Caspase-1 Protein

Caspase-1 Protein

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Caspase-1</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Caspase-1 (ICE, Interleukin-1β Converting Enzyme)</td></tr>
<tr><td><strong>Gene</strong></td><td><a href="/entities/casp1-gene">CASP1</a></td></tr>
<tr><td><strong>UniProt ID</strong></td><td><a href="https://www.uniprot.org/uniprot/P29466">P29466</a></td></tr>
<tr><td><strong>PDB IDs</strong></td><td>1ICE, 1BMQ, 1RWK, 2H48, 6CL0</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~45.2 kDa (zymogen); ~20 kDa (p20) + ~10 kDa (p10) active</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Cytoplasm; recruited to inflammasome complexes</td></tr>
<tr><td><strong>Protein Family</strong></td><td>Cysteine-aspartate protease (caspase) family, inflammatory caspase subfamily</td></tr>
<tr><td><strong>EC Number</strong></td><td>3.4.22.36</td></tr>
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<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
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</div>

Overview

Caspase-1 Protein

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Caspase-1</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Caspase-1 (ICE, Interleukin-1β Converting Enzyme)</td></tr>
<tr><td><strong>Gene</strong></td><td><a href="/entities/casp1-gene">CASP1</a></td></tr>
<tr><td><strong>UniProt ID</strong></td><td><a href="https://www.uniprot.org/uniprot/P29466">P29466</a></td></tr>
<tr><td><strong>PDB IDs</strong></td><td>1ICE, 1BMQ, 1RWK, 2H48, 6CL0</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~45.2 kDa (zymogen); ~20 kDa (p20) + ~10 kDa (p10) active</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Cytoplasm; recruited to inflammasome complexes</td></tr>
<tr><td><strong>Protein Family</strong></td><td>Cysteine-aspartate protease (caspase) family, inflammatory caspase subfamily</td></tr>
<tr><td><strong>EC Number</strong></td><td>3.4.22.36</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Overview

Caspase-1 (formerly known as interleukin-1β converting enzyme, ICE) is the founding member of the inflammatory caspase subfamily and a central effector of innate immunity in the central nervous system[@bhatt1992]. Unlike apoptotic caspases (e.g., [caspase-9](/entities/caspases-9-protein), caspase-3), caspase-1 does not directly participate in programmed cell death via the classical apoptotic pathway. Instead, it serves as the proteolytic engine of inflammasome complexes, cleaving pro-IL-1β and pro-IL-18 into their biologically active forms and processing gasdermin D (GSDMD) to trigger pyroptosis — an inflammatory form of regulated cell death[@shi2015].

In the brain, caspase-1 is predominantly expressed in [microglia](/entities/microglia-in-neurodegeneration) and [astrocytes](/cell-types/astrocytes), with induced expression in [neurons](/entities/neurons) under pathological conditions. Its activation is a convergence point for multiple danger signals in neurodegeneration, including amyloid-β aggregates, [α-synuclein](/proteins/alpha-synuclein) fibrils, oxidized mitochondrial DNA, and extracellular ATP signaling through the [P2X7 receptor](/proteins/p2rx7-protein)[@heneka2015]. Chronic caspase-1 activation is now recognized as a key driver of the sustained neuroinflammation observed in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), [ALS](/diseases/amyotrophic-lateral-sclerosis), and [multiple sclerosis](/diseases/multiple-sclerosis)[@voet2019].

Structure

Domain Organization

Caspase-1 is synthesized as a 404-amino-acid zymogen (pro-caspase-1) with the following domain architecture:

• CARD domain (residues 1–91): The caspase activation and recruitment domain mediates homotypic interactions with the CARD of ASC ([apoptosis](/entities/apoptosis)-associated speck-like protein containing a CARD), enabling recruitment to inflammasome complexes
• Large catalytic subunit (p20) (residues 120–297): Contains the active-site cysteine (C285) and histidine (H237) residues that form the catalytic dyad; recognizes the WEHD↓ substrate motif (with preference for Asp at P1)
• Small catalytic subunit (p10) (residues 317–404): Completes the catalytic domain; contributes to substrate binding groove formation
• Interdomain linker (residues 298–316): Proteolytically cleaved during activation; removal releases the p20-p10 heterodimer[@walker1994]

Active Enzyme Assembly

Mature caspase-1 functions as a dimer of p20/p10 heterodimers, forming a (p20/p10)₂ complex. The crystal structure (PDB: 1ICE) reveals a compact globular fold with four β-sheets forming a central core. The two active sites are oriented on the same face of the molecule, with substrate binding grooves defining the strict preference for aspartate at the P1 position[@wilson1994].

