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Related Concept Videos

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

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

Insertion of Multi-pass Transmembrane Proteins in the RER

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...
Tail-anchoring of Proteins in the ER Membrane01:45

Tail-anchoring of Proteins in the ER Membrane

Tail-anchored, or TA, proteins are estimated to make up to 3-5% of membrane proteins found in the eukaryotic cell. Such proteins have a single transmembrane domain located approximately 30 amino acid residues upstream from the C-terminal end. As a result, the signal recognition particle (SRP) cannot guide a TA protein to the ER membrane for cotranslational insertion. Hence, they are integrated into the ER membrane post-translationally using their C-terminal end as the anchor. TA proteins...
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.
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...
Directing Proteins to the Rough Endoplasmic Reticulum01:34

Directing Proteins to the Rough Endoplasmic Reticulum

The organelle-specific signaling sequences direct proteins synthesized in the cytosol to their final destination like ER, mitochondria, peroxisomes, etc. Some of the proteins directed to ER are then trafficked via vesicles to other organelles within the cell or the extracellular environment through the Golgi complex. For example, the rough ER synthesizes soluble proteins for transportation to the lysosomes or secretion out of the cell. It can also synthesize transmembrane proteins that can...

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Reconstitution of Msp1 Extraction Activity with Fully Purified Components
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Published on: August 10, 2021

Membrane protein insertion at the endoplasmic reticulum.

Sichen Shao1, Ramanujan S Hegde

  • 1Cell Biology and Metabolism Program, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.

Annual Review of Cell and Developmental Biology
|August 2, 2011
PubMed
Summary

Eukaryotic cell membrane proteins are assembled via two main endoplasmic reticulum pathways: cotranslational and posttranslational. Understanding these protein targeting and insertion mechanisms is crucial for cell biology research.

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Co-Translational Insertion of Membrane Proteins into Preformed Nanodiscs
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Reconstitution of Msp1 Extraction Activity with Fully Purified Components
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Co-Translational Insertion of Membrane Proteins into Preformed Nanodiscs
08:24

Co-Translational Insertion of Membrane Proteins into Preformed Nanodiscs

Published on: November 19, 2020

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Protein Biochemistry

Background:

  • Integral membrane proteins are essential for cellular functions, residing on cell surfaces and within organelles.
  • Their assembly occurs at the endoplasmic reticulum, a critical organelle for protein processing.
  • Two distinct pathways, cotranslational and posttranslational, handle membrane protein insertion.

Purpose of the Study:

  • To review the fundamental concepts and mechanisms of the two major membrane protein insertion pathways.
  • To highlight the biophysical challenges in transporting hydrophobic proteins and their asymmetric integration.
  • To identify complexities and future research directions in membrane protein biogenesis.

Main Methods:

  • Review of existing literature on membrane protein targeting and insertion.
  • Analysis of the conserved cotranslational pathway involving signal recognition particle and Sec61 translocon.
  • Examination of the posttranslational pathway utilizing TRC40/Get3 for tail-anchored proteins.

Main Results:

  • The endoplasmic reticulum employs two parallel pathways for membrane protein assembly: cotranslational and posttranslational.
  • Both pathways address challenges of aqueous transport, selective membrane delivery, and transmembrane domain integration.
  • The TRC40/Get3 pathway represents a specialized route for tail-anchored membrane proteins.

Conclusions:

  • Understanding these pathways is key to deciphering eukaryotic cell protein biogenesis.
  • Further research is needed to resolve complexities in membrane protein insertion.
  • Future studies will focus on overcoming current obstacles in the field.