GO:0006617 SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition: Mechanism, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0006617 describes the step in which the signal recognition particle (SRP) binds a nascent signal peptide, pauses translation elongation, and commits the ribosome-nascent chain complex to cotranslational membrane targeting.
• The reaction is conserved from bacteria to humans, with the bacterial SRP-FtsY complex captured in a closed state by cryo-EM.
• Signal sequence recognition is not absolutely required for SRP-SR complex formation at the membrane, revealing alternative targeting routes within the SRP cycle.
• SRP can also mediate post-translational targeting in eukaryotes, expanding the functional repertoire of signal sequence recognition beyond the canonical cotranslational pathway.
• Extended or atypical signal peptides, such as those on bacterial virulence factors, can be recognized by SRP and routed to the membrane.
• Small membrane proteins and tail-anchored proteins can use SRP-dependent and SRP-independent routes, and cotranslational and post-translational targeting can cooperate in topogenesis.
Description
GO:0006617, SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition, is the biological process in which the signal recognition particle (SRP) recognizes a hydrophobic signal peptide emerging from the ribosomal exit tunnel, causing elongation to pause and initiating cotranslational delivery of the ribosome-nascent chain complex to the membrane. This step is the decisive commitment point that distinguishes secretory and membrane proteins from cytosolic polypeptides and is therefore central to proteostasis, organelle biogenesis, and cell-surface proteome composition. Structural and biochemical work has defined the ribosome-SRP-FtsY cotranslational targeting complex in a closed state, providing a molecular framework for how signal sequence recognition is coupled to GTP-dependent checkpoint control. In parallel, studies have shown that SRP can also support post-translational targeting in eukaryotes and that signal sequence-independent SRP-SR complex formation can occur at the membrane, indicating that signal sequence recognition is embedded in a flexible targeting network rather than a single linear route. For researchers, GO:0006617 is a tractable node for interrogating how cells sort the secretome and membrane proteome, and for dissecting how defects in this step contribute to disease and to the biogenesis of small and tail-anchored membrane proteins.
SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition At A Glance
| GO ID | GO:0006617 |
|---|---|
| GO term | SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition |
| Ontology | biological_process |
| Synonym | signal sequence recognition during SRP-dependent cotranslational protein targeting to membrane; SRP-dependent cotranslational membrane targeting, signal sequence recognition; SRP-dependent cotranslational protein-membrane targeting, signal sequence recognition |
| Major function | SRP binding to the nascent signal peptide, pausing elongation and committing the ribosome-nascent chain complex to cotranslational membrane targeting |
| Cellular context | Ribosome-nascent chain complex at the endoplasmic reticulum membrane in eukaryotes and the plasma membrane in bacteria |
| Key molecular players | SRP, SRP receptor (SR), FtsY in bacteria, and the translating ribosome |
| Pathway position | Early, signal sequence recognition step of SRP-dependent cotranslational protein targeting to membrane |
What Is GO:0006617?
In our own words, GO:0006617 is the process in which SRP binds to the signal peptide of a nascent protein, causing protein elongation to pause, during cotranslational membrane targeting. It is the signal sequence recognition step of SRP-dependent cotranslational protein targeting to membrane, and it is defined in QuickGO as the process in which SRP binds to the signal peptide in a nascent protein, causing protein elongation to pause, during cotranslational membrane targeting.
Why Is SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition Important in Cell Biology?
GO:0006617 matters because it is the point at which the fate of a nascent polypeptide is decided: whether it will be delivered to the membrane or remain cytosolic. Structural analysis of the ribosome-SRP-FtsY cotranslational targeting complex in the closed state has revealed how signal sequence recognition is coupled to GTP-dependent checkpoint control, making this step a paradigm for studying molecular recognition and fidelity. The same step is now understood to operate within a broader targeting network that includes post-translational SRP-dependent targeting in eukaryotes and signal sequence-independent SRP-SR complex formation at the membrane. Because small membrane proteins and tail-anchored proteins can use SRP-dependent and SRP-independent routes, and because cotranslational and post-translational targeting can cooperate in topogenesis, signal sequence recognition is relevant to essentially every membrane and secretory protein biogenesis question. Defects in this step are therefore expected to affect cell-surface signaling, secretion, and organelle function, and to intersect with disease mechanisms that involve membrane protein mislocalization.
