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Related Concept Videos

Energy to Drive Translocation01:37

Energy to Drive Translocation

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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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Protein Transport into the Inner Mitochondrial Membrane01:34

Protein Transport into the Inner Mitochondrial Membrane

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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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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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The Inner Mitochondrial Membrane01:28

The Inner Mitochondrial Membrane

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The inner mitochondrial membrane is the primary site of ATP synthesis. The inner membrane domain that forms a smooth layer adjacent to the outer membrane is called the inner boundary membrane. This domain contains membrane transporters that drive metabolites in and out of the mitochondria.  In contrast, the inner membrane network that invaginates into the matrix space is called the cristae membrane. This domain accounts for principle mitochondrial function as it accommodates the protein...
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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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Related Experiment Video

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Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
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Two distinct membrane potential-dependent steps drive mitochondrial matrix protein translocation.

Alexander Benjamin Schendzielorz1, Christian Schulz1, Oleksandr Lytovchenko1

  • 1Department of Cellular Biochemistry, University Medical Center Göttingen, Georg-August-Universität Göttingen, 37073 Göttingen, Germany.

The Journal of Cell Biology
|December 25, 2016
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Summary

Mitochondrial protein import involves two membrane potential-driven steps. A novel step, dependent on Pam17 and membrane potential, is crucial for translocating mature mitochondrial proteins into the matrix.

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Area of Science:

  • Mitochondrial biology
  • Protein import
  • Cellular transport

Background:

  • Mitochondrial protein import relies on the membrane potential (Δψ) and Hsp70 motor.
  • The TIM23 complex facilitates precursor translocation across the inner mitochondrial membrane.

Purpose of the Study:

  • To investigate the distinct dependencies of mitochondrial matrix proteins on the membrane potential.
  • To identify novel energy-dependent steps in precursor translocation.

Main Methods:

  • Analysis of precursor translocation under varying membrane potential conditions.
  • Investigating the role of Pam17 and Tim50 in precursor import.
  • Characterizing the energy requirements of different translocation stages.

Main Results:

  • Mitochondrial matrix proteins exhibit varied dependencies on the membrane potential.
  • Precursor hypersensitivity to reduced Δψ is linked to the mature protein, not the presequence.
  • Pam17, recruited by Tim50, mediates a Δψ-dependent import step for hypersensitive precursors.

Conclusions:

  • Two distinct Δψ-driven steps energize precursor passage across the inner mitochondrial membrane.
  • A novel Δψ- and Pam17-dependent import step occurs between presequence translocation and Hsp70 motor activity.