Transport into the Inner Mitochondrial Membrane01:34

Protein Transport into the Inner Mitochondrial Membrane

4.4K
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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Porin Insertion in the Outer Mitochondrial Membrane01:12

Porin Insertion in the Outer Mitochondrial Membrane

3.9K
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

2.4K
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: Nov 8, 2025

Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
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Mitochondrial protein import as a quality control sensor.

Sebabrata Maity1,2, Oishee Chakrabarti1,2

  • 1Biophysics & Structural Genomics Division, Saha Institute of Nuclear Physics, Kolkata, 700064, India.

Biology of the Cell
|April 19, 2021
PubMed
Summary

Mitochondrial protein import is crucial for cellular health, involving complex machinery for precursor delivery. Defects in this process can lead to diseases like neurodegeneration and cancer.

Keywords:
Intracellular compartmentalisationMitochondriaProtein degradation/proteases

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Mitochondria, essential for cellular metabolism and homeostasis, rely on nuclear-encoded proteins synthesized in the cytosol.
  • These precursor proteins require sophisticated import machineries to cross mitochondrial membranes.

Purpose of the Study:

  • To provide a comprehensive overview of mitochondrial protein import machinery.
  • To elucidate the role of this machinery in cellular quality control.
  • To discuss the pathological implications of import defects in diseases.

Main Methods:

  • Review of existing literature on mitochondrial protein import pathways.
  • Analysis of the interaction between import machineries and other cellular complexes.
  • Discussion of transcriptomic and proteomic changes associated with import defects.

Main Results:

  • Mitochondrial protein import involves complex recognition, translocation, and sorting mechanisms.
  • Import machineries interact with respiratory chain complexes and membrane architecture proteins.
  • Defective import leads to precursor accumulation, aggregation, and cellular stress responses.

Conclusions:

  • Mitochondrial protein translocation is vital for organelle biogenesis, bioenergetics, and quality control.
  • Dysfunctional import contributes to cellular dysfunction and disease pathogenesis.
  • Understanding these pathways is key to addressing neurodegeneration and cancer.