GO:1990666 PCSK9-LDLR complex: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:1990666 describes the PCSK9-LDLR complex, a protein assembly in which the secreted protease PCSK9 binds the epidermal growth factor-like repeat A (EGF-A) domain of the low-density lipoprotein receptor (LDLR).
• Formation of the PCSK9-LDLR complex targets LDLR for degradation through the endosome/lysosome pathway, thereby reducing hepatic clearance of low-density lipoprotein cholesterol (LDL-C).
• The interaction is pH-sensitive: PCSK9 binds LDLR at the cell surface and the complex is stabilized in the acidic endosomal environment, a property that has been explored for therapeutic modulation.
• Beyond cholesterol homeostasis, the PCSK9-LDLR axis influences LDLR-mediated T-cell receptor recycling and antitumor CD8+ T cell activity.
• Additional proteins such as HFE, HLA-C, CAP1, APP, APLP2 and LRP1 modulate PCSK9-LDLR trafficking and function, but are not strictly required for PCSK9-mediated LDLR degradation in vivo.
• CRISPR-based knockout, point-mutation, knock-in and overexpression models enable causal dissection of PCSK9-LDLR complex components and their disease relevance.
Description
The PCSK9-LDLR complex (GO:1990666) is a cellular component defined as a protein complex consisting of the serine protease PCSK9 (proprotein convertase subtilisin/kexin-9) and a low-density lipoprotein receptor (LDLR). Interaction typically occurs through the epidermal growth factor-like repeat A (EGF-A) domain of the LDLR, and complex formation promotes degradation of the LDLR through the endosome/lysosome pathway. This complex is central to plasma cholesterol regulation because LDLR is the principal receptor mediating hepatic uptake of LDL-C, and PCSK9 binding reduces LDLR availability. For researchers, GO:1990666 provides a precise annotation for studying protein-protein interactions, trafficking, and therapeutic intervention in dyslipidemia and cardiovascular disease. The complex is also relevant beyond lipid metabolism: inhibiting PCSK9 to promote LDLR-mediated TCR recycling and signaling potentiates CD8+ T cell antitumor activity. Structural and mutational studies have mapped disruptive mutations in the PCSK9-LDLR interface, offering templates for functional interrogation. This article synthesizes authoritative QuickGO annotation and verified PubMed literature to describe the composition, assembly, regulation, disease links, and experimental methods for studying the PCSK9-LDLR complex, with emphasis on CRISPR-based models for causal gene analysis.
PCSK9-LDLR complex At A Glance
| GO ID | GO:1990666 |
|---|---|
| GO term | PCSK9-LDLR complex |
| Ontology | cellular_component |
| Synonym | PCSK9:EGF-A complex; PCSK9.LDLR complex; PCSK9/LDL-R complex; PCSK9:low-density lipoprotein receptor complex |
| Major function | Binding of PCSK9 to LDLR EGF-A domain, promoting LDLR degradation via endosome/lysosome pathway |
| Complex components | PCSK9 (serine protease) and LDLR (low-density lipoprotein receptor) |
| Interaction domain | Epidermal growth factor-like repeat A (EGF-A) domain of LDLR |
| Cellular context | Cell surface binding followed by endosomal/lysosomal trafficking |
| Disease relevance | Hypercholesterolemia, cardiovascular disease, cancer immunotherapy |
What Is GO:1990666?
GO:1990666 (PCSK9-LDLR complex) is a cellular component term describing a heteromeric protein complex formed by PCSK9 and an LDLR molecule. Binding typically involves the EGF-A domain of LDLR, and the resulting complex directs LDLR toward endosomal/lysosomal degradation, thereby reducing LDLR-mediated LDL-C uptake.
Why Is PCSK9-LDLR complex Important in Cell Biology?
The PCSK9-LDLR complex is a key node in cholesterol homeostasis and a validated therapeutic target: disrupting the complex increases LDLR availability and lowers plasma LDL-C. It also exemplifies pH-sensitive protein-protein interactions that can be engineered for enhanced hepatic LDL-C uptake. Its roles in T-cell biology and cancer immunotherapy broaden its biomedical significance.
• Controls hepatic LDLR levels and plasma LDL-C clearance.
• Provides a structural template for disruptive mutations at the PCSK9-LDLR interface.
• Exhibits pH-sensitive binding that can be modified to enhance LDL-C uptake.
• Influences LDLR-mediated TCR recycling and CD8+ T cell antitumor activity.
• Is modulated by MHC-I proteins HFE and HLA-C, linking lipid metabolism to immune regulation.
• Interacts with CAP1 and HLA-C, which regulate LDLR levels.
