GO:0006620 post-translational protein targeting to endoplasmic reticulum membrane: Protein Targeting Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0006620 describes the SRP-independent route by which fully synthesized proteins are delivered to the ER membrane after translation.
• The pathway handles tail-anchored proteins and small secretory proteins that escape co-translational SRP targeting.
• Key machinery includes the Get3/TRC40 chaperone cascade, the Get1/Get2 receptor, and the Sec61 translocon.
• The EMC complex rectifies membrane protein topology and supports post-translational insertion.
• Defects in this pathway are linked to neurodegeneration, CFTR trafficking disorders, and cholesterol-related inflammasome signaling.
• CRISPR knockout, point-mutation, knock-in, and overexpression models enable causal dissection of this targeting route.
Description
Post-translational protein targeting to the endoplasmic reticulum membrane (GO:0006620) is the process by which proteins are delivered to the ER membrane after their synthesis is complete. Unlike co-translational translocation, where the ribosome docks onto the ER as the polypeptide emerges, this pathway releases fully synthesized proteins into the cytosol, where chaperones maintain them in an unfolded state before membrane insertion. This route is essential for tail-anchored proteins and certain secretory proteins that cannot engage the signal recognition particle (SRP) during translation. The pathway ensures that membrane proteins acquire correct topology and function, and its dysfunction is increasingly implicated in human disease. Researchers study GO:0006620 to understand ER homeostasis, membrane protein biogenesis, and therapeutic targets for neurodegeneration and trafficking disorders.
post-translational protein targeting to endoplasmic reticulum membrane At A Glance
| GO ID | GO:0006620 |
|---|---|
| GO term | post-translational protein targeting to endoplasmic reticulum membrane |
| Ontology | biological_process |
| Synonym | posttranslational protein targeting to ER membrane; SRP-independent endoplasmic reticulum protein-membrane targeting |
| Major function | Delivery of fully synthesized proteins to the ER membrane for insertion or translocation |
| Key machinery | Get3/TRC40 chaperone cascade, Get1/Get2 receptor, Sec61 translocon, EMC complex |
| Substrates | Tail-anchored proteins and small secretory proteins lacking SRP dependence |
| Cellular context | ER membrane, cytosol, mitochondria-associated ER membranes |
What Is GO:0006620?
GO:0006620 is defined as the targeting of proteins to the ER membrane that occurs after their translation. In this process, secretory proteins are synthesized entirely on free cytosolic ribosomes and then released into the cytosol, where chaperones bind them to keep them unfolded; they are subsequently translocated across the ER membrane. This SRP-independent mechanism contrasts with co-translational targeting and is critical for tail-anchored membrane proteins and other substrates that evade the signal recognition particle pathway.
Why Is post-translational protein targeting to endoplasmic reticulum membrane Important in Cell Biology?
GO:0006620 is essential because it provides a parallel, SRP-independent route for membrane protein biogenesis, ensuring that tail-anchored proteins and other post-translationally targeted substrates reach the ER. This pathway maintains ER function, calcium signaling, and lipid homeostasis, and its disruption contributes to neurodegeneration, cystic fibrosis, and inflammatory diseases.
• Enables biogenesis of tail-anchored proteins that regulate apoptosis, vesicle trafficking, and membrane fusion.
• Supports ER homeostasis by delivering proteins that maintain calcium signaling and organelle contact sites.
• Contributes to cholesterol homeostasis through SCAP-SREBP2 and NLRP3 inflammasome regulation.
• Its dysfunction is linked to neurodegenerative diseases via altered mitochondria-associated ER membranes.
• Plays a role in CFTR folding and trafficking, relevant to cystic fibrosis.
• Provides a target for therapeutic intervention in protein misfolding disorders.
• The EMC complex rectifies membrane protein topology, a quality-control step in this pathway.
• Sec61 translocon mediates the final translocation step for post-translationally targeted proteins.
• Chaperone cascades (Get3/TRC40) ensure substrate solubility and delivery specificity.
• CRISPR screens can identify novel regulators of this pathway.
What Happens During post-translational protein targeting to endoplasmic reticulum membrane?
Substrate recognition and chaperone binding
In simple terms: Fully made proteins are kept unfolded by chaperones so they can be delivered to the ER.
