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Mitochondrial Precursor Proteins

Mitochondrial Precursor Proteins

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...

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,...

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...

The Proteasome

The Proteasome

Eukaryotic cells can degrade proteins through several pathways. One of the most important among these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. This involves participation of a series of enzymes including— E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...

The Proteasome

The Proteasome

Eukaryotic cells can degrade proteins through several pathways. One of the most important amongst these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. A series of enzymes carry out the ubiquitination of the target proteins - E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...

The Proteasome

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Related Experiment Video

Updated: Mar 7, 2026

Cycloheximide Chase Analysis of Protein Degradation in Saccharomyces cerevisiae

Cycloheximide Chase Analysis of Protein Degradation in Saccharomyces cerevisiae

Published on: April 18, 2016

The novel mitochondrial matrix protease Ste23 is required for efficient presequence degradation and processing.

Asli Aras Taskin^1,2,3, Cansu Kücükköse^1,2, Nils Burger^1,4

¹Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, 79104 Freiburg, Germany.

Molecular Biology of the Cell

|February 24, 2017

Summary

Mitochondrial protein import relies on peptide degradation. Researchers discovered Ste23, a novel protease, that cooperates with Cym1 to efficiently clear peptides, ensuring proper mitochondrial function.

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Last Updated: Mar 7, 2026

Cycloheximide Chase Analysis of Protein Degradation in Saccharomyces cerevisiae

Cycloheximide Chase Analysis of Protein Degradation in Saccharomyces cerevisiae

Published on: April 18, 2016

Reconstitution of Msp1 Extraction Activity with Fully Purified Components

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Published on: August 10, 2021

Assessment of Submitochondrial Protein Localization in Budding Yeast Saccharomyces cerevisiae

Assessment of Submitochondrial Protein Localization in Budding Yeast Saccharomyces cerevisiae

Published on: July 19, 2021

Area of Science:

Mitochondrial biology
Protease function
Protein import and degradation

Background:

Mitochondrial precursor proteins are imported from the cytosol via N-terminal presequences.
These presequences are cleaved by the mitochondrial processing protease (MPP) in the matrix.
Efficient degradation of cleaved presequence peptides is crucial to prevent feedback inhibition of MPP and accumulation of immature proteins.

Purpose of the Study:

To identify novel factors involved in mitochondrial peptide degradation.
To elucidate the cooperative mechanisms of presequence peptide clearance.
To understand the role of novel proteases in maintaining mitochondrial homeostasis.

Main Methods:

Yeast genetics and molecular biology techniques.
Protease activity assays.
Analysis of mitochondrial protein import and processing.

Main Results:

Identification of Ste23, a novel mitochondrial matrix protease, as essential for efficient peptide degradation.
Demonstration that Ste23 is a homologue of human insulin-degrading enzyme.
Evidence of tight cooperation between Ste23 and Cym1 in degrading presequence peptides.

Conclusions:

Ste23 plays a critical role in the degradation of mitochondrial presequence peptides.
The cooperative action of Ste23 and Cym1 is essential for the proper functioning of the mitochondrial presequence processing machinery.
Dysfunctional peptide degradation can lead to mitochondrial dysfunction, highlighting the importance of this pathway.