GO:0022624 proteasome accessory complex: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0022624 (proteasome accessory complex) is a cellular_component term describing a protein complex that caps one or both ends of the proteasome core complex and regulates entry into, or exit from, the proteasome core complex.
• The proteasome accessory complex includes the 19S regulatory particle (PA700) in eukaryotes, which recognizes ubiquitinated substrates, unfolds them, and translocates them into the 20S core particle.
• Accessory proteins such as HECT ubiquitin ligases and p97/VCP with RAD23A/B adaptors modulate substrate delivery and degradation decisions at the proteasome.
• Viral proteins, including HIV Vpx and SARS-CoV-2 ORF9b, hijack proteasome accessory complexes to evade host immunity or regulate viral replication.
• Dysregulation of proteasome accessory complexes is linked to cancer, neurodegeneration, and viral pathogenesis, making them attractive therapeutic targets.
• CRISPR knockout, point mutation, knock-in, and overexpression models enable precise interrogation of proteasome accessory complex components in disease and drug discovery.
Description
The proteasome accessory complex (GO:0022624) is a conserved cellular machine that caps the proteasome core complex and governs substrate entry and exit, thereby controlling protein degradation specificity. In eukaryotes, the best-characterized accessory complex is the 19S regulatory particle, which binds ubiquitinated substrates, removes ubiquitin chains, unfolds polypeptides, and feeds them into the 20S catalytic core. This regulatory layer is essential for maintaining proteostasis, regulating cell cycle progression, and mounting immune responses. Beyond the canonical 19S particle, accessory proteins such as HECT ubiquitin ligases and p97/VCP with RAD23A/B adaptors fine-tune substrate selection and degradation efficiency. Recent studies show that viruses, including HIV and SARS-CoV-2, exploit these accessory complexes to manipulate host protein turnover and evade immunity. Understanding the composition, assembly, and regulation of the proteasome accessory complex is therefore critical for basic cell biology and for developing targeted therapies in cancer, neurodegeneration, and infectious disease.
proteasome accessory complex At A Glance
| GO ID | GO:0022624 |
|---|---|
| GO term | proteasome accessory complex |
| Ontology | cellular_component |
| Synonym | None |
| Major function | Caps the proteasome core complex and regulates entry into or exit from the core |
| Cellular location | Cytoplasm and nucleus, associated with the 20S proteasome core |
| Key components | 19S regulatory particle subunits (e.g., PSMD1-14, PSMC1-6), PA28/11S regulators, and accessory proteins such as HECT ligases and p97/VCP |
| Associated processes | Ubiquitin-dependent protein degradation, proteostasis, antigen processing, cell cycle control |
| Disease relevance | Cancer, neurodegeneration, viral infections (HIV, SARS-CoV-2) |
What Is GO:0022624?
According to the Gene Ontology, GO:0022624 (proteasome accessory complex) is defined as a protein complex that caps one or both ends of the proteasome core complex and regulates entry into, or exit from, the proteasome core complex. This definition emphasizes the accessory complex's structural position (capping the core) and its regulatory role in gating substrate access to the proteasome's catalytic chamber. In practice, the term encompasses the 19S regulatory particle (PA700) in eukaryotes, as well as related accessory factors that associate with the 20S core to modulate degradation.
Why Is proteasome accessory complex Important in Cell Biology?
The proteasome accessory complex is a central gatekeeper of protein degradation, determining which proteins are destroyed and when. By capping the 20S core and regulating substrate entry, it ensures that only properly tagged and unfolded proteins are degraded, thereby protecting cells from toxic protein aggregation and maintaining signaling fidelity. Its dysfunction contributes to cancer progression, neurodegenerative disorders, and viral pathogenesis, and it is a validated target for drugs such as bortezomib and carfilzomib. Studying this complex is therefore essential for understanding proteostasis and for developing next-generation therapeutics.
• Controls ubiquitin-dependent protein degradation, a fundamental process in all eukaryotes.
• Regulates cell cycle progression by degrading cyclins and CDK inhibitors.
• Participates in antigen processing for MHC class I presentation.
• Is hijacked by viruses such as HIV and SARS-CoV-2 to manipulate host immunity.
• Its dysfunction is linked to cancer, neurodegeneration, and inflammatory diseases.