• APP, APLP2 and LRP1 interact with PCSK9 but are not required for LDLR degradation in vivo.
• PCSK9 mutations and C-terminal domain affect trafficking dynamics of LDLR degradation.
• Serves as a model for studying endosomal sorting and lysosomal targeting.
• Enables CRISPR-based functional genomics of lipid and immune pathways.
Structure and Composition of PCSK9-LDLR complex
PCSK9 binding to the LDLR EGF-A domain
In simple terms: PCSK9 grabs onto a specific part of the LDL receptor called EGF-A.
The PCSK9-LDLR complex forms when the serine protease PCSK9 binds the epidermal growth factor-like repeat A (EGF-A) domain of LDLR. This interaction is the initiating event that commits LDLR to degradation.
pH-sensitive interaction and endosomal stabilization
In simple terms: The bond between PCSK9 and LDLR gets stronger in the acidic environment inside the cell.
The PCSK9-LDLR interaction is pH-sensitive, with binding at the cell surface and stabilization in the acidic endosomal compartment. Modifying this pH sensitivity has been proposed as a strategy to enhance hepatic cell uptake of LDL-C.
Trafficking dynamics and C-terminal domain
In simple terms: After binding, the complex moves through the cell, and PCSK9's tail helps direct this journey.
Trafficking dynamics of PCSK9-induced LDLR degradation depend on human PCSK9 mutations and the C-terminal domain, which influence the route to lysosomes.
Modulation by MHC-I proteins HFE and HLA-C
In simple terms: Other immune-related proteins can influence how PCSK9 and LDLR interact.
HFE and HLA-C differentially regulate PCSK9-LDLR trafficking and LDLR levels, linking the complex to MHC-I biology. CAP1 and HLA-C also functionally regulate LDLR levels through interactions with PCSK9.
Additional interacting proteins: APP, APLP2, LRP1
In simple terms: Some proteins bind PCSK9 but are not required for LDLR breakdown.
APP, APLP2 and LRP1 interact with PCSK9 but are not required for PCSK9-mediated degradation of the LDLR in vivo, indicating that the core PCSK9-LDLR complex is sufficient for this function.
Key Genes Involved in GO:1990666 PCSK9-LDLR complex
The following genes and proteins are central to the formation, regulation, and study of the PCSK9-LDLR complex.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PCSK9 | Serine protease that binds LDLR EGF-A domain | Core component; target for mutations and inhibitors |
| LDLR | Low-density lipoprotein receptor; binds PCSK9 | Core component; mediates LDL-C uptake |
| HFE | MHC-I-like protein modulating PCSK9-LDLR trafficking | Regulates LDLR levels |
| HLA-C | MHC-I protein interacting with PCSK9 | Functional regulation of LDLR levels |
| CAP1 | Adenylyl cyclase-associated protein 1 | Interacts with PCSK9 to regulate LDLR |
| APP | Amyloid precursor protein | Interacts with PCSK9 but not required for LDLR degradation |
| APLP2 | Amyloid precursor-like protein 2 | Interacts with PCSK9 but not required for LDLR degradation |
| LRP1 | LDL receptor-related protein 1 | Interacts with PCSK9 but not required for LDLR degradation |
| CD8A | T cell co-receptor | LDLR-mediated TCR recycling in CD8+ T cells |
| TCR | T cell receptor | Recycling and signaling modulated by PCSK9-LDLR axis |
| SREBF2 | Sterol regulatory element-binding factor 2 | Regulates cholesterol homeostasis genes |
| HMGCR | HMG-CoA reductase | Cholesterol synthesis; related to LDLR pathway |
| NPC1L1 | Niemann-Pick C1-like 1 | Cholesterol absorption; related to lipid metabolism |
| APOB | Apolipoprotein B | Ligand for LDLR; related to LDL-C |
| MYLIP | E3 ubiquitin ligase IDOL | Regulates LDLR degradation |
| PCSK7 | Proprotein convertase 7 | Related protease family member |
| FURIN | Proprotein convertase | Related protease family member |
| SORT1 | Sortilin 1 | Modulates PCSK9 secretion |
How Is PCSK9-LDLR complex Regulated?
The PCSK9-LDLR complex is regulated at multiple levels. PCSK9 binding to LDLR is pH-sensitive, with stabilization in acidic endosomes. MHC-I proteins HFE and HLA-C differentially modulate PCSK9-LDLR trafficking and LDLR levels. CAP1 and HLA-C functionally regulate LDLR levels through interactions with PCSK9. PCSK9 mutations and the C-terminal domain influence trafficking dynamics of LDLR degradation. Additionally, APP, APLP2 and LRP1 interact with PCSK9 but are not required for LDLR degradation in vivo.