Catalytic Mechanism

Caspase-1 employs a cysteine protease mechanism:

The preferred recognition sequence is WEHD↓ (Trp-Glu-His-Asp), distinguishing it from apoptotic caspases which prefer DEVD (caspase-3) or LEHD (caspase-9)[@thornberry1997].

Normal Function in the Nervous System

Cytokine Maturation

The canonical function of caspase-1 is the proteolytic processing of inflammatory cytokine precursors:

• Pro-IL-1β → IL-1β: Caspase-1 cleaves the 31 kDa pro-IL-1β at D116-A117, releasing the 17 kDa mature IL-1β. In the brain, IL-1β at physiological levels regulates synaptic plasticity, sleep, and fever response
• Pro-IL-18 → IL-18: Caspase-1 cleaves pro-IL-18 at D36-Y37. Mature IL-18 modulates IFN-γ production by T cells and NK cells, contributing to CNS immune surveillance[@bhatt1994]

Pyroptosis Execution

Caspase-1 cleaves gasdermin D (GSDMD) at D275, releasing the N-terminal domain (GSDMD-NT) which oligomerizes in the plasma membrane to form 10–20 nm pores. These pores:

• Allow release of mature IL-1β and IL-18 (which lack signal peptides)
• Cause osmotic swelling and cell lysis (pyroptosis)
• Release damage-associated molecular patterns (DAMPs) that amplify inflammation[@ding2016]

Unconventional Protein Secretion

Beyond pyroptosis, caspase-1-generated GSDMD pores serve as conduits for unconventional secretion of leaderless cytoplasmic proteins, representing a regulated secretory pathway independent of the ER-Golgi apparatus[@bhatt2018].

Inflammasome Activation Pathways

NLRP3 Inflammasome (Primary CNS Pathway)

The [NLRP3 inflammasome](/mechanisms/nlrp3-inflammasome) is the most extensively studied caspase-1 activation platform in neurodegeneration:

• K⁺ efflux via [P2X7](/proteins/p2rx7-protein) ATP-gated channels
• Lysosomal rupture from phagocytosed crystals or aggregates
• Mitochondrial dysfunction (oxidized mtDNA, cardiolipin, ROS)
• Ca²⁺ signaling perturbations

Other Inflammasomes

• NLRP1: Activated by anthrax lethal toxin and viral proteases; expressed in neurons
• NLRC4/NAIP: Activated by bacterial flagellin and type III secretion system components
• AIM2: Activated by cytoplasmic double-stranded DNA, including oxidized mitochondrial DNA released during neurodegeneration[@bhatt2016]

Role in Neurodegenerative Disease

Alzheimer's Disease

Caspase-1 activation is a central mechanism linking amyloid pathology to [tau](/proteins/tau) pathology and neurodegeneration:

• Amyloid-β activation: Fibrillar [Aβ](/proteins/amyloid-beta) phagocytosed by [microglia](/cell-types/microglia-neuroinflammation) causes lysosomal rupture → cathepsin B release → NLRP3 activation → caspase-1. The landmark Heneka et al. (2013) study demonstrated that NLRP3⁻/⁻ and caspase-1⁻/⁻ [APP](/entities/app-protein)/PS1 mice have dramatically reduced amyloid burden, rescued spatial memory, and enhanced microglial Aβ phagocytosis[@heneka2013]
• ASC speck propagation: Released ASC specks bind amyloid-β and cross-seed amyloid aggregation, creating a feed-forward loop between inflammasome activation and amyloid pathology[@venegas2017]
• Tau cleavage: Caspase-1 directly cleaves tau at D421, generating a truncated form (Tau-ΔD421) that aggregates more readily and seeds neurofibrillary tangle formation
• Gasdermin D pores in neurons: Neuronal caspase-1 activation produces GSDMD pores that disrupt ionic homeostasis, contributing to excitotoxicity[@bhatt2011]