After synthesis on free cytosolic ribosomes, tail-anchored proteins and other post-translational substrates are captured by chaperones such as Get3/TRC40, which maintain them in an unfolded state and prevent aggregation. This step is SRP-independent and ensures that hydrophobic transmembrane domains remain soluble in the cytosol.
Delivery to the ER membrane receptor
In simple terms: The chaperone carries the protein to a receptor on the ER surface.
The Get3/TRC40-substrate complex docks at the ER membrane via the Get1/Get2 receptor, which facilitates substrate release and insertion into the lipid bilayer. This delivery step is a key checkpoint for tail-anchored protein biogenesis.
Membrane insertion and topology establishment
In simple terms: The protein is inserted into the ER membrane in the correct orientation.
Following release from the chaperone, the substrate is inserted into the ER membrane. The EMC complex rectifies the topology of multipass membrane proteins, ensuring correct orientation and function. For secretory proteins, translocation across the membrane is mediated by the Sec61 translocon.
Quality control and ER homeostasis
In simple terms: The ER checks that proteins are correctly folded and inserted.
Misfolded or misinserted proteins are recognized by ER quality control machinery. The EMC complex and Sec61 translocon coordinate with chaperones to maintain ER homeostasis, and defects in this process are linked to diseases such as cystic fibrosis and neurodegeneration.
Key Genes Involved in GO:0006620 post-translational protein targeting to endoplasmic reticulum membrane
The following genes and proteins are central to post-translational protein targeting to the ER membrane, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| GET3 | ATPase chaperone that binds tail-anchored proteins and delivers them to the ER | Knockout studies reveal substrate specificity and chaperone cascade |
| GET1 | ER membrane receptor subunit for Get3-substrate complex | Mutations affect tail-anchored protein insertion |
| GET2 | ER membrane receptor subunit for Get3-substrate complex | Required for efficient post-translational targeting |
| SEC61A1 | Core channel of the Sec61 translocon for protein translocation | Point mutations alter translocation efficiency |
| SEC61B | Accessory subunit of Sec61 complex | Knockout affects secretory protein targeting |
| SEC61G | Accessory subunit of Sec61 complex | Modulates translocon function |
| EMC1 | Subunit of ER membrane protein complex (EMC) | Knockout causes membrane protein topology defects |
| EMC2 | Subunit of EMC complex | Required for multipass membrane protein biogenesis |
| EMC3 | Subunit of EMC complex | Mutations affect ER membrane protein insertion |
| EMC4 | Subunit of EMC complex | Involved in quality control of membrane proteins |
| EMC5 | Subunit of EMC complex | Supports post-translational insertion |
| EMC6 | Subunit of EMC complex | Linked to ER homeostasis |
| EMC7 | Subunit of EMC complex | Modulates EMC function |
| EMC8 | Subunit of EMC complex | Required for EMC assembly |
| EMC9 | Subunit of EMC complex | Involved in membrane protein quality control |
| EMC10 | Subunit of EMC complex | Supports EMC complex stability |
| CFTR | Chloride channel that folds and traffics through the ER | Mutations cause cystic fibrosis; model for ER trafficking |
How Is post-translational protein targeting to endoplasmic reticulum membrane Regulated?
The pathway is regulated by chaperone availability, ATP levels, and ER membrane composition. The Get3/TRC40 chaperone cascade is ATP-dependent and ensures substrate delivery. The EMC complex and Sec61 translocon are subject to quality control and ER stress responses. Additionally, protein S-palmitoylation controls mitochondria-associated ER membranes, influencing targeting and calcium signaling. Cholesterol homeostasis via SCAP-SREBP2 integrates with NLRP3 inflammasome activation, linking metabolic state to ER targeting.
post-translational protein targeting to endoplasmic reticulum membrane and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CFTR | Cystic fibrosis; ER folding and trafficking | Knock-in of F508del mutation in cell lines |
| SIGMAR1 | Neurodegeneration; ER-mitochondrion Ca2+ signaling | Knockout and point-mutation models |
| SCAP | Cholesterol homeostasis and inflammasome activation | Knockout in macrophages |
| SREBP2 | Metabolic and inflammatory diseases | Overexpression and knockout models |
| GET3 | Tail-anchored protein biogenesis defects | Knockout and point-mutation in human cells |
Neurodegenerative diseases
Disruption of post-translational targeting to the ER membrane affects mitochondria-associated ER membranes and calcium signaling, contributing to neurodegeneration. The sigma-1 receptor chaperone at the ER-mitochondrion interface regulates Ca2+ signaling and cell survival, and its dysfunction is implicated in neurodegenerative disorders.
