CAPN1 Protein

CAPN1 Protein

Introduction

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">CAPN1 Protein</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>CAPN1</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>CAPN1</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Protein</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/?query=CAPN1" target="_blank">Search UniProt</a></td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/depression" style="color:#ef9a9a">Depression</a>, <a href="/wiki/inflammation" style="color:#ef9a9a">Inflammation</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodegeneration</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">32 edges</a></td>
</tr>
</table>

Capn1 Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Gene: [CAPN1](/proteins/capn1-protein) [@liu2008] UniProt: P07384 [@baudry2013] Molecular Weight: ~82 kDa (catalytic subunit) [@yamashima2019] Subcellular Localization: Cytosol, membrane-associated [@wang2018] Protein Family: Calpain family, cysteine proteases [@czogalla2019]

Overview

CAPN1 Protein

Introduction

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">CAPN1 Protein</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>CAPN1</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>CAPN1</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Protein</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/?query=CAPN1" target="_blank">Search UniProt</a></td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/depression" style="color:#ef9a9a">Depression</a>, <a href="/wiki/inflammation" style="color:#ef9a9a">Inflammation</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodegeneration</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">32 edges</a></td>
</tr>
</table>

Capn1 Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Gene: [CAPN1](/proteins/capn1-protein) [@liu2008] UniProt: P07384 [@baudry2013] Molecular Weight: ~82 kDa (catalytic subunit) [@yamashima2019] Subcellular Localization: Cytosol, membrane-associated [@wang2018] Protein Family: Calpain family, cysteine proteases [@czogalla2019]

Overview

CAPN1 (Calpain 1), also known as μ-calpain or μ-calcium-activated neutral protease (μCANP), is a calcium-dependent cysteine protease that mediates limited proteolysis of various substrates. Calpain 1 is heterodimeric, consisting of a catalytic large subunit (CAPN1, ~80 kDa) and a regulatory small subunit (CAPNS1, ~28 kDa). The protease is ubiquitously expressed and plays critical roles in both normal cellular processes including signal transduction, cell cycle progression, and synaptic plasticity, as well as pathological processes including [apoptosis](/entities/apoptosis) and neurodegeneration. CAPN1 is activated by micromolar calcium concentrations and requires calmodulin for full activity. Unlike calpain 2 (m-calpain), calpain 1 is activated at lower calcium concentrations, making it particularly relevant in physiological signaling. [@ray2014]

Protein Structure

Calpain 1 is a heterodimer composed of: [@huang2001]

Large Subunit (CAPN1, ~80 kDa)

• N-terminal catalytic domain (PC1) with cysteine protease active site
• penta-EF-hand (PEF) domains (PC2) for calcium binding
• C-terminal hydrophobic domain for membrane association

Small Subunit (CAPNS1, ~28 kDa)

• Glycine-rich hydrophobic domain
• PEF domain for dimerization with large subunit

• Active site cysteine (C105)
• Calcium-binding EF-hand motifs
• Autolysis site for activation

Molecular Function

Proteolytic Activity

• Cleaves after specific sequences, not random degradation
• Targets cytoskeletal proteins, signaling molecules, transcription factors
• Regulates protein function through controlled cleavage

Substrate Specificity

• Spectrin (membrane cytoskeletal protein)
• [Tau](/proteins/tau) (microtubule-associated protein)
• Amyloid precursor protein ([APP](/entities/app-protein))
• p35/p39 ([CDK5](/proteins/cdk5-protein) regulatory subunits)
• [NMDA](/entities/nmda-receptor) receptor subunits
• Synaptic proteins (SNAP-25, synaptotagmin)

Calcium Regulation

• Basal activity very low in absence of calcium
• Calcium binding induces conformational change
• Autolysis at ~1 μM Ca²⁺ activates the protease
• Calmodulin binding enhances activation

Role in Neurodegeneration

Alzheimer's Disease

• Overactivation by [Aβ](/proteins/amyloid-beta) oligomers leads to synaptic damage
• Cleaves [tau](/proteins/tau), generating toxic fragments
• Mediates Aβ-induced neuronal apoptosis
• Contributes to cytoskeletal degradation
• Calpain-[cdk5](/proteins/cdk5-protein) pathway dysregulation

Parkinson's Disease

• Activated by dopaminergic neuron stress
• Cleaves [alpha-synuclein](/mechanisms/alpha-synuclein), potentially promoting aggregation
• Mediates mitochondrial dysfunction-induced cell death
• Contributes to Lewy body formation

Amyotrophic Lateral Sclerosis (ALS)

• Activated in motor [neurons](/entities/neurons) by excitotoxicity
• Cleaves mutant SOD1, generating toxic fragments
• Mediates excitotoxic neuronal death
• Contributes to cytoskeletal disruption

Stroke and Traumatic Brain Injury

• Rapidly activated following ischemia
• Mediates excitotoxic cell death
• Contributes to blood-brain barrier breakdown
• Target for neuroprotective therapy

Huntington's Disease

• Calpain activation by mutant [huntingtin](/proteins/huntingtin-protein)
• Generates toxic [huntingtin](/genes/htt) fragments
• Contributes to transcriptional dysregulation

Expression Pattern

CAPN1 is widely expressed in:

• Cerebral [cortex](/brain-regions/cortex) (pyramidal neurons)
• [Hippocampus](/brain-regions/hippocampus) (all regions)
• Cerebellum (Purkinje cells)
• Basal ganglia
• Spinal cord motor neurons

Therapeutic Implications

Inhibitors

• Calpain inhibitors: Leupeptin, ALLN, MDL-28170
• Calpain-specific inhibitors: Calpeptin, PD150606
• Endogenous inhibitor: Calpastatin

Clinical Approaches

• [Blood-brain barrier](/entities/blood-brain-barrier) penetrating inhibitors in development
• Targeting calpain-10 for neurodegeneration
• Gene therapy approaches

Research Directions

• Biomarkers of calpain activation (spectrin breakdown products)
• Neuroprotective strategies using calpain inhibition

Animal Models

• Capn1 knockout mice: Viable but with defects in platelet function
• Transgenic overexpression models: Reveal neuronal vulnerability
• Conditional knockouts: Tissue-specific functions

Background

The study of Capn1 Protein has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

See Also

• [CAPN1 Gene](/genes/capn1)
• Calpain System
• [Calcium Signaling](/mechanisms/calcium-signaling)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)