post-translational protein targeting to membrane, translocation

Definition

Target type: biologicalprocess

The process in which a protein translocates through the ER membrane posttranslationally. [PMID:12518317, PMID:8707814]

Post-translational protein targeting to membranes, also known as translocation, is a crucial process in cellular function, ensuring proteins are delivered to their correct destinations within the cell, particularly to the endoplasmic reticulum (ER) membrane. Here's a detailed breakdown of the process:

1. **Synthesis and Recognition:** Proteins destined for the ER are synthesized by ribosomes in the cytoplasm. These proteins typically possess a signal sequence, a short stretch of amino acids at their N-terminus, which acts as a "zip code" for targeting to the ER.

2. **Signal Recognition Particle (SRP):** The SRP, a cytosolic ribonucleoprotein complex, recognizes and binds to the signal sequence on the nascent polypeptide chain. This binding event temporarily halts protein synthesis.

3. **SRP Receptor:** The SRP-ribosome complex then encounters the SRP receptor, a transmembrane protein embedded in the ER membrane. The SRP receptor facilitates the docking of the ribosome to the translocon, a protein channel within the ER membrane.

4. **Translocation Channel:** The translocon, composed of Sec61α, Sec61β, and Sec61γ subunits, forms a pore through the ER membrane. The ribosome, with its attached polypeptide chain, associates with the translocon.

5. **Signal Sequence Cleavage:** As the polypeptide chain translocates through the translocon, the signal sequence is recognized and cleaved off by a signal peptidase, an enzyme residing within the ER lumen.

6. **Protein Folding and Modification:** Once inside the ER lumen, the translocated protein undergoes folding and post-translational modifications, such as glycosylation, disulfide bond formation, and chaperone-assisted protein folding.

7. **Targeting to Specific Membrane Locations:** Some proteins destined for the ER membrane may contain transmembrane domains that anchor them within the lipid bilayer. These domains are often hydrophobic and can interact with the lipid environment of the membrane.

8. **Protein Sorting and Trafficking:** Following translocation and modification, the protein may be further sorted and trafficked to other cellular compartments, such as the Golgi apparatus, lysosomes, or plasma membrane, via vesicles and other transport mechanisms.

9. **Quality Control:** During and after translocation, protein quality control mechanisms are in place to ensure proper folding and assembly. Misfolded or improperly assembled proteins are targeted for degradation.

This intricate process of post-translational protein targeting to membranes ensures that proteins are delivered to their correct locations within the cell, enabling proper function and maintaining cellular homeostasis.'
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Proteins (2)

Compounds (15)