Related Experiment Video
Updated: Jun 12, 2026
09:01
Measurement of Protein Import Capacity of Skeletal Muscle Mitochondria
Published on: January 7, 2022
Human mitochondrial import receptor Tom70 functions as a monomer
Anna C Y Fan1, Lisandra M Gava, Carlos H I Ramos
1Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
The Biochemical Journal
|May 28, 2010
Summary
The mitochondrial receptor Tom70 functions as a monomer, not a dimer, in protein import. This monomeric form is crucial for efficiently targeting preproteins to mitochondria.
Area of Science:
- Mitochondrial biology
- Protein import mechanisms
- Molecular cell biology
Background:
- Tom70 (translocase of the mitochondrial outer membrane 70) is a key receptor for mitochondrial protein import.
- Tom70 interacts with chaperone complexes (Hsp70, Hsc70, Hsp90) and preproteins via distinct domains.
- The oligomeric state of Tom70, monomeric versus dimeric, has been debated.
Purpose of the Study:
- To investigate the functional oligomeric state of human Tom70 in mitochondrial protein import.
- To determine whether monomeric or dimeric Tom70 is the active form for preprotein targeting.
Main Methods:
- Analytical ultracentrifugation
- Cross-linking assays
- Size-exclusion chromatography
- Multi-angle light scattering
- Site-directed mutagenesis
Main Results:
- The soluble cytosolic fragment of human Tom70 exists in an equilibrium between monomeric and dimeric states.
- A mutation at the predicted dimer interface favored the monomeric form.
- The monomer-favoring mutant showed enhanced activity in preprotein targeting compared to wild-type Tom70.
- Full-length Tom70 on the mitochondrial membrane showed minimal evidence of homodimers.
Conclusions:
- Monomeric Tom70 is the functional form of the receptor for mitochondrial protein import.
- Tom70 homodimers represent a minor, potentially inactive, population.
- The monomeric state facilitates efficient preprotein interaction and targeting.
More Related Videos
08:55Assessment of Submitochondrial Protein Localization in Budding Yeast Saccharomyces cerevisiae
Published on: July 19, 2021
08:55Single-Molecule Imaging of Lateral Mobility and Ion Channel Activity in Lipid Bilayers using Total Internal Reflection Fluorescence (TIRF) Microscopy
Published on: February 17, 2023
Related Concept Videos
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...
01:34Protein 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...
01:39Mitochondrial 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...
01:37Energy 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...
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,...
01:21Structure of Porins
Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel precursors...