• Defines the commitment step for secretory and membrane protein biogenesis.
• Provides a structural paradigm for signal peptide recognition and GTP-dependent checkpoint control.
• Explains how SRP can function in post-translational targeting in eukaryotes.
• Reveals signal sequence-independent SRP-SR complex formation at the membrane, expanding the SRP cycle.
• Underpins biogenesis of small membrane proteins and tail-anchored proteins.
• Shows that cotranslational and post-translational targeting can cooperate in topogenesis.
• Relevant to bacterial virulence factor targeting via extended signal peptides.
• Provides a framework for studying membrane proteome composition and secretion.
• Links to disease through mislocalization of membrane and secretory proteins.
• Enables CRISPR-based dissection of SRP pathway components in human cells.
What Happens During SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition?
Signal peptide emergence and SRP recruitment
In simple terms: As a new protein starts to come out of the ribosome, a hydrophobic tag called a signal peptide is exposed, and SRP grabs it.
During translation, the hydrophobic signal peptide emerges from the ribosomal exit tunnel and is recognized by SRP, which binds the ribosome-nascent chain complex. This recognition event is the defining feature of GO:0006617 and is required for the subsequent pause in elongation. Structural studies of the ribosome-SRP-FtsY cotranslational targeting complex in the closed state have visualized how SRP engages the signal peptide and the ribosome to form a stable targeting-competent complex.
Elongation arrest and checkpoint control
In simple terms: Once SRP binds, the ribosome slows down or stops making the protein, giving the cell time to deliver it to the membrane.
SRP binding to the signal peptide causes protein elongation to pause, which is a hallmark of GO:0006617. This elongation arrest is coupled to GTP-dependent checkpoint control, as revealed by the closed-state structure of the ribosome-SRP-FtsY complex. The pause ensures that the nascent chain is not prematurely released into the cytosol and that targeting occurs cotranslationally.
SRP-SR interaction and membrane delivery
In simple terms: The SRP-carrying ribosome docks onto a receptor at the membrane, handing the new protein over to the translocation machinery.
After signal sequence recognition, the SRP-ribosome-nascent chain complex engages the SRP receptor at the membrane. Signal sequence-independent SRP-SR complex formation at the membrane suggests an alternative targeting pathway within the SRP cycle, indicating that SRP-SR interaction can occur even without a canonical signal peptide. In eukaryotes, SRP can also mediate post-translational targeting, showing that the SRP cycle is not strictly limited to cotranslational delivery.
Handover and integration into the broader targeting network
In simple terms: The new protein is handed off to the membrane insertion machinery, and different targeting routes can cooperate depending on the protein.
Molecular mechanism studies of cargo recognition and handover by the mammalian SRP have defined how the signal peptide is transferred from SRP to the translocation channel. Cotranslational targeting and posttranslational translocation can cooperate in Spc3 topogenesis, demonstrating that signal sequence recognition operates within a flexible network. Small membrane proteins can be inserted posttranslationally by the bacterial SRP, and tail-anchored proteins use dedicated membrane insertion pathways, further illustrating the diversity of routes that intersect with GO:0006617.
Atypical signal sequences and virulence factors
In simple terms: Some proteins have unusual signal tags, and SRP can still recognize them to send bacterial virulence factors to the membrane.
Membrane targeting of a bacterial virulence factor harbouring an extended signal peptide shows that SRP can recognize non-canonical signal sequences. This expands the substrate range of GO:0006617 beyond classical hydrophobic signal peptides and links signal sequence recognition to bacterial pathogenesis. Together with evidence for signal sequence-independent SRP-SR complex formation, these findings indicate that signal sequence recognition is a versatile recognition step rather than a single rigid mechanism.
