PSEN2 Protein (Presenilin-2)

PSEN2 Protein (Presenilin-2)

Pathway Diagram

```mermaid
flowchart TD
PSEN2["PSEN2<br/>(Presenilin 2)"]

PSEN1["PSEN1<br/>(Presenilin 1)"]
PEN2["PEN2<br/>(Gamma-secretase<br/>component)"]
MAPT["MAPT<br/>(Tau protein)"]

AmyloidBeta["Amyloid-beta<br/>(Abeta peptide)"]
GammaSecretase["gamma-Secretase<br/>Complex"]

EOAD["Early-onset<br/>Alzheimer's Disease"]
AD["Alzheimer's<br/>Disease"]
Neurodegeneration["Neurodegeneration"]

AmyloidPlaques["Amyloid<br/>Plaques"]
TauTangles["Tau<br/>Tangles"]

A2M["A2M<br/>(Alpha-2-Macroglobulin)"]
DHCR24["DHCR24<br/>(Cholesterol<br/>synthesis)"]
PARP1["PARP1<br/>(DNA repair)"]

CognitiveDecline["Cognitive<br/>Decline"]
Apoptosis["Neuronal<br/>Death"]

PSEN2 -->|"forms"| GammaSecretase
PSEN1 -->|"forms"| GammaSecretase
PEN2 -->|"forms"| GammaSecretase

PSEN2 -->|"regulates"| AmyloidBeta
GammaSecretase -->|"cleaves APP to produce"| AmyloidBeta

PSEN2 -->|"activates"| MAPT
MAPT -->|"forms"| TauTangles

PSEN2 -->|"causes"| EOAD
PSEN2 -->|"causes"| AD
AmyloidBeta -->|"aggregates into"| AmyloidPlaques

AmyloidPlaques -->|"leads to"| Neurodegeneration
TauTangles -->|"leads to"| Neurodegeneration
Neurodegeneration -->|"results in"| CognitiveDecline
Neurodegeneration -->|"results in"| Apoptosis

A2M -->|"interacts with"| PSEN2
DHCR24 -->|"interacts with"| PSEN2
PARP1 -->|"interacts with"| PSEN2

style PSEN2 fill:#006494
style AmyloidBeta fill:#ef5350

PSEN2 Protein (Presenilin-2)

Pathway Diagram

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">PSEN2 — Presenilin-2</th>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Presenilin 2</td>
</tr>
<tr>
<td class="label">Gene</td>
<td>[PSEN2](/genes/psen2)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/O00287" target="_blank">O00287</a></td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>1q42.13</td>
</tr>
<tr>
<td class="label">Protein Type</td>
<td>Aspartyl protease (catalytic subunit)</td>
</tr>
<tr>
<td class="label">Complex</td>
<td>[Gamma-secretase](/proteins/gamma-secretase)</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~50 kDa (448 aa)</td>
</tr>
<tr>
<td class="label">Key Diseases</td>
<td>[Alzheimer's Disease](/diseases/alzheimers), [Parkinson's Disease](/diseases/parkinsons-disease)</td>
</tr>
<tr>
<th class="infobox-subheader" colspan="2">Key Mutations</th>
</tr>
<tr>
<td colspan="2" style="font-size:0.85em">N141I (Volga German), M239V, T122P, M239I, A85V, R62H</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ad" style="color:#ef9a9a">AD</a>, <a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/ami" style="color:#ef9a9a">AMI</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">367 edges</a></td>
</tr>
</table>

PSEN2 Protein (Presenilin-2)

Overview

Presenilin-2 (PSEN2) is an integral membrane aspartyl protease that serves as the catalytic subunit of the gamma-secretase complex, similar to its homolog [PSEN1](/proteins/psen1). PSEN2 is encoded by the [PSEN2 gene](/genes/psen2) located on chromosome 1q42.13 (NCBI Gene ID: [5664](https://www.ncbi.nlm.nih.gov/gene/5664), UniProt: [O00287](https://www.uniprot.org/uniprot/O00287)).

