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Protein Translocation Machinery on the ER Membrane

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.

Cotranslational Protein Translocation

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...

Post-translational Translocation of Proteins to the RER

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...

Insertion of Single-pass Transmembrane Proteins in the RER

Insertion of Single-pass Transmembrane Proteins in the RER

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...

Bacterial Translocation and Protein Secretion

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...

Protein Transport into the Inner Mitochondrial Membrane

Protein 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...

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Förster Resonance Energy Transfer Mapping: A New Methodology to Elucidate Global Structural Features

Förster Resonance Energy Transfer Mapping: A New Methodology to Elucidate Global Structural Features

Published on: March 16, 2022

The Sec translocase.

David J F du Plessis¹, Nico Nouwen, Arnold J M Driessen

¹Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute and the Zernike Institute for Advanced Materials, University of Groningen, 9751NN Haren, The Netherlands.

Biochimica Et Biophysica Acta

|August 31, 2010

Summary

The bacterial translocon (SecYEG complex) facilitates protein transport across membranes. It works with SecA for posttranslational translocation and ribosome complexes for cotranslational insertion, aided by YidC and SecDF.

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Area of Science:

* Molecular Biology
* Biochemistry
* Cell Biology

Background:

* Bacterial protein translocation across the cytoplasmic membrane is essential for cellular function.
* The SecYEG complex forms the core of the translocon, a conserved protein-conducting channel.
* Ancillary proteins like SecA, YidC, and SecDF assist in protein transport and membrane integration.

Purpose of the Study:

* To review the current understanding of the translocon's structure-function relationship.
* To summarize the interactions between the translocon and its ancillary components.
* To elucidate mechanisms of protein translocation and membrane protein insertion.

Main Methods:

* Review of existing literature on protein translocation and membrane protein insertion.
* Analysis of structural and functional data of the SecYEG complex and associated proteins.
* Integration of knowledge on posttranslational and cotranslational protein transport pathways.

Main Results:

* The SecYEG complex acts as a heterotrimeric channel for protein transport.
* SecA drives ATP-dependent translocation of unfolded polypeptides posttranslationally.
* Ribosome-nascent chain complexes engage for cotranslational membrane protein insertion.
* YidC and SecDF facilitate these processes through transient interactions.

Conclusions:

* The translocon is a dynamic machine with diverse roles in protein trafficking.
* Understanding translocon function is key to deciphering bacterial protein homeostasis.
* Further research into ancillary protein interactions will refine models of membrane protein biogenesis.