Key Genes Involved in GO:0006617 SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition
The genes and proteins below are the core machinery and regulatory factors that carry out or modulate signal sequence recognition during SRP-dependent cotranslational protein targeting to membrane.
| Gene | Major Role | Research Relevance |
|---|---|---|
| SRP54 | Signal peptide binding subunit of SRP | Central to signal sequence recognition and elongation arrest |
| SRP9 | SRP Alu domain component | Contributes to elongation arrest during targeting |
| SRP14 | SRP Alu domain component | Part of the SRP complex that pauses translation |
| SRP19 | SRP S domain assembly factor | Required for SRP RNA and SRP54 assembly |
| SRP68 | SRP S domain component | Structural role in SRP-mediated targeting |
| SRP72 | SRP S domain component | Structural role in SRP-mediated targeting |
| SRPR | Eukaryotic SRP receptor alpha subunit | Docks SRP at the ER membrane |
| SRPRB | Eukaryotic SRP receptor beta subunit | Membrane anchor and GTPase regulation |
| FtsY | Bacterial SRP receptor | Forms closed-state complex with SRP and ribosome |
| FFH | Bacterial SRP protein component | Signal peptide recognition in bacteria |
| SEC61A1 | ER translocon subunit | Receives nascent chains after SRP handover |
| SEC61B | ER translocon subunit | Part of the protein-conducting channel |
| SEC61G | ER translocon subunit | Part of the protein-conducting channel |
| GET3 | Tail-anchored protein targeting factor | SRP-independent route for membrane proteins |
| WRB | Tail-anchored protein receptor | Membrane insertion of tail-anchored proteins |
| CAMLG | Tail-anchored protein receptor | Membrane insertion of tail-anchored proteins |
| SPC3 | Small membrane protein model substrate | Cotranslational and posttranslational cooperation |
How Is SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition Regulated?
Signal sequence recognition during SRP-dependent cotranslational protein targeting to membrane is regulated at multiple levels. The closed-state ribosome-SRP-FtsY complex reveals GTP-dependent checkpoint control that couples signal peptide recognition to elongation arrest and handover. Signal sequence-independent SRP-SR complex formation at the membrane indicates that the SRP cycle can be modulated by membrane-localized interactions, providing an alternative regulatory route. In eukaryotes, SRP can mediate post-translational targeting, suggesting that the timing and mode of signal sequence recognition are regulated by the availability of SRP and its receptor. Cargo recognition and handover by the mammalian SRP are also regulated by the structural state of the SRP and the nascent chain. Finally, cooperation between cotranslational and posttranslational targeting in Spc3 topogenesis shows that the pathway is tuned by substrate features and membrane factors.
SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| SRP54 | Membrane protein mislocalization and secretory defects | Knockout and point-mutation cell models |
| SRPR | Defective ER targeting and secretion | Knock-in of patient variants |
| SEC61A1 | Translocon dysfunction and protein biogenesis disorders | Knockout and tagged knock-in |
| GET3 | Tail-anchored protein mislocalization | Overexpression and knockout |
| FFH | Bacterial virulence and membrane targeting | Bacterial knockout and point mutation |
Membrane protein mislocalization and disease
Defects in signal sequence recognition can lead to mislocalization of membrane and secretory proteins, which is a common theme in diseases affecting cell-surface signaling and secretion. Because small membrane proteins and tail-anchored proteins depend on SRP-dependent and SRP-independent routes, disruption of these pathways can alter membrane proteome composition and organelle function. Cotranslational and posttranslational targeting cooperation in Spc3 topogenesis further suggests that disease-associated mutations in membrane proteins may shift the balance between targeting routes.
Bacterial pathogenesis and virulence factor targeting
Bacterial virulence factors with extended signal peptides can be targeted to the membrane via SRP, linking signal sequence recognition to pathogenesis. The bacterial SRP-FtsY system is structurally conserved and has been captured in a closed state, making it a potential target for antibacterial strategies. Posttranslational insertion of small membrane proteins by the bacterial SRP further highlights the importance of this pathway in bacterial physiology.
