GO:0031204 post-translational protein targeting to membrane, translocation: Protein Transport Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0031204 describes the post-translational translocation of proteins through the ER membrane, a process that occurs after protein synthesis is complete.
• The Sec61 translocon is the central channel that mediates translocation of secretory and membrane proteins across the ER membrane.
• The post-translational translocation machinery includes the Sec61 complex, Sec62, Sec63, and BiP, which together facilitate protein transport.
• The EMC (ER membrane protein complex) plays a role in rectifying the topology of multipass membrane proteins during their insertion.
• Cross-talk exists between post-translational protein targeting and cytosolic quality control pathways, ensuring only properly folded proteins are translocated.
• Defects in post-translational translocation are linked to diseases such as cancer, neurodegeneration, and metabolic disorders [2,6].
Description
Post-translational protein targeting to membrane, translocation (GO:0031204) is a biological process in which proteins are transported across the endoplasmic reticulum (ER) membrane after their synthesis is complete. This pathway is essential for the delivery of secretory and membrane proteins to their correct destinations within the cell. Unlike co-translational translocation, where proteins are threaded into the ER as they are being synthesized, post-translational translocation allows fully synthesized proteins to be targeted and translocated, often requiring additional chaperones and targeting factors. The Sec61 translocon complex forms the core channel for this process, and its function is conserved from yeast to humans. Understanding this process is critical for researchers studying protein biogenesis, ER homeostasis, and related diseases. The fidelity of organellar protein targeting ensures that proteins reach the correct organelle, and disruptions can lead to cellular dysfunction. Moreover, the interplay between post-translational targeting and cytosolic quality control highlights the importance of this pathway in maintaining proteostasis.
post-translational protein targeting to membrane, translocation At A Glance
| GO ID | GO:0031204 |
|---|---|
| GO term | post-translational protein targeting to membrane, translocation |
| Ontology | biological_process |
| Synonym | posttranslational protein membrane targeting, translocation; posttranslational protein targeting to membrane, translocation; protein translocation during posttranslational protein targeting to membrane |
| Major function | Translocation of fully synthesized proteins across the ER membrane |
| Key components | Sec61 complex, Sec62, Sec63, BiP, EMC |
| Related pathways | Protein export, ER-associated degradation, unfolded protein response |
| Disease relevance | Cancer, neurodegeneration, metabolic disorders |
What Is GO:0031204?
GO:0031204 is defined as the process in which a protein translocates through the ER membrane posttranslationally. This means that after a protein is fully synthesized in the cytosol, it is targeted to and transported across the ER membrane. This process is distinct from co-translational translocation, where the protein is translocated while still being synthesized. The term encompasses the targeting of the protein to the membrane and its subsequent translocation through the membrane.
Why Is post-translational protein targeting to membrane, translocation Important in Cell Biology?
Post-translational protein targeting to membrane, translocation is crucial for maintaining cellular function because it ensures that proteins destined for the secretory pathway or for membrane insertion are correctly delivered. This process is particularly important for small proteins that are not efficiently targeted co-translationally. The Sec61 translocon is the central channel for this process, and its proper regulation is essential for ER homeostasis. Defects in this pathway can lead to the accumulation of misfolded proteins in the cytosol, triggering stress responses and contributing to diseases such as cancer and neurodegeneration [2,6]. Furthermore, the fidelity of organellar protein targeting is critical for cellular health, as mislocalized proteins can disrupt organelle function.
• Enables the translocation of fully synthesized proteins into the ER, a prerequisite for secretion and membrane insertion.
• Maintains ER homeostasis by ensuring proper protein folding and quality control.
• Plays a role in the unfolded protein response (UPR) by regulating the load of proteins entering the ER.
• Dysregulation is linked to cancer progression through altered secretion of growth factors and cytokines.
• Implicated in neurodegeneration due to impaired clearance of misfolded proteins.
• Affects metabolic disorders by influencing the secretion of hormones and enzymes.
• Provides targets for therapeutic intervention in diseases caused by protein misfolding.
• Cross-talk with cytosolic quality control ensures that only properly folded proteins are translocated.
• The EMC complex aids in the topogenesis of multipass membrane proteins, highlighting the complexity of the process.
• Understanding this pathway aids in the design of biologics and recombinant proteins.
What Happens During post-translational protein targeting to membrane, translocation?
Targeting of fully synthesized proteins to the ER membrane
In simple terms: After a protein is made, it needs to find its way to the ER membrane.