• Serves as a target for proteasome inhibitors used in multiple myeloma and other cancers.
• Accessory proteins like HECT ligases and p97/VCP add layers of substrate specificity.
• CRISPR screens can identify novel accessory complex components and modifiers.
• Its assembly and regulation are potential therapeutic entry points for antiviral and anticancer strategies.
What Happens During proteasome accessory complex?
Substrate Recognition and Binding
In simple terms: The accessory complex grabs proteins that are tagged for destruction.
The 19S regulatory particle, a major proteasome accessory complex, recognizes polyubiquitinated substrates through receptors such as RPN10 and RPN13. These receptors bind ubiquitin chains and initiate substrate engagement, while deubiquitinating enzymes (e.g., RPN11) remove the ubiquitin tag to allow substrate entry. Accessory proteins like RAD23A/B can shuttle ubiquitinated proteins to the proteasome, as shown for p97-mediated degradation.
Unfolding and Translocation
In simple terms: The complex unfolds the tagged protein and pushes it into the core for destruction.
Once bound, the 19S particle uses ATPases (PSMC1-6) to unfold the substrate and translocate it into the 20S core particle. This process is ATP-dependent and requires a narrow channel that only allows unfolded polypeptides to pass. The accessory complex thus acts as a molecular gate, preventing uncontrolled access to the catalytic chamber.
Regulation by Accessory Proteins
In simple terms: Other proteins can attach to the complex and change what gets degraded.
HECT ubiquitin ligases can act as accessory proteins of the plant proteasome, adding ubiquitin chains to substrates and modulating degradation. Similarly, p97/VCP with RAD23A/B adaptors determines whether specific substrates are degraded by the proteasome in human cells. These accessory factors provide additional layers of specificity and regulation.
Viral Hijacking of Accessory Complexes
In simple terms: Viruses can use the complex to destroy host defense proteins.
HIV-2 Vpx hijacks a Cullin 5-based complex to degrade SAMHD1, enhancing viral infection. SARS-CoV-2 ORF9b stability is modulated by a Cullin 5-based complex, which serves as an essential regulator of viral replication. These examples illustrate how viruses exploit proteasome accessory complexes for immune evasion.
Key Genes Involved in GO:0022624 proteasome accessory complex
The following genes encode core components and accessory factors of the proteasome accessory complex (GO:0022624) and are frequently studied in degradation, disease, and drug discovery research.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PSMD1 | 19S regulatory particle base subunit | Knockout reduces proteasome activity; cancer target |
| PSMD2 | 19S base subunit, interacts with ubiquitin receptors | Mutations affect substrate recognition |
| PSMD4 | Ubiquitin receptor RPN10 | Mediates polyubiquitin chain binding |
| PSMD7 | 19S lid subunit, deubiquitination | Regulates substrate processing |
| PSMD11 | 19S lid subunit | Linked to stem cell pluripotency |
| PSMD14 | Deubiquitinating enzyme RPN11 | Essential for substrate entry |
| PSMC1 | ATPase subunit of 19S base | Required for unfolding and translocation |
| PSMC2 | ATPase subunit | Mutations impair degradation |
| PSMC3 | ATPase subunit | Interacts with substrate receptors |
| PSMC4 | ATPase subunit | Regulates gate opening |
| PSMC5 | ATPase subunit | Modulates proteasome assembly |
| PSMC6 | ATPase subunit | ATP-dependent substrate processing |
| RAD23A | Ubiquitin-like adaptor | Shuttles substrates to proteasome with p97 |
| RAD23B | Ubiquitin-like adaptor | Works with RAD23A in degradation |
| VCP (p97) | AAA+ ATPase | Extracts substrates for proteasomal degradation |
| CUL5 | Cullin 5 scaffold | Forms E3 ligase complex targeting viral proteins |
| UBE3A | HECT ubiquitin ligase | Accessory protein in plant proteasome |
How Is proteasome accessory complex Regulated?