PCSK9-LDLR complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| PCSK9 | Hypercholesterolemia, cardiovascular disease | PCSK9 knockout or point-mutation cell lines |
| LDLR | Familial hypercholesterolemia | LDLR knockout or knock-in models |
| HFE | Iron metabolism and lipid crosstalk | HFE knockout or overexpression |
| HLA-C | Immune regulation and LDLR levels | HLA-C knockout or overexpression |
| CD8A | Cancer immunotherapy | CD8+ T cell knockout models |
Hypercholesterolemia and cardiovascular disease
The PCSK9-LDLR complex reduces LDLR availability, leading to decreased hepatic LDL-C clearance and elevated plasma cholesterol. Modifying pH-sensitive PCSK9/LDLR interactions has been explored as a strategy to enhance hepatic cell uptake of LDL-C.
Cancer immunotherapy
Inhibiting PCSK9 promotes LDLR-mediated TCR recycling and signaling, potentiating CD8+ T cell antitumor activity. This links the PCSK9-LDLR complex to immune checkpoint regulation and cancer therapy.
Immune and lipid crosstalk
HFE and HLA-C, both MHC-I proteins, differentially regulate PCSK9-LDLR trafficking, suggesting a connection between lipid metabolism and immune regulation. CAP1 and HLA-C also modulate LDLR levels.
From PCSK9-LDLR complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does PCSK9 binding to LDLR require EGF-A domain? | LDLR point-mutation (EGF-A domain) knock-in |
| What is the effect of PCSK9 loss on LDLR levels? | PCSK9 knockout cell line |
| How do PCSK9 mutations affect LDLR degradation? | PCSK9 point-mutation overexpression |
| Does HLA-C regulate PCSK9-LDLR trafficking? | HLA-C knockout or overexpression |
| Is LDLR required for PCSK9-mediated TCR recycling? | LDLR knockout in CD8+ T cells |
| Can tagged PCSK9 track complex trafficking? | Tagged knock-in of PCSK9 |
How to Study the PCSK9-LDLR complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Co-immunoprecipitation | Physical interaction between PCSK9 and LDLR | Complex formation validation |
| Surface plasmon resonance | Binding affinity and kinetics | pH-sensitive interaction studies |
| Live-cell imaging | Trafficking and degradation dynamics | Endosome/lysosome pathway |
| LDL-C uptake assay | Functional LDLR activity | Hepatic cell uptake |
| CRISPR knockout screen | Genes required for complex function | Modifier discovery |
| RNA-seq | Transcriptional changes | Pathway analysis |
| Proteomics | Protein abundance and interactions | Complex composition |
Protein-protein interaction assays
Co-immunoprecipitation, pull-down, and surface plasmon resonance can detect and quantify PCSK9-LDLR complex formation, including pH-dependent binding. In silico modeling of disruptive mutations at the interface guides experimental design.
Trafficking and imaging
Fluorescence microscopy and live-cell imaging with tagged PCSK9 and LDLR track endosomal/lysosomal trafficking and degradation dynamics. pH-sensitive probes can monitor complex stability in endosomes.
Functional LDL-C uptake assays
LDL-C uptake assays in hepatic cells measure the functional consequence of PCSK9-LDLR complex modulation, such as enhanced uptake after modifying pH sensitivity.
CRISPR screening and bioinformatics
Genome-wide CRISPR knockout screens combined with bioinformatics can identify modifiers of PCSK9-LDLR function and LDLR levels. Transcriptomic and proteomic analyses reveal downstream effects.
How CRISPR Can Be Used to Study GO:1990666 PCSK9-LDLR complex
Knockout
CRISPR knockout of PCSK9 or LDLR abolishes the PCSK9-LDLR complex, enabling studies of LDLR levels and LDL-C uptake. Knockout of modifiers such as HFE or HLA-C reveals their roles in complex regulation.
Point Mutation
Point mutations at the PCSK9-LDLR interface, guided by in silico predictions, can disrupt or stabilize the complex to test structure-function relationships. PCSK9 mutations affecting trafficking can be introduced to study degradation dynamics.
Knock-in
Knock-in of tagged PCSK9 or LDLR allows tracking of the complex in live cells and identification of interacting partners. EGF-A domain knock-in mutations test the requirement of this domain for binding.
Overexpression
Overexpression of PCSK9 or LDLR variants can enhance complex formation and drive LDLR degradation, useful for biochemical and imaging assays. Overexpression of HLA-C or CAP1 modulates LDLR levels.