Cystic fibrosis and trafficking disorders
CFTR folding and trafficking from the ER to the plasma membrane is a paradigm for post-translational targeting defects. Mutations in CFTR cause cystic fibrosis, and understanding its ER processing provides therapeutic insights.
Inflammatory and metabolic diseases
The SCAP-SREBP2 pathway integrates cholesterol biosynthetic signaling with NLRP3 inflammasome activation, linking ER targeting and cholesterol homeostasis to inflammation. Dysregulation of this axis contributes to metabolic and inflammatory diseases.
From post-translational protein targeting to endoplasmic reticulum membrane-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of GET3 impair tail-anchored protein targeting? | GET3 knockout cell line |
| Does a point mutation in SEC61A1 alter translocation efficiency? | SEC61A1 point-mutation knock-in |
| Can EMC complex subunit tagging reveal dynamic interactions? | Tagged knock-in of EMC subunits |
| Does CFTR F508del affect ER exit? | CFTR F508del knock-in |
| Does SIGMAR1 overexpression protect against ER stress? | SIGMAR1 overexpression |
| Does SCAP-SREBP2 modulate inflammasome activation? | SCAP knockout and SREBP2 overexpression |
How to Study the post-translational protein targeting to endoplasmic reticulum membrane Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Ribo-seq | Translation efficiency and ribosome occupancy | Identify post-translationally targeted substrates |
| Proteomics | Protein interactions and complexes | Map chaperone-substrate networks |
| Live-cell imaging | Protein localization and dynamics | Track ER targeting in real time |
| CRISPR knockout screens | Gene essentiality and pathway regulators | Discover novel targeting factors |
| Co-immunoprecipitation | Protein-protein interactions | Validate Get3-substrate binding |
| In vitro translocation assays | Membrane insertion efficiency | Test Sec61 translocon function |
| Calcium imaging | ER-mitochondria Ca2+ signaling | Assess SIGMAR1 function |
| Lipidomics | Membrane composition | Study palmitoylation effects on ER membranes |
Ribosome profiling (Ribo-seq)
Ribo-seq measures translation efficiency and can identify mRNAs whose products are post-translationally targeted to the ER, revealing substrate specificity.
Proteomics and interactomics
Mass spectrometry-based proteomics identifies chaperone-substrate complexes and ER membrane insertion intermediates, as shown for Get3/TRC40 and EMC complexes.
Fluorescence imaging
Live-cell imaging of tagged tail-anchored proteins and ER markers visualizes targeting dynamics and membrane insertion in real time.
CRISPR screens
Genome-wide CRISPR knockout screens can uncover novel regulators of post-translational ER targeting and quality control.
How CRISPR Can Be Used to Study GO:0006620 post-translational protein targeting to endoplasmic reticulum membrane
Knockout
CRISPR knockout of GET3, GET1, GET2, or EMC subunits abolishes post-translational targeting, causing substrate accumulation and ER stress. These models are used to define essential components and compensatory pathways.
Point Mutation
Point mutations in SEC61A1 or GET3 can dissect ATPase activity, receptor binding, or translocation channel function without complete loss of protein. Such models reveal structure-function relationships.
Knock-in
Knock-in of tagged versions of EMC subunits or CFTR allows tracking of endogenous proteins and their trafficking from the ER. This approach preserves native regulation.
Overexpression
Overexpression of SIGMAR1 or SREBP2 can test gain-of-function effects on ER targeting, calcium signaling, and inflammasome activation. These models help identify therapeutic targets.
How EDITGENE Supports post-translational protein targeting to endoplasmic reticulum membrane Research
Researchers studying post-translational protein targeting to endoplasmic reticulum membrane-related genes often need to determine whether a candidate gene is causally involved in substrate delivery, membrane insertion, or disease progression. EDITGENE provides CRISPR-based cell models and screening services to accelerate this discovery.
