Nicastrin (NCSTN Protein)

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Nicastrin (NCSTN Protein)

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Nicastrin (NCSTN Protein)

Introduction

Nicastrin (encoded by the [NCSTN gene](/genes/ncstn)) is an essential subunit of the [γ-secretase](/entities/gamma-secretase) complex that cleaves [amyloid precursor protein (APP)](/genes/app) and [Notch](/genes/notch1) receptors. As a gatekeeper for γ-secretase substrate access, nicastrin is central to [amyloid-β](/proteins/amyloid-beta-protein) production in [Alzheimer's disease](/diseases/alzheimers-disease).

Overview

Nicastrin is a type I transmembrane glycoprotein of ~130 kDa that serves as the substrate receptor of the γ-secretase complex[1]. The γ-secretase complex — composed of [presenilin-1](/genes/psen1) or [presenilin-2](/genes/psen2) (catalytic subunit), nicastrin, APH-1, and PEN-2 — is an intramembrane aspartyl protease essential for processing over 90 type I transmembrane substrates[2]. Nicastrin recognizes the N-terminus of substrate ectodomains after ectodomain shedding, gating substrate access to the presenilin active site. [@strooper2003]

<div class="infobox infobox-protein"> [@xie2014]

| | | [@selkoe2016]
|---|---| [@wang2010]
| Protein Name | Nicastrin |
| Gene | [NCSTN](/genes/ncstn) |
| UniProt ID | [Q92542](https://www.uniprot.org/uniprot/Q92542) |
| Molecular Weight | ~78 kDa (predicted), ~130 kDa (mature, glycosylated) |
| Length | 709 amino acids |
| Subcellular Localization | Plasma membrane, endosomes, Golgi |
| Function | γ-secretase substrate receptor |

</div>

Structure

Domain Architecture

...

Nicastrin (NCSTN Protein)

Introduction

Nicastrin (encoded by the [NCSTN gene](/genes/ncstn)) is an essential subunit of the [γ-secretase](/entities/gamma-secretase) complex that cleaves [amyloid precursor protein (APP)](/genes/app) and [Notch](/genes/notch1) receptors. As a gatekeeper for γ-secretase substrate access, nicastrin is central to [amyloid-β](/proteins/amyloid-beta-protein) production in [Alzheimer's disease](/diseases/alzheimers-disease).

Overview

Nicastrin is a type I transmembrane glycoprotein of ~130 kDa that serves as the substrate receptor of the γ-secretase complex[1]. The γ-secretase complex — composed of [presenilin-1](/genes/psen1) or [presenilin-2](/genes/psen2) (catalytic subunit), nicastrin, APH-1, and PEN-2 — is an intramembrane aspartyl protease essential for processing over 90 type I transmembrane substrates[2]. Nicastrin recognizes the N-terminus of substrate ectodomains after ectodomain shedding, gating substrate access to the presenilin active site. [@strooper2003]

<div class="infobox infobox-protein"> [@xie2014]

| | | [@selkoe2016]
|---|---| [@wang2010]
| Protein Name | Nicastrin |
| Gene | [NCSTN](/genes/ncstn) |
| UniProt ID | [Q92542](https://www.uniprot.org/uniprot/Q92542) |
| Molecular Weight | ~78 kDa (predicted), ~130 kDa (mature, glycosylated) |
| Length | 709 amino acids |
| Subcellular Localization | Plasma membrane, endosomes, Golgi |
| Function | γ-secretase substrate receptor |

</div>

Structure

Domain Architecture

Nicastrin has a large ectodomain and a single transmembrane pass[3]:

Large extracellular ectodomain (~670 aa): Aminopeptidase-like fold (catalytically inactive); contains the substrate-binding site
DAP domain: Peptidase-like domain that recognizes free N-termini of γ-secretase substrates
Lid domain: Covers the active site region; opens to admit substrates
Single transmembrane helix: Anchors nicastrin in the membrane; interacts with APH-1
Short cytoplasmic tail (~20 aa): Contains ER retention/retrieval signals
N-glycosylation: 16 potential N-glycosylation sites; heavy glycosylation critical for maturation and surface expression

γ-Secretase Complex Assembly

The four subunits assemble in a defined order in the ER[2]:

APH-1 + Nicastrin: Form the initial scaffold

+ Presenilin ([PSEN1](/entities/psen1)/2): Associates with the APH-1-Nicastrin dimer

+ PEN-2: Triggers presenilin endoproteolysis and complex activation

Mature complex: Traffics from ER → Golgi → plasma membrane/endosomes

Function

Substrate Gating

Nicastrin's ectodomain functions as the substrate receptor for γ-secretase[1]:

N-terminus recognition: Nicastrin's Glu333 (DAP domain) recognizes the free N-terminal stub of substrates after ectodomain shedding (by α- or β-secretase)
Size filter: Ectodomain acts as a molecular ruler — only substrates with short (<50 aa) residual ectodomains can access the presenilin active site
No enzymatic activity: Despite structural similarity to aminopeptidases, nicastrin has no catalytic activity