In post-translational translocation, proteins are fully synthesized in the cytosol before being targeted to the ER membrane. This targeting is mediated by signal sequences and requires cytosolic chaperones such as Hsp70 and Hsp40 to keep the protein in a translocation-competent state. The Sec62/Sec63 complex and BiP are involved in this process.
Recognition and binding to the Sec61 translocon
In simple terms: The protein binds to a channel called Sec61 on the ER membrane.
The Sec61 complex forms the protein-conducting channel. In post-translational translocation, the fully synthesized protein binds to the Sec61 complex, often with the help of the Sec62/Sec63 subcomplex. The structure of the post-translational translocation machinery has been resolved, revealing how Sec61 interacts with Sec62 and Sec63.
Translocation through the Sec61 channel
In simple terms: The protein passes through the Sec61 channel into the ER.
Once bound, the protein is threaded through the Sec61 channel. This process is driven by the binding of BiP (an Hsp70 chaperone in the ER) to the translocating chain, which acts as a ratchet to prevent backsliding. The Sec61 complex undergoes conformational changes to accommodate the polypeptide.
Folding and modification in the ER lumen
In simple terms: Inside the ER, the protein folds and gets modified.
After translocation, the protein is folded and modified in the ER lumen. Chaperones such as BiP and enzymes like protein disulfide isomerase (PDI) assist in folding. The EMC complex also plays a role in the biogenesis of multipass membrane proteins, ensuring correct topology.
Quality control and ER-associated degradation
In simple terms: Proteins that fail to fold are sent back for destruction.
Misfolded proteins are recognized by ER quality control and retrotranslocated to the cytosol for degradation by the proteasome, a process known as ER-associated degradation (ERAD). This cross-talk between post-translational targeting and cytosolic quality control ensures that only properly folded proteins proceed.
Key Genes Involved in GO:0031204 post-translational protein targeting to membrane, translocation
The following genes and proteins are key players in post-translational protein targeting to membrane, translocation.
| Gene | Major Role | Research Relevance |
|---|---|---|
| SEC61A1 | Core channel of the translocon | Mutations linked to diabetes and immunodeficiency |
| SEC61B | Accessory subunit of Sec61 complex | Regulates translocon function |
| SEC61G | Accessory subunit of Sec61 complex | Overexpressed in some cancers |
| SEC62 | Post-translational translocation component | Involved in ER stress response |
| SEC63 | Co-chaperone with BiP | Mutations cause polycystic liver disease |
| HSPA5 (BiP) | ER chaperone, drives translocation | Central to UPR and ER homeostasis |
| HSPA8 (Hsc70) | Cytosolic chaperone | Keeps proteins unfolded for translocation |
| DNAJC1 | Hsp40 co-chaperone | Assists in targeting |
| EMC1 | ER membrane protein complex subunit | Required for multipass membrane protein biogenesis |
| EMC2 | ER membrane protein complex subunit | Involved in topogenesis |
| EMC3 | ER membrane protein complex subunit | Mutations linked to neurodevelopmental disorders |
| EMC4 | ER membrane protein complex subunit | Stabilizes EMC complex |
| EMC6 | ER membrane protein complex subunit | Autophagy regulation |
| EMC7 | ER membrane protein complex subunit | Interacts with Sec61 |
| EMC10 | ER membrane protein complex subunit | Required for GPI-anchored protein biogenesis |
| SIGMAR1 | Sigma-1 receptor chaperone | Regulates ER-mitochondria Ca2+ signaling |
| SCAP | Cholesterol sensor | Integrates cholesterol synthesis with inflammasome |
How Is post-translational protein targeting to membrane, translocation Regulated?
The process of post-translational protein targeting to membrane, translocation is regulated at multiple levels. The unfolded protein response (UPR) senses the load of proteins in the ER and adjusts the expression of translocon components and chaperones. The sigma-1 receptor (SIGMAR1) at the ER-mitochondrion interface regulates Ca2+ signaling and cell survival, influencing ER function. Additionally, the SCAP-SREBP2 pathway integrates cholesterol biosynthetic signaling with inflammasome activation, which can affect ER membrane composition and translocation efficiency. Cytosolic quality control pathways also regulate the targeting step by ensuring that only properly folded proteins are presented for translocation.
post-translational protein targeting to membrane, translocation and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| SEC61A1 | Diabetes mellitus, immunodeficiency | Knockout in pancreatic beta cells |
| SEC63 | Polycystic liver disease | Knockout in hepatocytes |
| EMC1 | Neurodevelopmental disorder | Knockout in neurons |
| SIGMAR1 | ALS, Alzheimer's disease | Knockout in motor neurons |
| SCAP | Atherosclerosis, metabolic syndrome | Knockout in macrophages |
Cancer
Altered expression of Sec61 subunits and other translocon components has been observed in various cancers. For example, SEC61G is overexpressed in some tumors and is associated with poor prognosis. The increased demand for protein secretion in cancer cells may overload the translocon, making it a potential therapeutic target.