The proteasome accessory complex is regulated at multiple levels, including ATP availability, post-translational modifications of 19S subunits, and interaction with accessory proteins such as p97/VCP and RAD23A/B. Phosphorylation of 19S subunits can modulate proteasome activity in response to cellular stress. Additionally, viral proteins like HIV Vpx and SARS-CoV-2 ORF9b can hijack Cullin 5-based complexes to redirect degradation for immune evasion. HECT ubiquitin ligases also act as accessory proteins that regulate substrate selection in plants.
proteasome accessory complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| PSMD1 | Multiple myeloma, cancer | Knockout in myeloma cell lines; drug sensitivity assays |
| VCP (p97) | IBMPFD, ALS | Knock-in of patient mutations in iPSCs; proteostasis assays |
| CUL5 | HIV-2, SARS-CoV-2 | Knockout in HEK293T; viral replication assays |
| RAD23A/B | Neurodegeneration | Double knockout in neurons; aggregate clearance assays |
| UBE3A | Plant immunity | Knockout in Arabidopsis; pathogen response |
Cancer
Proteasome accessory complex components are overexpressed in multiple myeloma and other cancers, and proteasome inhibitors such as bortezomib target the 20S core but rely on accessory complex function for substrate processing. Dysregulation of 19S subunits can promote tumor survival by enhancing degradation of pro-apoptotic factors.
Neurodegeneration
Impaired proteasome accessory complex function contributes to the accumulation of toxic protein aggregates in neurodegenerative diseases such as Alzheimer's and Parkinson's. p97/VCP mutations are linked to IBMPFD and ALS, highlighting the importance of accessory factors in neuronal proteostasis.
Viral Infections
HIV-2 Vpx hijacks a Cullin 5-based complex to degrade SAMHD1, and SARS-CoV-2 ORF9b stability is regulated by a similar complex, demonstrating how viruses exploit proteasome accessory machinery for replication and immune evasion.
From proteasome accessory complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does PSMD1 loss impair proteasome activity? | CRISPR knockout in HEK293T |
| How does VCP mutation affect substrate degradation? | Point mutation knock-in in iPSCs |
| Can tagged PSMD4 track proteasome localization? | Knock-in of GFP-PSMD4 |
| Does CUL5 overexpression enhance viral replication? | Overexpression in A549 cells |
| Which accessory genes are essential for cancer growth? | Genome-wide CRISPR library screening |
| How does RAD23A/B double knockout affect proteostasis? | Double knockout in mouse embryonic fibroblasts |
How to Study the proteasome accessory complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Affinity purification + MS | Protein composition of accessory complex | Identifying novel subunits |
| CRISPR knockout screens | Gene essentiality and modifiers | Cancer drug resistance |
| Live-cell imaging | Localization and dynamics | Proteasome assembly |
| In vitro degradation assay | ATP-dependent proteolysis | Mechanistic studies |
| Ubiquitin chain profiling | Substrate ubiquitination status | Accessory ligase activity |
| RNA-seq | Transcriptional changes upon knockout | Pathway analysis |
| Proximity labeling (BioID) | Interactome of accessory proteins | Mapping dynamic complexes |
Proteomics and Mass Spectrometry
Affinity purification of the 19S regulatory particle followed by mass spectrometry can identify accessory complex components and their interactors. Quantitative proteomics can measure changes in substrate degradation upon knockout of accessory genes.
CRISPR Screening
Genome-wide CRISPR knockout screens can identify genes that modify proteasome accessory complex function or drug sensitivity. These screens are powerful for discovering novel regulators and therapeutic targets.
Imaging and Localization
Fluorescent tagging of 19S subunits (e.g., GFP-PSMD4) enables live-cell imaging of proteasome accessory complex localization and dynamics. Super-resolution microscopy can reveal capping of the 20S core.
Biochemical Assays
In vitro degradation assays using purified 20S and 19S particles can measure ATP-dependent substrate unfolding and translocation. Deubiquitination assays can assess RPN11 activity.
How CRISPR Can Be Used to Study GO:0022624 proteasome accessory complex
Knockout
CRISPR knockout of PSMD1 or PSMC1 in cell lines abolishes 19S function, leading to impaired degradation of ubiquitinated substrates and accumulation of aggregates. Knockout of CUL5 reduces HIV-2 and SARS-CoV-2 replication, validating its role in viral hijacking.
Point Mutation
Point mutations in VCP (e.g., R155H) linked to IBMPFD can be introduced via CRISPR to study dominant-negative effects on proteasome accessory complex function. Similarly, mutations in PSMD2 can reveal residues critical for substrate recognition.
