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Related Concept Videos

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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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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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

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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Structure of Porins01:21

Structure of Porins

4.1K
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...
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Related Experiment Video

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Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
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Mitochondrial Machineries for Protein Import and Assembly.

Nils Wiedemann1, Nikolaus Pfanner1

  • 1Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, and BIOSS Centre for Biological Signaling Studies, University of Freiburg, 79104 Freiburg, Germany; email: nils.wiedemann@biochemie.uni-freiburg.de , nikolaus.pfanner@biochemie.uni-freiburg.de.

Annual Review of Biochemistry
|March 17, 2017
PubMed
Summary

Mitochondria import over 1,000 proteins via five pathways. Understanding these dynamic protein import machineries is key to cellular homeostasis and organelle function.

Keywords:
inner membranemitochondrial architectureouter membranepreproteinprotein sortingtranslocase

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Area of Science:

  • Cell Biology
  • Mitochondrial Biology
  • Molecular Mechanisms

Background:

  • Mitochondria are vital organelles regulating cellular metabolism and homeostasis.
  • Over 1,000 mitochondrial proteins are synthesized in the cytosol and imported via five distinct pathways.
  • Mitochondrial protein import involves complex machineries within membranes and aqueous compartments.

Purpose of the Study:

  • To discuss the versatility and dynamic organization of mitochondrial protein import machineries.
  • To highlight the interconnectedness of protein translocases with other cellular functions.
  • To emphasize the importance of understanding molecular mechanisms for organelle biogenesis and dynamics.

Main Methods:

  • Review of existing literature on mitochondrial protein import.
  • Analysis of the mechanisms of protein recognition, translocation, and sorting.
  • Discussion of the integration of import machineries with cellular energetics and quality control.

Main Results:

  • Mitochondrial protein import exhibits remarkable variability in recognition, translocation, and sorting mechanisms.
  • Protein translocases are interconnected, forming a network with functions in energetics, membrane organization, and quality control.
  • The import machinery is dynamically organized, not operating as isolated entities.

Conclusions:

  • Elucidating mitochondrial protein translocation mechanisms is crucial for understanding organelle biogenesis and function.
  • The dynamic and interconnected nature of import machineries influences mitochondrial homeostasis.
  • Further research into these molecular mechanisms is essential for a comprehensive understanding of mitochondrial dynamics.