Neurodegeneration
Impaired ER function and protein misfolding are hallmarks of neurodegenerative diseases. The sigma-1 receptor (SIGMAR1) regulates ER-mitochondria signaling and cell survival, and its dysfunction has been implicated in amyotrophic lateral sclerosis (ALS) and Alzheimer's disease. Defects in post-translational translocation can lead to ER stress and neuronal death.
Metabolic disorders
Mutations in SEC61A1 cause a form of diabetes due to impaired insulin secretion. The SCAP-SREBP2 pathway links cholesterol metabolism to inflammasome activation, and its dysregulation contributes to atherosclerosis and metabolic syndrome.
Developmental disorders
Mutations in EMC subunits are associated with neurodevelopmental disorders, highlighting the importance of proper membrane protein biogenesis.
From post-translational protein targeting to membrane, translocation-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does SEC61A1 mutation affect insulin secretion? | Point mutation knock-in in INS-1 cells |
| Is EMC3 required for neuronal development? | Knockout in mouse embryonic stem cells |
| How does SEC62 overexpression affect ER stress? | Overexpression in HeLa cells |
| Does SIGMAR1 regulate ER-mitochondria Ca2+ signaling? | Knockout in SH-SY5Y cells |
| What is the role of SCAP in inflammasome activation? | Knockout in THP-1 macrophages |
| Can SEC61G be targeted for cancer therapy? | Knockout in cancer cell lines |
How to Study the post-translational protein targeting to membrane, translocation Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Ribo-seq | Translation efficiency and ribosome occupancy | Global analysis of protein synthesis |
| Proteomics | Protein abundance and interactions | Identifying translocon components |
| Live-cell imaging | Real-time translocation dynamics | Visualizing Sec61 channel activity |
| CRISPR knockout screens | Gene essentiality and synthetic lethality | Discovering novel translocation factors |
| Crosslinking mass spectrometry | Protein-protein interactions | Mapping Sec61-substrate contacts |
| In vitro translocation assay | Translocation efficiency | Biochemical dissection of mechanism |
| RNA-seq | Transcriptional changes | UPR target gene expression |
Proteomics and interactomics
Mass spectrometry-based proteomics can identify proteins associated with the translocon and quantify changes in translocation efficiency. Proximity labeling techniques such as BioID can map the interactome of Sec61 and its partners.
Imaging and live-cell analysis
Fluorescence microscopy and live-cell imaging allow visualization of protein translocation in real time. Tagged Sec61 subunits can be used to track ER dynamics and translocation events.
Genetic screens and CRISPR libraries
Genome-wide CRISPR knockout screens can identify genes required for post-translational translocation. Libraries targeting Sec61, Sec62, Sec63, and EMC subunits can reveal synthetic lethal interactions.
Biochemical assays
In vitro translocation assays using microsomes and radiolabeled proteins are classic methods to study post-translational translocation. These assays can be coupled with crosslinking to identify intermediates.
How CRISPR Can Be Used to Study GO:0031204 post-translational protein targeting to membrane, translocation
Knockout
CRISPR knockout of SEC61A1, SEC62, or SEC63 can be used to study their essential roles in post-translational translocation. Knockout cell lines often exhibit ER stress and impaired secretion.
Point Mutation
Point mutations in SEC61A1 identified in patients with diabetes can be introduced using CRISPR to model the disease and study the molecular defects.
Knock-in
Knock-in of tagged versions of Sec61 subunits (e.g., GFP or HA) allows for live-cell imaging and proteomic analysis of the translocon.
Overexpression
Overexpression of SEC61G or other subunits can mimic the increased translocation demand in cancer cells and help identify therapeutic vulnerabilities.
How EDITGENE Supports post-translational protein targeting to membrane, translocation Research
Researchers studying post-translational protein targeting to membrane, translocation-related genes often need to determine whether a candidate gene is causally involved in the pathway or is merely a bystander. EDITGENE provides a comprehensive suite of CRISPR services to enable precise genetic manipulation and functional studies.
Contact EDITGENE today to design your custom CRISPR model for post-translational protein targeting to membrane, translocation research.