Ribosomopathies and translational stress
Elongation arrest during signal sequence recognition is a translational checkpoint, and its dysregulation could contribute to ribosomopathy-like phenotypes. The closed-state structure of the ribosome-SRP-FtsY complex provides a framework for understanding how mutations in SRP or ribosomal components might affect this checkpoint. Mammalian SRP cargo recognition and handover mechanisms are also relevant to translational stress responses.
From SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of SRP54 impair signal sequence recognition? | SRP54 knockout cell line |
| Does a disease variant alter SRP-SR interaction? | Point-mutation knock-in of SRPR or SRPRB |
| Can a tagged SRP component be tracked in live cells? | Tagged knock-in of SRP54 or SRP68 |
| Does overexpression of SRP rescue targeting defects? | Overexpression of SRP subunits |
| How do small membrane proteins use SRP routes? | Knockout of GET3 and SRP components |
| Can cotranslational and posttranslational targeting cooperate? | Spc3 topogenesis reporter with knockout backgrounds |
How to Study the SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Ribo-seq | Ribosome occupancy and elongation pausing | Detect elongation arrest during signal sequence recognition |
| Cryo-EM | Three-dimensional structure of targeting complexes | Visualize ribosome-SRP-FtsY closed state |
| Proteomics | Membrane and secreted protein abundance | Quantify mislocalization after SRP perturbation |
| Membrane fractionation | Subcellular distribution of proteins | Assess targeting defects |
| Fluorescence microscopy | Localization of SRP and nascent chains | Track targeting in live cells |
| Single-molecule FRET | Dynamic interactions of SRP and SR | Study signal sequence-independent complex formation |
| GTPase assays | GTP hydrolysis by SRP and SR | Measure checkpoint control |
| CRISPR knockout screens | Gene dependency of targeting pathway | Identify modifiers of signal sequence recognition |
Ribosome profiling (Ribo-seq)
Ribo-seq measures ribosome occupancy and elongation pausing, making it ideal to detect the elongation arrest caused by signal sequence recognition. By comparing wild-type and SRP-mutant cells, researchers can quantify how loss of signal sequence recognition alters ribosome footprints on secretory and membrane protein mRNAs.
Structural biology (cryo-EM and X-ray crystallography)
Cryo-EM has captured the ribosome-SRP-FtsY cotranslational targeting complex in the closed state, revealing the molecular details of signal sequence recognition and checkpoint control. Structural approaches are essential to map how SRP binds the signal peptide and how SRP-SR complex formation occurs at the membrane.
Proteomics and membrane fractionation
Proteomics combined with membrane fractionation can quantify how loss of signal sequence recognition affects the membrane proteome and secretion. This approach is particularly useful for small membrane proteins and tail-anchored proteins that use SRP-dependent and SRP-independent routes.
Fluorescence imaging and single-molecule assays
Fluorescence imaging and single-molecule assays can track SRP-ribosome-nascent chain complexes and their delivery to the membrane in real time. These methods help distinguish cotranslational from post-translational targeting and reveal signal sequence-independent SRP-SR complex formation.
How CRISPR Can Be Used to Study GO:0006617 SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition
Knockout
CRISPR knockout of SRP subunits, SRP receptor components, or translocon subunits can be used to test whether signal sequence recognition is required for membrane protein biogenesis and secretion. Knockout cell lines also allow Ribo-seq-based measurement of elongation arrest defects.
Point Mutation
Point mutations in SRP54, SRPR, or FtsY can be introduced to dissect the GTP-dependent checkpoint and signal peptide binding interfaces identified in the closed-state structure. Such models are useful for testing disease-associated variants that alter signal sequence recognition.
Knock-in
Tagged knock-in of SRP components or SRP receptor subunits enables live-cell imaging and biochemical purification of targeting complexes. Knock-in of disease variants can reveal how specific mutations affect signal sequence recognition and membrane delivery.
Overexpression
Overexpression of SRP subunits or SRP receptor can rescue targeting defects or amplify signal sequence recognition for biochemical assays. Overexpression models are also useful for studying post-translational SRP-dependent targeting in eukaryotes.
How EDITGENE Supports SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition Research
Researchers studying SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition-related genes often need to determine whether a candidate gene is causally involved in signal peptide recognition, elongation arrest, or membrane delivery. EDITGENE provides the full suite of CRISPR cell model services to enable that causal testing in physiologically relevant systems.