While less frequently mutated than PSEN1, pathogenic PSEN2 mutations cause familial Alzheimer's disease (FAD) and have been implicated in [Parkinson's disease](/diseases/parkinsons-disease) and other neurodegenerative disorders. PSEN2 shares significant structural and functional homology with PSEN1 but exhibits distinct expression patterns and physiological roles.

Structure

Topology

Presenilin-2 is a polytopic membrane protein with:

• Nine transmembrane domains (TMD 1-9) traversing the lipid bilayer
• N-terminal region: Cytoplasmic domain with distinct sequence from PSEN1
• Large hydrophilic loop between TMD6 and TMD7 containing the endoproteolysis site
• C-terminal region: Critical for complex assembly

Catalytic Core

The active site consists of two essential aspartyl residues:

• Asp257 (in TMD 6)
• Asp385 (in TMD 7)

Protease Domain

• The enzyme adopts a horseshoe-shaped structure within the membrane
• Active site residues are positioned within a membrane-spanning cavity
• Lateral openings in transmembrane domains allow substrate access

Comparison with PSEN1

PSEN2 and PSEN1 have highly similar overall structures. Key differences:

• N-terminal region divergence
• Loop variations between transmembrane domains
• PSEN2 is 19 amino acids shorter (448 vs 467 aa)

The Gamma-Secretase Complex

PSEN2 functions exclusively as part of the gamma-secretase complex. Unlike PSEN1, PSEN2 is incorporated into a distinct variant of the complex.

Complex Composition

| Subunit | Gene | Function |
|---------|------|----------|
| Presenilin 2 | PSEN2 | Catalytic aspartyl protease |
| Aph-1 | APH1A/APH1B | Stabilizes complex |
| Pen-2 | PSENEN | Required for activation |
| Nicastrin | NCSTN | Substrate recognition |

Assembly

γ-42 vs γ-41 Complexes

• PSEN1-containing complexes (γ-41): Generate predominantly Aβ40/41
• PSEN2-containing complexes (γ-42): Have distinct substrate affinities and produce more Aβ42

Function

APP Processing

PSEN2/gamma-secretase cleaves [APP](/proteins/amyloid-beta) to produce amyloid-beta peptides:

Aβ42/Aβ40 Ratio

• PSEN2 mutations shift cleavage toward longer Aβ species
• Increased Aβ42/Aβ40 ratio promotes aggregation and plaque formation
• Similar pathogenic mechanism to PSEN1 mutations

Other Substrates

Gamma-secretase cleaves numerous substrates beyond APP:

• Notch receptors — cell fate and development
• E-cadherin — cell adhesion
• LDL receptor family — lipid metabolism
• Ephrin receptors — neuronal guidance
• Synaptic proteins — synaptic function

Expression Pattern

Unlike PSEN1, PSEN2 has a more restricted tissue distribution:

• Brain: Highest in hippocampus, cortex, basal ganglia neurons
• Peripheral: Significant expression in heart, skeletal muscle, pancreas
• Cellular: Both neurons and non-neuronal cells

Pathogenic Mutations

Mutation Spectrum

Over 40 pathogenic PSEN2 mutations have been identified, causing early-onset FAD with some unique features:

• Age of onset: Typically 55-75 years (later than PSEN1)
• Penetrance: Generally lower than PSEN1
• Clinical features: Classic AD, sometimes with atypical presentations
• Phenotypic variability: Greater variability than PSEN1 mutations

Key Mutations

| Mutation | Location | Origin/Effect |
|----------|----------|---------------|
| N141I | TMD 2 | Volga German families, most common |
| M239V | TMD 4 | Typical AD phenotype |
| T122P | TMD 3 | Severe, early onset |
| M239I | TMD 4 | Aggressive phenotype |
| A85V | TMD 2 | Late onset |
