Related Experiment Video
Updated: Jun 10, 2026
09:01
Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
Published on: January 7, 2022
Mitochondrial protein import: from proteomics to functional mechanisms.
Oliver Schmidt1, Nikolaus Pfanner, Chris Meisinger
1Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, Stefan-Meier-Strabetae 17, 79104 Freiburg, Germany. nikolaus.pfanner@biochemie.uni-freiburg.de
Nature Reviews. Molecular Cell Biology
|August 24, 2010
Summary
Mitochondrial protein import pathways are more complex than previously thought. Recent studies reveal new transport routes and interconnected protein networks within mitochondria.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Mitochondria, crucial for cellular energy, contain ~1,000 proteins, mostly imported from the cytosol.
- Established import pathways target the inner membrane and matrix.
- Recent proteomic studies have expanded the understanding of mitochondrial transport.
Purpose of the Study:
- To elucidate novel mechanistic insights into mitochondrial protein import pathways.
- To identify new transport components and pathways.
- To understand the integration of protein translocases into cellular networks.
Main Methods:
- Proteomic analyses to identify new transport components.
- Mechanistic studies to characterize novel import pathways.
- Investigating the integration of translocases within cellular machineries.
Main Results:
- Identification of numerous new transport components.
- Discovery of novel import pathways into the outer membrane and intermembrane space.
- Demonstration that protein translocases are part of dynamic networks.
Conclusions:
- Mitochondrial protein import is more intricate, involving newly discovered pathways and components.
- Protein translocases are integrated into broader cellular networks, including those for bioenergetics and morphology.
- Mitochondrial function is closely linked to other cellular organelles like the endoplasmic reticulum.
Related Concept Videos
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,...
01:39Mitochondrial 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...
01:39Mitochondrial 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...
01:34Protein 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...
01:12Porin Insertion in the Outer Mitochondrial Membrane
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...
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...
01:37Energy 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...
Generally, polypeptides are unfolded by two distinct...