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Related Concept Videos

Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

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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,...
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Cotranslational Protein Translocation01:20

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Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the translocation machinery are still conserved between prokaryotes and eukaryotes.
Sec61 channel partners for cotranslational translocation
During cotranslational translocation, the Sec61 channel partners with the signal recognition particle (SRP), the signal recognition particle receptor (SR), and the ribosomes to transport the nascent polypeptide chain...
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Protein Transport to the Thylakoids01:22

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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...
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Energy to Drive Translocation01:37

Energy to Drive Translocation

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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...
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Protein Transport into the Inner Mitochondrial Membrane01:34

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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...
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Protein Translocation Machinery on the ER Membrane01:28

Protein Translocation Machinery on the ER Membrane

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The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
Sec61 protein conducting channel
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Related Experiment Video

Updated: Jul 1, 2025

Detection of Toxin Translocation into the Host Cytosol by Surface Plasmon Resonance
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Anthrax Toxin: Model System for Studying Protein Translocation.

Bryan A Krantz1

  • 1Department of Microbial Pathogenesis, School of Dentistry, University of Maryland, Baltimore, 650 W. Baltimore Street, Baltimore, MD 21201, USA.

Journal of Molecular Biology
|March 8, 2024
PubMed
Summary
This summary is machine-generated.

Anthrax toxin

Keywords:
Brownian ratchetPeptide clampPower strokeProton gradientTranslocase channel

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Area of Science:

  • Biophysics
  • Molecular Biology
  • Biochemistry

Background:

  • Translocase channels are molecular machines that unfold and translocate proteins across membranes.
  • Protein unfolding and translocation require energy due to the thermodynamic stability of folded proteins.
  • Peptide-clamp active sites are often utilized by translocase channels to catalyze unfolding.

Purpose of the Study:

  • To investigate protein translocation using anthrax toxin as a biophysical model system.
  • To elucidate the mechanisms by which the anthrax toxin protective antigen (PA) channel facilitates protein unfolding and translocation.
  • To compare the anthrax toxin translocation mechanism with other known translocase channels.

Main Methods:

  • Utilized anthrax toxin, specifically protective antigen (PA), as a model translocase channel.
  • Investigated the role of peptide-clamp sites (α clamp, ϕ clamp, charge clamp) in the PA channel.
  • Examined the influence of the endosomal proton gradient on protein unfolding and translocation.
  • Analyzed two proposed models for proton gradient-driven translocation: Brownian ratchet and helix-compression mechanisms.

Main Results:

  • Anthrax toxin's protective antigen (PA) functions as an oligomeric translocase channel.
  • Three peptide-clamp sites within the PA channel catalyze unfolding and translocation.
  • The endosomal proton gradient powers the unfolding and translocation process.
  • The Brownian ratchet and helix-compression mechanisms likely operate on different protein secondary structures (β-sheets and α-helices, respectively).

Conclusions:

  • Anthrax toxin provides a valuable model for studying the fundamental principles of protein translocation.
  • Cooperative action of peptide-clamp sites and proton gradient energy drive efficient protein translocation.
  • Distinct translocation mechanisms may be employed for different protein secondary structures within the translocase channel.