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Updated: Jul 30, 2026
08:55
Assessment of Submitochondrial Protein Localization in Budding Yeast Saccharomyces cerevisiae
Published on: July 19, 2021
Transport of proteins into mitochondria
K N Truscott1, N Pfanner, W Voos
1Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany.
Reviews of Physiology, Biochemistry and Pharmacology
|June 29, 2001
Summary
Most nuclear-encoded mitochondrial proteins are synthesized in the cytosol and imported into mitochondria via the translocase of the outer membrane (TOM) and inner membrane (TIM) complexes, requiring energy and targeting signals.
Area of Science:
- Cell Biology
- Mitochondrial Biology
- Protein Trafficking
Background:
- Mitochondria, crucial for cellular energy, rely on nuclear-encoded proteins synthesized in the cytosol.
- Efficient mitochondrial protein import is essential for cellular function and requires complex molecular machinery.
Purpose of the Study:
- To elucidate the mechanisms and pathways governing the import of nuclear-encoded proteins into mitochondria.
- To detail the roles of key protein complexes like TOM and TIM in mitochondrial protein translocation.
Main Methods:
- The study reviews the established pathways and molecular players involved in mitochondrial protein import.
- It highlights the necessity of specific targeting signals on preproteins and energy-dependent processes.
Main Results:
- Nuclear-encoded mitochondrial proteins are synthesized as preproteins in the cytosol.
- Translocase of the outer membrane (TOM) and inner membrane (TIM) complexes mediate protein translocation across mitochondrial membranes.
- Protein import pathways are dictated by intrinsic targeting signals and require ATP and membrane potential.
Conclusions:
- Mitochondrial protein import is a multi-step, energy-dependent process involving cytosolic factors, membrane-bound translocases (TOM and TIM), and specific targeting signals.
- Proper folding of imported proteins often necessitates molecular chaperones.
Related Concept Videos
01:45Overview of Protein Sorting and Transport
Eukaryotic cells have different membrane-bound organelles with distinct protein requirements. The process by which proteins are targeted to a specific organelle is called protein sorting.
Protein sorting can be of two types: signal-based sorting and vesicle-based trafficking. In signal-based sorting, specific amino acid sequences called sorting signals target proteins to the proper location inside the cell either via gated transport or by protein translocation. In gated transport, folded...
Protein sorting can be of two types: signal-based sorting and vesicle-based trafficking. In signal-based sorting, specific amino acid sequences called sorting signals target proteins to the proper location inside the cell either via gated transport or by protein translocation. In gated transport, folded...
01:39Mitochondrial 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...
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
01:39Mitochondrial 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 precursors...
Most of the mitochondrial precursors...
01:19Translocation 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,...
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,...
01:34Protein 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...
Transport of mitochondrial precursors across the TIM23 channel is driven by...
01:22Protein Transport to the Thylakoids
Thylakoids are membrane-bound sac-like structures within the chloroplast that serve as sites for photosynthesis. Thylakoid lumen contains many electron transport proteins and is enclosed by a thylakoid membrane rich in the light-harvesting complex. Proteins targeted to the thylakoids are transported as precursors and are sorted by the general TOC/TIC import pathway. Once the precursor reaches the stroma, stromal processing peptidases remove their transit signal and expose thylakoid signal...