Knock-in
Knock-in of GFP or HA tags at endogenous PSMD4 or PSMD14 loci allows tracking of accessory complex assembly and dynamics in real time. Knock-in of patient mutations in RAD23B can model neurodegeneration.
Overexpression
Overexpression of HECT ubiquitin ligases or CUL5 can enhance substrate degradation or viral replication, providing gain-of-function models to study accessory complex regulation. Overexpression of PSMD11 increases proteasome activity and stemness.
How EDITGENE Supports proteasome accessory complex Research
Researchers studying proteasome accessory complex-related genes often need to determine whether a candidate gene is causally involved in substrate degradation, disease progression, or viral replication. EDITGENE provides end-to-end CRISPR services to generate precisely engineered cell models for such functional studies.
Contact EDITGENE today to design your custom CRISPR model for proteasome accessory complex research.
Frequently Asked Questions About proteasome accessory complex
What is the proteasome accessory complex?
The proteasome accessory complex (GO:0022624) is a protein complex that caps the proteasome core complex and regulates entry into or exit from the core, controlling protein degradation.
What genes are involved in the proteasome accessory complex?
Key genes include PSMD1-14, PSMC1-6 (19S subunits), RAD23A/B, VCP (p97), CUL5, and HECT ubiquitin ligases such as UBE3A.
What is the function of GO:0022624?
It regulates substrate recognition, unfolding, and translocation into the 20S core, thereby controlling ubiquitin-dependent protein degradation.
How is the proteasome accessory complex regulated?
It is regulated by ATP, post-translational modifications, and accessory proteins like p97/VCP and RAD23A/B, as well as viral hijacking.
Which diseases are linked to the proteasome accessory complex?
Cancer, neurodegeneration (e.g., ALS, IBMPFD), and viral infections such as HIV and SARS-CoV-2.
What methods are used to study the proteasome accessory complex?
Affinity purification-mass spectrometry, CRISPR screens, live-cell imaging, and in vitro degradation assays.
Can CRISPR knockout be used to study proteasome accessory complex genes?
Yes, knockout of PSMD1, PSMC1, or CUL5 impairs degradation and viral replication, providing causal insights.
What is the 19S regulatory particle?
The 19S regulatory particle is the main proteasome accessory complex in eukaryotes, capping the 20S core and mediating substrate entry.
How do viruses hijack the proteasome accessory complex?
HIV-2 Vpx and SARS-CoV-2 ORF9b exploit Cullin 5-based complexes to degrade host restriction factors or regulate viral proteins.
Why is the proteasome accessory complex a drug target?
It controls degradation of pro-survival and pro-apoptotic proteins, and its inhibition is effective in multiple myeloma and other cancers.
Conclusion
The proteasome accessory complex (GO:0022624) is a critical regulator of protein degradation, capping the 20S core and governing substrate entry and exit. Its components, including 19S subunits and accessory proteins like p97/VCP and RAD23A/B, are implicated in cancer, neurodegeneration, and viral infections. CRISPR-based models are indispensable for dissecting its function and for developing targeted therapies. EDITGENE offers comprehensive services to accelerate this research.
References
- 1. Dahlmann B. 2005. Proteasomes.. Essays Biochem 41:31-48 PMID: 16250896
- 3. Wang Z et al.. 2022. HECT ubiquitin ligases as accessory proteins of the plant proteasome.. Essays Biochem 66(2):135-145 PMID: 35635104
- 4. Ding Y et al.. 2025. Substrate structure determines p97- and RAD23A/B-mediated proteasomal degradation in human cells.. J Biochem 178(5):341-353 PMID: 40795920
- 6. Zhou Y et al.. 2024. A Cullin 5-based complex serves as an essential modulator of ORF9b stability in SARS-CoV-2 replication.. Signal Transduct Target Ther 9(1):159 PMID: 38937432
- 7. Wang Z et al.. 2023. Analysis of Proteasome-Associated Ubiquitin Ligase Activity.. Methods Mol Biol 2581:57-67 PMID: 36413310
- 8. Miyakawa K et al.. 2025. PHD3-VHL axis controls HIV-2 infection through oxygen-dependent hydroxylation and degradation of Vpx.. PLoS Pathog 21(6):e1013241 PMID: 40522994
