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A role for Tim21 in membrane-potential-dependent preprotein sorting in mitochondria
Martin van der Laan1, Nils Wiedemann, David U Mick
1Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany.
Current Biology : CB
|November 23, 2006
Summary
Mitochondrial protein sorting is enhanced by a direct interaction between the presequence translocase and respiratory chain complexes. This cooperation stimulates protein insertion into the inner mitochondrial membrane.
Area of Science:
- Mitochondrial biology
- Cellular respiration
- Protein import and targeting
Background:
- The mitochondrial inner membrane is crucial for cellular energy production and protein homeostasis.
- Respiratory chain complexes generate membrane potential essential for ATP synthesis and protein import.
- Preprotein translocases were thought to utilize membrane potential passively without direct interaction with respiratory complexes.
Purpose of the Study:
- To investigate the physical interaction between preprotein translocases and respiratory chain complexes.
- To elucidate the role of specific subunits in mediating this interaction and its functional consequences.
- To challenge the prevailing model of independent function of translocases and respiratory chain.
Main Methods:
- Co-immunoprecipitation assays to detect protein-protein interactions.
- Blue-native PAGE to analyze respiratory chain complex assembly and interactions.
- In vitro import assays to measure preprotein translocation efficiency.
- Site-directed mutagenesis to identify key residues involved in Tim21 function.
Main Results:
- Demonstrated a direct physical interaction between the presequence translocase and respiratory chain complexes.
- Identified Tim21, a subunit of the presequence translocase, as a key mediator of this interaction.
- Showed that Tim21 recruits proton-pumping respiratory chain complexes, enhancing preprotein insertion.
- Established that this cooperation promotes membrane-potential-dependent protein sorting into the inner mitochondrial membrane.
Conclusions:
- The presequence translocase actively cooperates with the respiratory chain, challenging previous assumptions.
- Tim21 acts as a crucial link, coupling protein sorting with energy transduction.
- This interaction represents a novel mechanism for coordinating mitochondrial function and protein import.
Related Concept Videos
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...
01:19Translocation 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...
01:37Energy 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...
01:21Structure 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...