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Related Concept Videos

Post-translational Translocation of Proteins to the RER01:27

Post-translational Translocation of Proteins to the RER

A sizable fraction of proteins destined for ER are first synthesized in the cell cytosol and then transported across the ER membrane–a process called post-translational translocation. Similar to cotranslationally translocated proteins, these proteins also use the Sec translocon complex to enter the ER lumen.
Targeting proteins to the ER
Hsp40 and Hsp70 chaperone molecules bind the translated proteins in the cytosol to prevent their folding. The chaperone binding helps to keep the signal...
Translocation of Proteins into the Mitochondria01:19

Translocation 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,...
Cotranslational Protein Translocation01:20

Cotranslational Protein Translocation

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

Protein Translocation Machinery on the ER Membrane

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
In eukaryotes, the translocon complex comprises a core heterotrimeric translocator channel called the Sec61 complex. This channel includes three transmembrane proteins, Sec61α, Sec61β, and Sec61γ, and is the largest subunit of the translocon complex.
Protein Transport to the Thylakoids01:22

Protein Transport to the Thylakoids

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...
Bacterial Translocation and Protein Secretion01:26

Bacterial Translocation and Protein Secretion

Bacterial protein secretion involves translocation systems to ensure proteins reach their designated locations, including the plasma membrane, periplasm, outer membrane, or the external environment. These translocation systems are vital for bacterial physiology, supporting processes like membrane assembly, enzymatic activity in the periplasm, and interactions with the external environment. The division of labor between Sec and Tat pathways ensures efficiency in handling proteins with diverse...

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Related Experiment Video

Updated: Jun 22, 2026

Monitoring the Assembly of a Secreted Bacterial Virulence Factor Using Site-specific Crosslinking
11:33

Monitoring the Assembly of a Secreted Bacterial Virulence Factor Using Site-specific Crosslinking

Published on: December 17, 2013

Polypeptide translocation by the AAA+ ClpXP protease machine.

Sarah R Barkow1, Igor Levchenko, Tania A Baker

  • 1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Chemistry & Biology
|June 25, 2009
PubMed
Summary
This summary is machine-generated.

The ClpXP protease machine efficiently degrades diverse protein substrates by unfolding them, indicating minimal chemical features are needed for translocation. This suggests the ClpX unfoldase pore is highly elastic.

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Last Updated: Jun 22, 2026

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Published on: December 17, 2013

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Proteostasis

Background:

  • The AAA+ ClpXP protease complex plays a crucial role in protein degradation and cellular proteostasis.
  • ClpX, an AAA+ ATPase, utilizes ATP hydrolysis to unfold and translocate proteins into the ClpP protease core for degradation.

Purpose of the Study:

  • To investigate the essential polypeptide features required for translocation by the ClpX machine.
  • To determine the substrate specificity and translocation mechanism of the ClpXP protease.

Main Methods:

  • Degradation assays using diverse synthetic peptide substrates with varying chemical properties (chirality, size, polarity).
  • Analysis of ClpXP degradation of a stably folded protein with homopolymeric tracts of glycine, proline, and lysine.
  • Investigation of translocation without a peptide N-terminus and with extended peptide bonds.

Main Results:

  • ClpXP efficiently degrades synthetic peptides regardless of significant differences in side-chain chirality, size, and polarity.
  • Translocation and degradation occur even with modified peptide bonds (lacking N-H) and extended spacing between peptide bonds.
  • ClpXP effectively degrades a folded protein when coupled with homopolymeric tracts of glycine, proline, or lysine.

Conclusions:

  • Minimal chemical features of a polypeptide chain are sufficient for translocation and unfolding by the ClpX machine.
  • The translocation pore of ClpX is highly elastic, accommodating a wide range of chemical groups.
  • This elasticity is likely a conserved feature among AAA+ unfoldases involved in protein processing.