Key Substrates Gated by Nicastrin

| Substrate | Sheddase | γ-Secretase Product | Disease Relevance |
|-----------|----------|---------------------|-------------------|
| [APP](/genes/app) | [β-secretase](/entities/bace1) ([BACE1](/genes/bace1)) | [Aβ40/Aβ42](/proteins/amyloid-beta-protein) | [Alzheimer's disease](/diseases/alzheimers-disease) |
| [APP](/genes/app) | α-secretase ([ADAM10](/genes/adam10)) | p3 (non-amyloidogenic) | Non-pathogenic |
| [Notch1-4](/genes/notch1) | ADAM10/TACE | NICD (transcription factor) | Development, cancer |
| N-cadherin | ADAM10 | CTF2 | Synaptic signaling |
| ErbB4 | ADAM17 | ICD | Neuregulin signaling |

Amyloid-β Production

Nicastrin is required for γ-secretase cleavage of APP into Aβ peptides[4]:

After β-secretase cleavage, APP C-terminal fragment (C99) has a free N-terminus recognized by nicastrin
Nicastrin presents C99 to presenilin's intramembrane active site
Sequential cleavage produces [Aβ40](/proteins/amyloid-beta) (predominant) and Aβ42 (pathogenic, aggregation-prone)
Nicastrin dysfunction alters the Aβ40/Aβ42 ratio

Role in Neurodegeneration

Alzheimer's Disease

Nicastrin modulates AD pathogenesis through its role in Aβ production[4]:

Nicastrin levels correlate with γ-secretase activity and Aβ generation
Some NCSTN variants modify AD risk, though less prominent than [PSEN1](/genes/psen1)/PSEN2 mutations
Nicastrin is a potential therapeutic target for modulating γ-secretase substrate specificity

Familial Acne Inversa (Hidradenitis Suppurativa)

Heterozygous loss-of-function NCSTN mutations cause familial acne inversa[5]:

Loss of Notch signaling in skin follicular epithelium
Hair follicle dysfunction → inflammation → abscess formation
Demonstrates that partial γ-secretase loss affects Notch signaling before APP processing

Therapeutic Considerations

γ-Secretase inhibitors (GSIs): Non-selective GSIs failed in AD trials due to Notch toxicity (diarrhea, skin cancer risk)
γ-Secretase modulators (GSMs): Shift cleavage to produce shorter, less pathogenic Aβ38 without affecting Notch — nicastrin structure informs GSM design
Substrate-selective inhibitors: Targeting nicastrin's substrate recognition to selectively block APP processing while sparing Notch

Protein Interactions

| Interactor | Type | Function |
|-----------|------|----------|
| [Presenilin-1](/genes/psen1) | Complex subunit | Catalytic subunit of γ-secretase |
| [Presenilin-2](/genes/psen2) | Complex subunit | Alternative catalytic subunit |
| APH-1A/1B | Complex subunit | Scaffolding subunit |
| PEN-2 | Complex subunit | Presenilin endoproteolysis trigger |
| [APP C99](/genes/app) | Substrate | [Amyloid precursor protein](/entities/app-protein) C-terminal fragment |
| Notch receptors | Substrate | Developmental signaling receptors |

External Links

[Nicastrin - UniProt](https://www.uniprot.org/uniprot/Q92542)
[NCSTN - NCBI Gene](https://www.ncbi.nlm.nih.gov/gene/23385)
[γ-Secretase - PDB](https://www.rcsb.org/structure/5A63)

References

[Shah S et al., Nicastrin functions as a gamma-secretase-substrate receptor (2005) (2005)](https://doi.org/10.1016/j.cell.2005.05.036)

[Unknown, De Strooper B, Aph-1, Pen-2, and Nicastrin with Presenilin generate an active gamma-secretase complex (2003) (2003)](https://doi.org/10.1016/S0896-6273(03)

[Xie T et al., Crystal structure of the gamma-secretase component nicastrin (2014) (2014)](https://doi.org/10.1073/pnas.1414837111)

[Unknown, Selkoe DJ & Hardy J, The amyloid hypothesis of Alzheimer's disease at 25 years (2016) (2016)](https://doi.org/10.15252/embj.201695957)

[Wang B et al., Gamma-secretase gene mutations in familial acne inversa (2010) (2010)](https://doi.org/10.1126/science.1196154)

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Related Entities

NCSTNPROTEIN

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slug	proteins-ncstn-protein
kg_node_id	NCSTNPROTEIN
entity_type	protein
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-78b1f28c362e
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'proteins-ncstn-protein'}
_schema_version	1

📊 Evidence Profile

Evidence Balance

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Certainty

45%

Debates

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Outgoing

11

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📗 Cite This Artifact

Nicastrin (NCSTN Protein)

Nicastrin (NCSTN Protein)

Introduction

Overview

Structure

Domain Architecture

Nicastrin (NCSTN Protein)

Introduction

Overview

Structure

Domain Architecture

γ-Secretase Complex Assembly

Function

Substrate Gating

Key Substrates Gated by Nicastrin

Amyloid-β Production

Role in Neurodegeneration

Alzheimer's Disease

Familial Acne Inversa (Hidradenitis Suppurativa)

Therapeutic Considerations

Protein Interactions

See Also

External Links

References

💬 Discussion