How EDITGENE Supports PCSK9-LDLR complex Research
Researchers studying PCSK9-LDLR complex-related genes often need to determine whether a candidate gene is causally involved in complex formation, trafficking, or degradation. EDITGENE provides CRISPR-based cell model services to enable such causal experiments.
Contact EDITGENE today to design your custom CRISPR model for PCSK9-LDLR complex research.
Frequently Asked Questions About PCSK9-LDLR complex
What is the PCSK9-LDLR complex?
The PCSK9-LDLR complex (GO:1990666) is a protein complex of PCSK9 and the low-density lipoprotein receptor (LDLR) that forms through the LDLR EGF-A domain and promotes LDLR degradation via the endosome/lysosome pathway.
What genes are involved in the PCSK9-LDLR complex?
Core genes are PCSK9 and LDLR; modifiers include HFE, HLA-C, CAP1, APP, APLP2, and LRP1.
How does PCSK9 binding lead to LDLR degradation?
PCSK9 binds LDLR at the cell surface, the complex is stabilized in acidic endosomes, and LDLR is routed to lysosomes for degradation.
Why is the PCSK9-LDLR complex important for cholesterol?
It reduces LDLR availability, decreasing hepatic LDL-C uptake and raising plasma cholesterol.
Is the PCSK9-LDLR interaction pH-sensitive?
Yes, the interaction is pH-sensitive, with binding at neutral pH and stabilization in acidic endosomes.
What role does the EGF-A domain play?
The EGF-A domain of LDLR is the primary binding site for PCSK9 in the complex.
Can PCSK9 inhibition affect cancer immunotherapy?
Inhibiting PCSK9 promotes LDLR-mediated TCR recycling and signaling, potentiating CD8+ T cell antitumor activity.
What experimental models study the PCSK9-LDLR complex?
CRISPR knockout, point-mutation, knock-in, and overexpression cell models, along with biochemical and imaging assays, are commonly used.
Do APP, APLP2, and LRP1 affect PCSK9-LDLR degradation?
They interact with PCSK9 but are not required for PCSK9-mediated LDLR degradation in vivo.
How do HFE and HLA-C regulate the PCSK9-LDLR complex?
HFE and HLA-C differentially modulate PCSK9-LDLR trafficking and LDLR levels.
Conclusion
The PCSK9-LDLR complex (GO:1990666) is a central molecular assembly in cholesterol homeostasis and a model for pH-sensitive protein-protein interactions. Its study spans lipid metabolism, immune regulation, and cancer immunotherapy. CRISPR-based models and bioinformatics are powerful tools to dissect its components and disease relevance.
References
- 1. Martin WR et al.. 2020. In Silico Insights into Protein-protein Interaction Disruptive Mutations in the PCSK9-LDLR complex.. Int J Mol Sci 21(5) PMID: 32106405
- 2. Yuan J et al.. 2021. Potentiating CD8(+) T cell antitumor activity by inhibiting PCSK9 to promote LDLR-mediated TCR recycling and signaling.. Protein Cell 12(4):240-260 PMID: 33606190
- 3. Mikaeeli S et al.. 2024. Insights into PCSK9-LDLR Regulation and Trafficking via the Differential Functions of MHC-I Proteins HFE and HLA-C.. Cells 13(10) PMID: 38786080
- 4. Ben-Naim L et al.. 2022. Modifying pH-sensitive PCSK9/LDLR interactions as a strategy to enhance hepatic cell uptake of low-density lipoprotein cholesterol (LDL-C).. Protein Eng Des Sel 35 PMID: 35174858
- 5. Tavori H et al.. 2015. On the function and homeostasis of PCSK9: reciprocal interaction with LDLR and additional lipid effects.. Atherosclerosis 238(2):264-70 PMID: 25544176
- 6. Poirier S et al.. 2016. Trafficking Dynamics of PCSK9-Induced LDLR Degradation: Focus on Human PCSK9 Mutations and C-Terminal Domain.. PLoS One 11(6):e0157230 PMID: 27280970
- 7. Fruchart Gaillard C et al.. 2023. Molecular interactions of PCSK9 with an inhibitory nanobody, CAP1 and HLA-C: Functional regulation of LDLR levels.. Mol Metab 67:101662 PMID: 36566984
- 8. Fu T et al.. 2017. APP, APLP2 and LRP1 interact with PCSK9 but are not required for PCSK9-mediated degradation of the LDLR in vivo.. Biochim Biophys Acta Mol Cell Biol Lipids 1862(9):883-889 PMID: 28495363