| R62H | N-terminus | Reduced penetrance |

Volga German Mutation

The N141I mutation is the most studied PSEN2 mutation:

• Identified in Volga German families with high incidence of AD
• Age of onset: 65-70 years (later than PSEN1)
• May present with spastic paraparesis in some families
• Produces Aβ42 with increased aggregation potential

Molecular Mechanisms

FAD mutations affect PSEN2 function through:

Clinical Significance

Alzheimer's Disease

• FAD cause: Second most common presenilin gene after PSEN1
• Phenotype: Progressive memory decline, cognitive impairment
• Neuropathology: Amyloid plaques, neurofibrillary tangles
• Age of onset: Generally later than PSEN1 (average 65-70 years)

Parkinson's Disease

• Lewy body pathology: Some PSEN2 mutations associated with Lewy bodies
• Synucleinopathy: Links to [alpha-synuclein](/proteins/alpha-synuclein) pathology
• Complex relationship: May influence protein aggregation pathways

Diagnostic Importance

• Genetic testing: Indicated for early-onset AD families
• Differential diagnosis: Helps distinguish FAD from other dementias
• Family screening: Enables predictive testing for at-risk relatives

Therapeutic Implications

• Gamma-secretase targeting: Similar strategies to PSEN1
• Modulators: GSMs may be effective for PSEN2 mutants
• Immunotherapy: Aβ-targeting approaches applicable
• Challenge: PSEN2-specific targeting is complex due to complex heterogeneity

Interactions

Protein-Protein Interactions

| Partner | Interaction | Effect |
|---------|-------------|--------|
| [APP](/proteins/amyloid-beta) | Substrate | Primary substrate |
| Nicastrin | Complex subunit | Substrate recognition |
| Aph-1 | Complex subunit | Complex stability |
| Pen-2 | Complex subunit | Activation |
| Notch | Substrate | Signaling regulation |
| [BACE1](/proteins/bace1) | Sequential processing | Upstream cleavage |

Pathway Participation

• Amyloidogenic processing: Aβ production pathway
• Notch signaling: Developmental pathways
• Calcium signaling: ER calcium homeostasis
• Protein quality control: UPR pathways

Research and Models

Animal Models

• Transgenic mice: PSEN2 mutant lines (N141I, M239V)
• Knockout mice: PSEN2-deficient models show subtle phenotypes
• Double mutants: APP/PSEN2 crosses for amyloid studies

Cell Systems

• Patient-derived cells: Fibroblasts from mutation carriers
• iPSC neurons: Induced pluripotent stem cell-derived neurons
• Overexpression systems: Wild-type and mutant PSEN2 expression

Biomarkers

• CSF Aβ42/40: May show elevated ratio in PSEN2 carriers
• Neuroimaging: Early hippocampal atrophy
• Clinical: Earlier age of onset than sporadic AD

Key Publications

See Also

• [PSEN2 Gene](/genes/psen2) — Gene-level information
• [PSEN1 Protein](/proteins/psen1) — Presenilin 1
• [Gamma-Secretase](/proteins/gamma-secretase) — The complete complex
• [Amyloid-Beta](/proteins/amyloid-beta) — Aβ peptide products
• [Alzheimer's Disease](/diseases/alzheimers-disease) — Target disease
• [Parkinson's Disease](/diseases/parkinsons-disease) — Associated disease
• [BACE1](/proteins/bace1) — Beta-secretase

External Links

• [NCBI Gene: 5664](https://www.ncbi.nlm.nih.gov/gene/5664)
• [UniProt: O00287](https://www.uniprot.org/uniprot/O00287)
• [PDB structures](https://www.rcsb.org/search?q=uniprot:O00287)

References

Pathway Diagram

The following diagram shows the key molecular relationships involving PSEN2 Protein (Presenilin-2) discovered through SciDEX knowledge graph analysis: