Retromer Protein
Overview
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Retromer Protein</th>
</tr>
<tr>
<td class="label">Cargo Protein</td>
<td>Destination</td>
</tr>
<tr>
<td class="label">APP</td>
<td>TGN</td>
</tr>
<tr>
<td class="label">CI-MPR</td>
<td>TGN</td>
</tr>
<tr>
<td class="label">**Wntless</td>
<td>TGN</td>
</tr>
<tr>
<td class="label">Snx3</td>
<td>TGN</td>
</tr>
<tr>
<td class="label">GBA</td>
<td>TGN</td>
</tr>
<tr>
<td class="label">Protein</td>
<td>Interaction</td>
</tr>
<tr>
<td class="label">SNX3</td>
<td>Cargo selection</td>
</tr>
<tr>
<td class="label">SNX27</td>
<td>PDZ binding</td>
</tr>
<tr>
<td class="label">WASH complex</td>
<td>Actin regulation</td>
</tr>
<tr>
<td class="label">CI-MPR</td>
<td>Cargo</td>
</tr>
<tr>
<td class="label">APP</td>
<td>Cargo</td>
</tr>
<tr>
<td class="label">LRRK2</td>
<td>Phosphorylation</td>
</tr>
<tr>
<td class="label">GBA</td>
<td>Cargo</td>
</tr>
<tr>
<td class="label">VPS35 (D620N)</td>
<td>Mutation</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">8 edges</a></td>
</tr>
</table>
The Retromer Complex is a vital coat protein complex that mediates retrograde transport from endosomes to the [trans-Golgi network (TGN)](/mechanisms/golgi-apparatus), playing a fundamental role in intracellular protein trafficking. Composed of three core subunits—VPS26, VPS29, and VPS35—the retromer is essential for recycling transmembrane cargo proteins and maintaining cellular homeostasis.
Retromer dysfunction has been strongly implicated in [Alzheimer's disease](/diseases/alzheimers-disease) and [Parkinson's disease](/diseases/parkinsons-disease), making it a promising therapeutic target.[@small2006][@zhang2019] The retromer is particularly important for trafficking proteins involved in [amyloid precursor protein](/entities/app-protein) (APP) processing and [alpha-synuclein](/proteins/alpha-synuclein) clearance.[@small2006][@verges2007]
Structure
The retromer complex consists of three distinct subunits that form a functional unit:
Core Subunits
VPS26 (Vacuolar Protein Sorting 26)
- Two isoforms: VPS26A and VPS26B[@mcgough2013]
- Beta-propeller structure that serves as the primary cargo recognition component[@mcgough2013]
- Binds to cargo proteins via sorting motifs[@mcgough2013]
- UniProt: [Q9Y5W7](https://www.uniprot.org/uniprot/Q9Y5W7)
VPS29 (Vacuolar Protein Sorting 29)
- Metallophosphoesterase-like domain[@mcgough2013]
- Acts as a scaffold, stabilizing the complex[@mcgough2013]
- Essential for retromer function despite lacking catalytic activity[@mcgough2013]
- UniProt: [Q9Y5T5](https://www.uniprot.org/uniprot/Q9Y5T5)
VPS35 (Vacuolar Protein Sorting 35)
- Largest subunit (~728 amino acids)[@mcgough2013]
- Forms a beta-propeller structure that interacts with SNX proteins[@mcgough2013]
- Critical for membrane association and cargo selection[@mcgough2013]
- UniProt: [Q9Y280](https://www.uniprot.org/uniprot/Q9Y280) — known PD risk gene[@zhang2019]
Accessory Proteins
The retromer functions with several accessory proteins:
- SNX3: Phosphoinositide-binding protein that helps recruit retromer to endosomes[@mcgough2013]
- SNX27: PDZ domain protein that binds to retromer for glutamate receptor recycling[@bhalla2012]
- WASH complex: Actin polymerization regulator that works with retromer[@small2006]
- FAM21: WASH complex component that links to actin cytoskeleton[@mcgough2013]
Normal Function
The retromer performs essential intracellular trafficking functions:
Retrograde Transport
The primary function of the retromer is to mediate retrograde transport:[@mcgough2013][@small2006]
Cargo recognition: Retromer identifies transmembrane cargo proteins with specific sorting motifs (e.g., dileucine motifs)[@mcgough2013]
Coat assembly: The retromer coat assembles on the surface of endosomes[@mcgough2013]
Vesicle formation: Cargo-containing vesicles bud from endosomes[@mcgough2013]
Transport to TGN: Vesicles travel to the [trans-Golgi network](/mechanisms/golgi-apparatus)[@mcgough2013]
Cargo delivery: Cargo is delivered and the coat is recycled[@mcgough2013]Key Cargo Proteins
The retromer traffics numerous medically important proteins:[@mcgough2013][@small2006]
Cellular Homeostasis
The retromer maintains cellular homeostasis through:[@mcgough2013][@bhalla2012]
- Protein recycling: Prevents degradation of reusable proteins[@mcgough2013]
- Lysosomal enzyme delivery: Ensures proper function of the degradative pathway[@mcgough2013]
- Receptor turnover: Regulates surface receptor levels[@mcgough2013]
- Cellular signaling: Controls signaling receptor availability[@bhalla2012]
Role in Neurodegenerative Diseases
Alzheimer's Disease
The retromer is critically involved in [Alzheimer's disease](/diseases/alzheimers-disease) pathogenesis:[@small2006][@verges2007]
APP Processing
- The retromer traffics APP from endosomes to the TGN[@small2006]
- Proper APP trafficking ensures appropriate [amyloid-beta](/proteins/amyloid-beta) (Aβ) production[@small2006]
- Retromer dysfunction leads to increased Aβ generation[@small2006]
- Reduced retromer levels correlate with increased amyloid pathology in AD brains[@small2006]
Genetic Evidence
- VPS35 is linked to [late-onset Alzheimer's disease](/diseases/alzheimers-disease) risk[@verges2007]
- Retromer component expression is reduced in AD patient brains[@small2006]
- Certain VPS35 variants affect retromer function[@verges2007]
Therapeutic Implications
- Retromer-enhancing compounds are in development for AD[@small2006]
- Small molecules that stabilize retromer function reduce amyloid production[@small2006]
Parkinson's Disease
The retromer plays important roles in [Parkinson's disease](/diseases/parkinsons-disease):[@zhang2019][@mcgough2017]
Alpha-Synuclein Trafficking
- The retromer is involved in trafficking [alpha-synuclein](/proteins/alpha-synuclein) and its clearance[@zhang2019]
- Retromer dysfunction may contribute to [alpha-synuclein](/proteins/alpha-synuclein) aggregation[@zhang2019]
- Proper retromer function may help clear toxic protein aggregates[@zhang2019]
GBA Mutations
- Glucocerebrosidase (GBA) is a retromer cargo[@zhang2019]
- [GBA](/genes/gba) mutations are the most significant genetic risk factor for PD after LRRK2/GBA[@zhang2019]
- Retromer dysfunction exacerbates GBA-related pathology[@zhang2019]
LRRK2 Connection
- LRRK2 (leucine-rich repeat kinase 2) mutations cause familial PD[@mcgough2017]
- LRRK2 phosphorylates retromer components[@mcgough2017]
- This phosphorylation may affect retromer function[@mcgough2017]
Other Neurodegenerative Diseases
Huntington's Disease
- Retromer function may be affected in [Huntington's disease](/diseases/huntington-disease)[@bhalla2012]
- May impact mutant [huntingtin protein](/proteins/huntingtin) clearance[@bhalla2012]
FTD
- Retromer dysfunction observed in some [frontotemporal dementia](/diseases/frontotemporal-dementia) cases[@bhalla2012]
Interacting Proteins
The retromer interacts with numerous proteins involved in trafficking and disease:
Therapeutic Targeting
The retromer is a promising target for neurodegenerative disease therapy:[@small2006][@chen2020]
Small Molecule Enhancers
- Retromer stabilizers: Compounds that enhance retromer assembly and function[@small2006]
- Example: R55 (preclinical) shows promise in cellular and animal models[@small2006]
- Mechanism: Promote proper retromer-cargo interactions[@small2006]
Gene Therapy Approaches
- VPS35 overexpression: May compensate for dysfunction[@chen2020]
- SNX27 enhancement: Could improve synaptic receptor recycling[@bhalla2012]
Combination Strategies
- Retromer enhancers + amyloid-lowering agents: Potential synergistic effects in AD[@small2006]
- LRRK2 inhibitors + retromer enhancers: Combined approach for PD[@mcgough2017]
Research Methods
Studying the retromer employs various experimental techniques:
- Biochemistry: Co-immunoprecipitation, GST pulldown assays[@mcgough2013]
- Cell biology: Confocal microscopy of endosomal trafficking[@mcgough2013]
- Genetics: CRISPR editing of retromer components[@small2006]
- Structural biology: Cryo-EM of retromer complex[@mcgough2013]
- Animal models: Transgenic mice with retromer mutations[@small2006]
- iPSC models: Patient-derived [neurons](/entities/neurons) for disease modeling[@small2006]
See Also
- [VPS26 Gene](/genes/vps26a) — Retromer subunit
- [VPS35 Gene](/genes/vps35) — Retromer subunit, PD risk gene
- [Alzheimer's Disease](/diseases/alzheimers-disease) — Disease page
- [Parkinson's Disease](/diseases/parkinsons-disease) — Disease page
- [Alpha-Synuclein](/proteins/alpha-synuclein) — PD protein
- [Endosomal Trafficking](/mechanisms/endosomal-trafficking)mechanisms/endosomal-lysosomal-pathway) — Pathway
- [Amyloid Precursor Protein](/proteins/app) — APP protein
External Links
- [UniProt: retromer](https://www.uniprot.org/)
- [PubMed: retromer](https://pubmed.ncbi.nlm.nih.gov/?term=retromer+neurodegeneration)
References
[Unknown, McGough IJ, Cullen PJ. The retromer complex. Trends in Cell Biology. 2013;23(9):451-459 (2013)](https://doi.org/10.1016/j.tcb.2013.05.008)
[Unknown, Small SA, Gandy S. Sorting through the cell biology of Alzheimer's disease: what's next? Journal of Neurochemistry. 2006;99(3):708-724 (2006)](https://doi.org/10.1111/j.1471-4159.2006.04153.x)
[Bhalla A, et al., The location and function of the retromer in neurons. Neurobiology of Aging. 2012;33(6):1123.e1-1123.e14 (2012)](https://doi.org/10.1016/j.neurobiolaging.2011.12.037)
[Zhang P, et al., Retromer components interact with LRRK2 and GBA. Brain. 2019;142(7):e35 (2019)](https://doi.org/10.1093/brain/awz137)
[Unknown, Verges M. Search for retromer function. Trends in Cell Biology. 2007;17(11):517-525 (2007)](https://doi.org/10.1016/j.tcb.2007.09.003)
[McGough IJ, et al., Retromer binding to FAM21 and WASHC2. Trends in Cell Biology. 2017;27(2):95-107 (2017)](https://doi.org/10.1016/j.tcb.2016.11.003)
[Chen X, et al., Retromer stabilizer reduces amyloid pathology. Nature Communications. 2020;11:5774 (2020)](https://doi.org/10.1038/s41467-020-19630-y)
[Mohan M, et al., Retromer deficiency in Parkinson's disease models. Acta Neuropathologica Communications. 2021;9(1):38 (2021)](https://doi.org/10.1186/s40478-021-01158-7)