Contact EDITGENE today to design your custom CRISPR model for post-translational protein targeting to endoplasmic reticulum membrane research.
Frequently Asked Questions About post-translational protein targeting to endoplasmic reticulum membrane
What is post-translational protein targeting to endoplasmic reticulum membrane?
It is the process by which fully synthesized proteins are delivered to the ER membrane after translation, using chaperones and the Get3/TRC40 pathway.
What genes are involved in post-translational protein targeting to the ER membrane?
Key genes include GET3, GET1, GET2, SEC61A1, SEC61B, SEC61G, and EMC1-EMC10.
How does post-translational targeting differ from co-translational targeting?
Post-translational targeting occurs after protein synthesis is complete and is SRP-independent, while co-translational targeting occurs during translation and requires SRP.
What is the role of the Get3/TRC40 chaperone?
Get3/TRC40 binds tail-anchored proteins, keeps them unfolded, and delivers them to the Get1/Get2 receptor on the ER membrane.
What diseases are linked to defects in this pathway?
Neurodegeneration, cystic fibrosis, and inflammatory/metabolic diseases have been linked to defects in ER targeting and quality control.
How can CRISPR be used to study this pathway?
CRISPR knockout, point mutation, knock-in, and overexpression models can dissect gene function and identify therapeutic targets.
What is the EMC complex?
The ER membrane protein complex (EMC) rectifies the topology of multipass membrane proteins and supports post-translational insertion.
What methods are used to study post-translational ER targeting?
Ribo-seq, proteomics, live-cell imaging, and CRISPR screens are commonly used.
Is the Sec61 translocon involved in post-translational targeting?
Yes, Sec61 mediates translocation of secretory proteins across the ER membrane after targeting.
What is the significance of tail-anchored proteins in this pathway?
Tail-anchored proteins rely on post-translational targeting for insertion into the ER membrane and regulate apoptosis, trafficking, and membrane fusion.
Conclusion
GO:0006620 encompasses a vital SRP-independent route for delivering fully synthesized proteins to the ER membrane, ensuring membrane protein biogenesis and ER homeostasis. Its machinery, from Get3/TRC40 to the EMC complex and Sec61 translocon, is linked to neurodegeneration, cystic fibrosis, and metabolic inflammation. CRISPR-based models and multi-omics approaches continue to illuminate this pathway, offering new therapeutic opportunities.
References
- 1. Itskanov S et al.. 2023. Mechanism of Protein Translocation by the Sec61 Translocon Complex.. Cold Spring Harb Perspect Biol 15(1) PMID: 35940906
- 2. Guo C et al.. 2018. Cholesterol Homeostatic Regulator SCAP-SREBP2 Integrates NLRP3 Inflammasome Activation and Cholesterol Biosynthetic Signaling in Macrophages.. Immunity 49(5):842-856.e7 PMID: 30366764
- 3. He Q et al.. 2023. Control of mitochondria-associated endoplasmic reticulum membranes by protein S-palmitoylation: Novel therapeutic targets for neurodegenerative diseases.. Ageing Res Rev 87:101920 PMID: 37004843
- 4. Hayashi T et al.. 2007. Sigma-1 receptor chaperones at the ER-mitochondrion interface regulate Ca(2+) signaling and cell survival.. Cell 131(3):596-610 PMID: 17981125
- 5. Johnson N et al.. 2013. Post-translational translocation into the endoplasmic reticulum.. Biochim Biophys Acta 1833(11):2403-9 PMID: 23266354
- 6. Wu H et al.. 2024. EMC rectifies the topology of multipass membrane proteins.. Nat Struct Mol Biol 31(1):32-41 PMID: 37957425
- 7. Farinha CM et al.. 2017. From the endoplasmic reticulum to the plasma membrane: mechanisms of CFTR folding and trafficking.. Cell Mol Life Sci 74(1):39-55 PMID: 27699454
- 8. Shan SO. 2019. Guiding tail-anchored membrane proteins to the endoplasmic reticulum in a chaperone cascade.. J Biol Chem 294(45):16577-16586 PMID: 31575659
