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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...

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...

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...

Gram-negative Bacterial Protein Secretion Systems

Gram-negative Bacterial Protein Secretion Systems

Gram-negative bacteria utilize sophisticated protein secretion systems to transport proteins across their double-membrane envelope into the extracellular environment or host cells. Based on their mechanism of action, these systems are classified into one-step and two-step pathways.One-Step Secretion Systems (Types I, III, IV, and VI)One-step secretion systems bypass the periplasm entirely, forming a continuous channel that spans both the inner and outer membranes:Type I Secretion System (T1SS):...

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

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Structure and function of the bacterial Sec translocon.

Vicki A M Gold¹, Franck Duong, Ian Collinson

¹Department of Biochemistry, University of Bristol, Bristol, UK.

Molecular Membrane Biology

|August 22, 2007

Summary

Protein translocation across membranes is governed by a conserved protein complex in all life domains. This review details the mechanism, focusing on bacterial systems using ATP hydrolysis for protein transport through a membrane channel.

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Area of Science:

Molecular Biology
Cell Biology
Biochemistry

Background:

A conserved protein complex facilitates protein secretion and membrane insertion across all domains of life.
Homologues of this complex are found in the endoplasmic reticulum (ER) of eukaryotes.

Purpose of the Study:

To review the current understanding of the protein translocation mechanism.
To integrate genetic, biochemical, and structural findings.

Main Methods:

Review of genetic studies.
Analysis of biochemical data.
Examination of structural findings.

Main Results:

The protein complex forms a channel across the hydrophobic membrane barrier.
Partner proteins assist in maintaining substrate unfolding, targeting, and energy-dependent transport.
Bacterial systems utilize an ATPase for post-translational translocation via ATP hydrolysis.

Conclusions:

The mechanism of protein translocation is conserved but shows domain-specific adaptations.
Understanding this process is crucial for comprehending fundamental cellular functions.