Parkinson's Disease

• α-Synuclein fibrils: Extracellular α-synuclein aggregates activate microglial NLRP3/caspase-1 pathway, with fibrillar forms being more potent activators than oligomers
• Dopaminergic neuron vulnerability: Caspase-1 inhibition (VX-765) protects against MPTP-induced dopaminergic neuron loss in mice
• [Gut-brain axis](/entities/gut-brain-axis): Intestinal caspase-1 activation by α-synuclein in enteric neurons may initiate the centripetal spread of PD pathology[@gordon2018]

Amyotrophic Lateral Sclerosis

• SOD1 mutant activation: Mutant SOD1 aggregates activate microglial NLRP3/caspase-1, with caspase-1 upregulation detectable at presymptomatic stages in SOD1-G93A mice
• Motor neuron pyroptosis: Caspase-1-dependent GSDMD pore formation in motor neurons may contribute to the rapid degeneration characteristic of ALS
• [TDP-43](/mechanisms/tdp-43-proteinopathy) aggregates: [TDP-43](/proteins/tdp-43-protein) cytoplasmic aggregates activate the caspase-1 pathway in both microglia and neurons[@zhao2015]

Therapeutic Targeting

Caspase-1 Inhibitors

| Compound | Type | Stage | Notes |
|----------|------|-------|-------|
| VX-765 (Belnacasan) | Prodrug → VRT-043198 (active) | Phase II (epilepsy) | Orally bioavailable, [BBB](/entities/blood-brain-barrier)-penetrant; shown neuroprotective in AD and PD mouse models |
| VX-740 (Pralnacasan) | Reversible inhibitor | Phase II (RA, discontinued) | Limited CNS penetration |
| Ac-YVAD-CMK | Irreversible peptide inhibitor | Research tool | Not drug-like |
| z-VAD-FMK | Pan-caspase inhibitor | Research tool | Non-selective |
| MCC950 (CRID3) | NLRP3 inhibitor (indirect) | Phase II (multiple) | Blocks upstream of caspase-1 activation |
| Dapansutrile (OLT1177) | NLRP3 inhibitor | Phase II (gout) | Oral, anti-inflammatory |

VX-765 is the most advanced caspase-1 inhibitor with CNS activity, demonstrating efficacy in APP/PS1 and MPTP mouse models[@flores2018].

Anti-IL-1β Biologics

• Canakinumab (anti-IL-1β monoclonal antibody): Approved for systemic inflammatory diseases; CANTOS trial showed cardiovascular benefit; CNS penetration limited but may modulate peripheral-to-central inflammation
• Anakinra (IL-1 receptor antagonist): Limited BBB penetration but intrathecal administration reduces neuroinflammation in animal models[@dhimolea2010]

Key Interactions

• [NLRP3](/genes/nlrp3): Primary upstream inflammasome sensor in CNS
• ASC (PYCARD): Adaptor protein bridging NLRP3 to caspase-1 via CARD interactions
• [P2X7](/proteins/p2rx7-protein): ATP receptor providing K⁺ efflux signal for NLRP3 activation
• Gasdermin D (GSDMD): Pore-forming effector cleaved by caspase-1
• Pro-IL-1β / Pro-IL-18: Cytokine substrates
• [Caspase-8](/entities/caspases-8-protein): Non-canonical inflammasome pathway; can substitute for caspase-1 in some contexts
• [NEK7](/genes/nek7): Essential cofactor for NLRP3 oligomerization upstream of caspase-1 activation

See Also

• [NLRP3 Inflammasome](/mechanisms/nlrp3-inflammasome)
• [P2RX7 Protein](/proteins/p2rx7-protein)
• [Caspase-9 Protein](/entities/caspases-9-protein)
• [Neuroinflammation](/mechanisms/neuroinflammation)
• [Pyroptosis](/mechanisms/pyroptosis)
• [Gasdermin D](/proteins/gsdmd-protein)

External Links

• [UniProt: P29466](https://www.uniprot.org/uniprot/P29466)
• [NCBI Gene: CASP1](https://www.ncbi.nlm.nih.gov/gene/834)
• [PDB: 1ICE](https://www.rcsb.org/structure/1ICE)
• [OMIM: 147678](https://www.omim.org/entry/147678)

References