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| SSR2 Knockout HEK293 Cell Line | EDJ-KQ5846 | Human | 6746 | Details Get a Quote |
| SSR3 Knockout HEK293 Cell Line | EDJ-KQ5847 | Human | 6747 | Details Get a Quote |
| SSR1 Knockout HEK293 Cell Line | EDJ-KQ5851 | Human | 6745 | Details Get a Quote |
| SEC61A2 Knockout HEK293 Cell Line | EDJ-KQ15214 | Human | 55176 | Details Get a Quote |
| SSR4 Knockout HEK293 Cell Line | EDJ-KQ15517 | Human | 6748 | Details Get a Quote |
| SEC61B Knockout HCT 116 Cell Line | EDJ-KQ18169 | Human | 10952 | Details Get a Quote |
| SEC61A2 Knockout A-549 Cell Line | EDJ-KQ45865 | Human | 55176 | Details Get a Quote |
| SEC61A2 Knockout HCT 116 Cell Line | EDJ-KQ45866 | Human | 55176 | Details Get a Quote |
| SEC61A2 Knockout HeLa Cell Line | EDJ-KQ45867 | Human | 55176 | Details Get a Quote |
| SSR2 Knockout A-549 Cell Line | EDJ-KQ29306 | Human | 6746 | Details Get a Quote |
| SSR2 Knockout HCT 116 Cell Line | EDJ-KQ29307 | Human | 6746 | Details Get a Quote |
| SSR2 Knockout HeLa Cell Line | EDJ-KQ29308 | Human | 6746 | Details Get a Quote |
| SSR3 Knockout A-549 Cell Line | EDJ-KQ29309 | Human | 6747 | Details Get a Quote |
| SSR3 Knockout HCT 116 Cell Line | EDJ-KQ29310 | Human | 6747 | Details Get a Quote |
| SSR3 Knockout HeLa Cell Line | EDJ-KQ29311 | Human | 6747 | Details Get a Quote |
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Frequently Asked Questions About post-translational protein targeting to membrane, translocation
What is GO:0031204?
GO:0031204 is the Gene Ontology term for post-translational protein targeting to membrane, translocation, the process by which fully synthesized proteins are transported across the ER membrane.
What genes are involved in post-translational protein targeting to membrane, translocation?
Key genes include SEC61A1, SEC61B, SEC61G, SEC62, SEC63, HSPA5 (BiP), and EMC subunits [1,4,8].
How does post-translational translocation differ from co-translational translocation?
In post-translational translocation, proteins are fully synthesized before translocation, whereas in co-translational translocation, proteins are translocated as they are being synthesized.
What is the role of the Sec61 complex?
The Sec61 complex forms the protein-conducting channel in the ER membrane through which proteins are translocated.
What diseases are associated with defects in post-translational translocation?
Defects are linked to diabetes, cancer, neurodegeneration, and developmental disorders [1,2,6,8].
How can CRISPR be used to study post-translational translocation?
CRISPR can create knockouts, point mutations, knock-ins, and overexpression models to dissect gene function in this pathway [1,4].
What is the EMC complex?
The ER membrane protein complex (EMC) is involved in the biogenesis of multipass membrane proteins and helps rectify their topology.
What is the unfolded protein response?
The UPR is a cellular stress response that regulates the expression of chaperones and translocon components to maintain ER homeostasis.
How is post-translational translocation regulated?
It is regulated by the UPR, cytosolic quality control, and signaling pathways such as the SCAP-SREBP2 pathway [1,2,7].
What methods are used to study post-translational translocation?
Methods include proteomics, live-cell imaging, CRISPR screens, and in vitro translocation assays [1,4,8].
Conclusion
Post-translational protein targeting to membrane, translocation (GO:0031204) is a fundamental cellular process that ensures the correct delivery of proteins to the ER. Its dysregulation is implicated in a range of diseases, making it an important area of research. Advances in CRISPR technology and omics approaches continue to unravel the molecular details of this pathway, offering potential therapeutic targets. EDITGENE provides the tools and services to facilitate these discoveries.
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
- 4. Wu X et al.. 2019. Structure of the post-translational protein translocation machinery of the ER membrane.. Nature 566(7742):136-139 PMID: 30644436
- 5. Song J et al.. 2022. Fidelity of organellar protein targeting.. Curr Opin Cell Biol 75:102071 PMID: 35306313
- 6. 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
- 7. Casson J et al.. 2016. On the road to nowhere: cross-talk between post-translational protein targeting and cytosolic quality control.. Biochem Soc Trans 44(3):796-801 PMID: 27284044
- 8. Wu H et al.. 2024. EMC rectifies the topology of multipass membrane proteins.. Nat Struct Mol Biol 31(1):32-41 PMID: 37957425
