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Related Concept Videos

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
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...
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Cotranslational Protein Translocation01:20

Cotranslational Protein Translocation

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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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Insertion of Single-pass Transmembrane Proteins in the RER01:26

Insertion of Single-pass Transmembrane Proteins in the RER

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Integral membrane proteins are proteins adhered to the lipid bilayer of a cell organelle or membrane. They can be of two types: transmembrane integral proteins that span the lipid bilayer and monotopic proteins that are attached to either side of the membrane but do not pass through it.
Integral transmembrane proteins possess transmembrane and extra membrane domains. The transmembrane domains are primarily made of 20-25 hydrophobic amino acids arranged in a helical secondary confirmation. These...
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Post-translational Translocation of Proteins to the RER01:27

Post-translational Translocation of Proteins to the RER

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

Protein Transport into the Inner Mitochondrial Membrane

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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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Insertion of Multi-pass Transmembrane Proteins in the RER01:29

Insertion of Multi-pass Transmembrane Proteins in the RER

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The rough ER membrane synthesizes, assembles, and embeds transmembrane proteins in diverse topologies. These proteins function as transporters or channels and can remain in the ER membrane or are sent to the Golgi complex, lysosome, and cell membrane.
The multipass transmembrane proteins are the type IV integral membrane proteins with multiple topogenic sequences determining their spatial arrangement in the ER membrane. Nearly all multipass proteins lack a cleavable signal sequence and use...
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Diverse mechanisms of translation arrest by a Clostridia ribosome stalling peptide CliM.

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Related Experiment Video

Updated: Dec 29, 2025

Live Cell Calcium Imaging Combined with siRNA Mediated Gene Silencing Identifies Ca2+ Leak Channels in the ER Membrane and their Regulatory Mechanisms
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Sec translocon has an insertase-like function in addition to polypeptide conduction through the channel.

Koreaki Ito1, Naomi Shimokawa-Chiba1, Shinobu Chiba1

  • 1Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan.

F1000Research
|February 7, 2020
PubMed
Summary

The Sec translocon facilitates protein translocation via a channel and also enables *de novo* membrane protein insertion. This insertion occurs at the lateral gate, not the main channel, similar to insertase mechanisms.

Keywords:
Sec61SecYYidCinsertasemembrane proteinsec translocon

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Area of Science:

  • Molecular Biology
  • Membrane Protein Biogenesis
  • Cellular Transport

Background:

  • The Sec translocon is a protein channel crucial for translocating polypeptides across membranes.
  • Its lateral gate facilitates the exit of hydrophobic segments for membrane integration.
  • Existing models partially explain translocon function, particularly regarding hydrophilic polypeptide translocation.

Purpose of the Study:

  • To elucidate the mechanism of *de novo* membrane protein insertion by the Sec translocon.
  • To investigate the role of the lateral gate in *de novo* insertion.
  • To compare *de novo* insertion with insertase mechanisms.

Main Methods:

  • Analysis of recent structural studies on translocon function.
  • Comparative analysis of protein insertion mechanisms.

Main Results:

  • The Sec translocon has a dual function: polypeptide translocation and *de novo* membrane insertion.
  • *De novo* insertion of N-terminal topogenic segments utilizes the lateral gate, not the polypeptide-conducting channel.
  • The *de novo* insertion mechanism resembles that of insertases like YidC and EMC3.

Conclusions:

  • The Sec translocon's *de novo* insertion function is distinct from its translocation channel.
  • The lateral gate is a key site for initiating *de novo* membrane protein insertion.
  • This insertion process involves an intramembrane surface, acting as a halfway point for integration.