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Mitochondrial Protein Sorting

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...

Protein Transport into the Inner Mitochondrial Membrane

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...

Translocation of Proteins into the Mitochondria

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,...

The Inner Mitochondrial Membrane

The Inner Mitochondrial Membrane

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...

Energy to Drive Translocation

Energy to Drive Translocation

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...

Mitochondrial Membranes

Mitochondrial Membranes

A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...

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Related Experiment Video

Updated: Jul 11, 2025

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

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Mitochondrial entry gate as regulatory hub.

Fabian den Brave¹, Nikolaus Pfanner², Thomas Becker¹

¹Institute of Biochemistry and Molecular Biology, Faculty of Medicine, University of Bonn, 53115 Bonn, Germany.

Biochimica Et Biophysica Acta. Molecular Cell Research

|November 11, 2023

Summary

This summary is machine-generated.

Mitochondria import proteins via the translocase of the outer membrane (TOM complex). This complex acts as a hub, regulating protein import and quality control within cellular proteostasis.

Keywords:

Mitochondria Protein sorting Proteostasis Quality control Stress response TOM complex

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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:

Mitochondrial biology
Cellular protein homeostasis

Background:

Mitochondria require the import of over 1000 precursor proteins from the cytosol.
The translocase of the outer membrane (TOM complex) is the primary gateway for mitochondrial protein import.

Purpose of the Study:

To elucidate the regulatory mechanisms of the TOM complex in protein import.
To understand how TOM integrates mitochondrial biogenesis into cellular proteostasis.

Main Methods:

Investigating the molecular coupling and modification of TOM subunits.
Analyzing the role of TOM complex as a regulatory hub.

Main Results:

TOM subunit modification and coupling are key to controlling protein import.
The TOM complex integrates mitochondrial protein import and quality control with cellular signaling.

Conclusions:

The TOM complex is a critical regulatory hub for mitochondrial protein import.
Mitochondrial protein biogenesis and quality control are tightly linked to the cellular proteostasis network via the TOM complex.