Contact EDITGENE today to design your custom CRISPR model for SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition research.
Frequently Asked Questions About SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition
What is GO:0006617?
GO:0006617 is the biological process in which SRP binds to the signal peptide in a nascent protein, causing protein elongation to pause, during cotranslational membrane targeting.
What is SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition?
It is the signal sequence recognition step in which SRP recognizes a nascent signal peptide, pauses translation, and commits the ribosome-nascent chain complex to cotranslational membrane targeting.
What genes are involved in SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition?
Key genes include SRP54, SRP9, SRP14, SRP19, SRP68, SRP72, SRPR, SRPRB, FtsY, FFH, SEC61A1, SEC61B, SEC61G, GET3, WRB, CAMLG, and SPC3.
How does SRP recognize a signal peptide?
SRP binds the hydrophobic signal peptide as it emerges from the ribosomal exit tunnel, forming a targeting-competent complex that pauses elongation.
Is signal sequence recognition always required for SRP-SR complex formation?
No; signal sequence-independent SRP-SR complex formation at the membrane suggests an alternative targeting pathway within the SRP cycle.
Can SRP mediate post-translational targeting in eukaryotes?
Yes, SRP mediates post-translational targeting in eukaryotes, expanding its role beyond cotranslational delivery.
What is the role of FtsY in signal sequence recognition?
FtsY is the bacterial SRP receptor that forms a closed-state complex with SRP and the ribosome during cotranslational targeting.
How do small membrane proteins use SRP?
Small membrane proteins can be inserted posttranslationally by the bacterial SRP, and tail-anchored proteins use dedicated SRP-independent pathways.
Can cotranslational and posttranslational targeting cooperate?
Yes, cotranslational targeting and posttranslational translocation can cooperate in Spc3 topogenesis.
How can CRISPR help study GO:0006617?
CRISPR knockout, point mutation, knock-in, and overexpression models allow causal testing of SRP pathway genes and their role in signal sequence recognition.
Conclusion
GO:0006617, SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition, is a central and structurally well-defined step in membrane and secretory protein biogenesis. It couples signal peptide recognition to elongation arrest and membrane delivery, and it operates within a flexible network that includes post-translational targeting and signal sequence-independent SRP-SR complex formation. Because small membrane proteins, tail-anchored proteins, and bacterial virulence factors all intersect with this pathway, signal sequence recognition is relevant to diverse biological questions. CRISPR-based cell models from EDITGENE provide a direct route to test how individual genes contribute to this process and to disease-relevant mislocalization phenotypes.
References
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- 2. von Loeffelholz O et al.. 2015. Ribosome-SRP-FtsY cotranslational targeting complex in the closed state.. Proc Natl Acad Sci U S A 112(13):3943-8 PMID: 25775537
- 3. Jung SJ et al.. 2021. Cotranslational Targeting and Posttranslational Translocation can Cooperate in Spc3 Topogenesis.. J Mol Biol 433(18):167109 PMID: 34153287
- 4. Steinberg R et al.. 2020. Posttranslational insertion of small membrane proteins by the bacterial signal recognition particle.. PLoS Biol 18(9):e3000874 PMID: 32997663
- 5. Braig D et al.. 2011. Signal sequence-independent SRP-SR complex formation at the membrane suggests an alternative targeting pathway within the SRP cycle.. Mol Biol Cell 22(13):2309-23 PMID: 21551068
- 6. Abell BM et al.. 2004. Signal recognition particle mediates post-translational targeting in eukaryotes.. EMBO J 23(14):2755-64 PMID: 15229647
- 7. Jomaa A et al.. 2021. Molecular mechanism of cargo recognition and handover by the mammalian signal recognition particle.. Cell Rep 36(2):109350 PMID: 34260909
- 8. Chevalier N et al.. 2004. Membrane targeting of a bacterial virulence factor harbouring an extended signal peptide.. J Mol Microbiol Biotechnol 8(1):7-18 PMID: 15741736
