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Updated: Jun 9, 2026
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Assessment of Submitochondrial Protein Localization in Budding Yeast Saccharomyces cerevisiae
Published on: July 19, 2021
The structural plasticity of Tom71 for mitochondrial precursor translocations
Jingzhi Li1, Wenjun Cui, Bingdong Sha
1Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Summary
Mitochondrial protein import relies on Tom71 receptors. New structures reveal Tom71
Area of Science:
- Mitochondrial biology
- Protein transport
- Structural biology
Background:
- Mitochondrial precursors are imported via the translocase of the outer membrane (TOM) complex.
- Tom70/Tom71 receptors on the mitochondrial surface bind Hsp70/Hsp90-escorted precursors.
- Previous Tom71 structures suggested an open conformation upon Hsp70/Hsp90 binding.
Purpose of the Study:
- To elucidate the structural dynamics of Tom71 during precursor binding.
- To investigate the conformational changes of Tom71 in complex with Hsp70 C-terminus.
- To understand how structural plasticity influences substrate accommodation.
Main Methods:
- X-ray crystallography to determine the structure of the Tom71-Hsp70 C-terminus complex.
- Comparison of the new crystal structure with previously determined Tom71 structures.
- Analysis of domain rearrangements and their impact on the binding pocket.
Main Results:
- A novel crystal structure of Tom71 in an 'intermediate conformation' was obtained.
- The N-terminal domain of Tom71 rotated 12 degrees towards the C-terminal domain.
- These domain rearrangements altered surface hydrophobicity and the precursor-binding pocket volume.
Conclusions:
- Tom70/Tom71 receptors exhibit structural plasticity, transitioning between intermediate and open conformations.
- This conformational flexibility allows Tom70/Tom71 to bind diverse precursor proteins for mitochondrial import.
- Understanding these dynamics is crucial for comprehending mitochondrial protein translocation.
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...
01:19Translocation 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,...
01:37Energy 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...
01:34Protein 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...
01:21Structure 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...