IP₃ Receptor Protein

IP₃ Receptor Protein

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2">IP₃ Receptor (ITPR1)</th></tr>
<tr><td>Gene</td><td>[ITPR1](/genes/itpr1)</td></tr>
<tr><td>UniProt ID</td><td>[Q14643](https://www.uniprot.org/uniprot/Q14643)</td></tr>
<tr><td>PDB</td><td>6MU2, 6MU3, 7L9Z, 8EAR</td></tr>
<tr><td>Molecular Weight</td><td>314 kDa (monomer), ~1.2 MDa tetramer</td></tr>
<tr><td>Localization</td><td>Endoplasmic reticulum membrane</td></tr>
<tr><td>Family</td><td>Intracellular calcium release channel family</td></tr>
<tr><td>Disease</td><td>SCA15/16, SCA29, AD, ALS</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">3 edges</a></td>
</tr>
</table>
</div>

Overview

The inositol 1,4,5-trisphosphate receptor (IP₃R) is a large calcium release channel located on the endoplasmic reticulum (ER) membrane. IP₃Rs mediate calcium release from ER stores in response to IP₃ generated by phospholipase C activation. IP₃R dysfunction contributes to calcium dyshomeostasis in Alzheimer's disease, ALS, and spinocerebellar ataxias.

Structure

IP₃R is a massive tetrameric channel (~1.2 MDa) with each subunit containing:

• N-terminal IP₃-binding domain: High-affinity IP₃ binding (suppressor domain)
• Large regulatory domain: Contains regulatory sites for Ca²⁺, ATP, and modulators
• Central modulatory domain: Includes IRAG (IP₃R-associated protein) binding
• Six transmembrane domains (TM1-6): Form the ion channel pore
• C-terminal gatekeeper domain: Channel gating regulation

IP₃ Receptor Protein

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2">IP₃ Receptor (ITPR1)</th></tr>
<tr><td>Gene</td><td>[ITPR1](/genes/itpr1)</td></tr>
<tr><td>UniProt ID</td><td>[Q14643](https://www.uniprot.org/uniprot/Q14643)</td></tr>
<tr><td>PDB</td><td>6MU2, 6MU3, 7L9Z, 8EAR</td></tr>
<tr><td>Molecular Weight</td><td>314 kDa (monomer), ~1.2 MDa tetramer</td></tr>
<tr><td>Localization</td><td>Endoplasmic reticulum membrane</td></tr>
<tr><td>Family</td><td>Intracellular calcium release channel family</td></tr>
<tr><td>Disease</td><td>SCA15/16, SCA29, AD, ALS</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">3 edges</a></td>
</tr>
</table>
</div>

Overview

The inositol 1,4,5-trisphosphate receptor (IP₃R) is a large calcium release channel located on the endoplasmic reticulum (ER) membrane. IP₃Rs mediate calcium release from ER stores in response to IP₃ generated by phospholipase C activation. IP₃R dysfunction contributes to calcium dyshomeostasis in Alzheimer's disease, ALS, and spinocerebellar ataxias.

Structure

IP₃R is a massive tetrameric channel (~1.2 MDa) with each subunit containing:

• N-terminal IP₃-binding domain: High-affinity IP₃ binding (suppressor domain)
• Large regulatory domain: Contains regulatory sites for Ca²⁺, ATP, and modulators
• Central modulatory domain: Includes IRAG (IP₃R-associated protein) binding
• Six transmembrane domains (TM1-6): Form the ion channel pore
• C-terminal gatekeeper domain: Channel gating regulation

Normal Function

IP₃Rs have critical roles in calcium signaling:

Three IP₃R isoforms exist with distinct properties:

• IP₃R1: Brain, cerebellum (highest expression)
• IP₃R2: Glial cells, liver, cardiac muscle
• IP₃R3: Widespread, secretory cells

Role in Neurodegeneration

Alzheimer's Disease

IP₃R dysfunction contributes to AD pathogenesis[@leissring2001]:

Mechanisms of enhanced IP₃R signaling in AD:

• Presenilin mutations increase ER Ca²⁺ stores
• Aβ oligomers activate PLC pathway
• Reduced ER calcium buffering
• MAM contact site proliferation

Spinocerebellar Ataxia (SCA15/16, SCA29)

ITPR1 mutations cause several cerebellar ataxias:

SCA15/16: Deletions and missense mutations

• Slowly progressive ataxia
• Cerebellar vermis atrophy
• Loss of IP₃R function

• Congenital non-progressive ataxia
• Cerebellar hypoplasia
• Gain-of-function or dominant-negative effects[@iwaki2008]

ALS

IP₃R involvement in motor neuron disease:

• SOD1 interaction: Mutant SOD1 affects ER calcium homeostasis
• [TDP-43](/mechanisms/tdp-43-proteinopathy): Alters IP₃R expression
• Excitotoxicity: Excessive Ca²⁺ release contributes to motor neuron death

Huntington's Disease

• mHtt enhances IP₃R sensitivity
• Increased ER Ca²⁺ release
• Contributes to mitochondrial dysfunction

Therapeutic Targeting

| Strategy | Mechanism | Status |
|----------|-----------|--------|
| 2-APB | IP₃R inhibitor (non-specific) | Research tool |
| Xestospongin C | IP₃R inhibitor | Research tool |
| Dantrolene | RyR inhibitor (cross-reactivity) | Clinical (malignant hyperthermia) |
| Calcium stabilizers | Reduce ER-mito transfer | Preclinical |
| Dantrolene derivatives | Improved specificity | Preclinical |

See Also

• [Ryanodine Receptor - Related ER Ca²⁺ channel](/entities/ryanodine-receptor)
• [SERCA - ER Ca²⁺ pump](/proteins/serca)
• [MCU - Mitochondrial Ca²⁺ uniporter](/entities/mitochondria)
• Calcium Dyshomeostasis
• [ER Stress](/mechanisms/er-stress-pathway)