SMAC Gene
Overview
Mermaid diagram (expand to render)
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">SMAC Gene</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>SMAC / DIABLO</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Second Mitochondria-Derived Activator of Caspases</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>12p12.31</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>56616</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>605704</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000184047</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q9NR28</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>239 amino acids (precursor), 184 amino acids (mature)</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>26.9 kDa (precursor), 22.5 kDa (mature)</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/ataxia" style="color:#ef9a9a">Ataxia</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a>, <a href="/wiki/glioblastoma" style="color:#ef9a9a">Glioblastoma</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">55 edges</a></td>
</tr>
</table>
Smac Gene plays an important role in the study of neurodegenerative diseases. This page provides comprehensive information about this topic, including its mechanisms, significance in disease processes, and therapeutic implications.
Introduction
SMAC (Second Mitochondria-Derived Activator of Caspases), also known as DIABLO (Direct IAP Binding protein with Low pI), is a pro-apoptotic mitochondrial protein that plays a central role in programmed cell death. SMAC is released from mitochondria during [apoptosis](/entities/apoptosis) and antagonizes Inhibitor of Apoptosis Proteins (IAPs), enabling caspase activation and efficient cell death. Dysregulated SMAC-mediated apoptosis contributes to neurodegeneration in Alzheimer's Disease (AD), Parkinson's Disease (PD), Stroke, and traumatic brain injury. The gene is located on chromosome 12p12.31 and encodes a 239-amino acid precursor protein that is processed to a 29 kDa mature form. [@verhagen2000]
Protein Structure
SMAC has a distinctive structure optimized for its pro-apoptotic function:
- N-terminal mitochondrial targeting sequence (residues 1-55): Directs protein to mitochondria
- Processing site (Ala55): Cleaved by mitochondrial processing peptidase to generate mature form
- IAP-binding motif (IBM) (residues 56-70): Critical for IAP antagonism
- Dimerization domain (residues 150-239): Forms functional dimers required for activity
- Extended dimer interface: Stabilizes the active dimeric form
The mature SMAC forms a homodimer that adopts a barrel-like structure.
Normal Function
Apoptosis Regulation
SMAC functions as a key amplifier of the intrinsic apoptotic pathway:
Mitochondrial release: Upon apoptotic stimuli, SMAC is released from mitochondrial intermembrane space
IAP binding: SMAC dimers bind to IAP proteins (XIAP, c-IAP1, c-IAP2)
Caspase activation: By neutralizing IAPs, SMAC enables caspase-9 and caspase-3 activation
Apoptosome cooperation: SMAC synergizes with Apaf-1/apoptosome functionCellular Roles
- Apoptosis amplification: Enhances caspase activation cascade
- IAP neutralization: Prevents IAP-mediated caspase inhibition
- Stress response: Mediates cell death in response to DNA damage, oxidative stress
- Development: Essential for proper embryonic development
Non-Apoptotic Functions
- [Autophagy](/entities/autophagy) regulation: May influence autophagic processes
- [NF-κB](/entities/nf-kb) signaling: Can modulate survival pathways
Role in Neurodegeneration
Alzheimer's Disease
SMAC plays a complex role in AD pathogenesis:
- Elevated SMAC levels in AD brain tissue (PMID:14586011)
- Enhanced apoptosis in vulnerable neuronal populations
- [Amyloid-beta](/proteins/amyloid-beta) induced SMAC release: Aβ triggers mitochondrial permeabilization
- [Tau](/proteins/tau) pathology: May amplify tau-induced neuronal death
- Contributes to synaptic loss and neuronal dysfunction
Parkinson's Disease
- Increased SMAC in substantia nigra of PD patients
- Mitochondrial dysfunction leads to SMAC release in dopaminergic [neurons](/entities/neurons)
- [α-synuclein](/proteins/alpha-synuclein) toxicity involves SMAC-mediated apoptosis
- May contribute to progressive dopaminergic neuron loss
Stroke and Traumatic Brain Injury
- Secondary injury involves SMAC release and neuronal apoptosis
- Neuroprotective strategies targeting SMAC release are being explored
- Ischemia-reperfusion triggers SMAC-mediated cell death
Amyotrophic Lateral Sclerosis
- Motor neuron apoptosis involves SMAC pathway
- SOD1 mutations may sensitize neurons to SMAC-mediated death
Huntington's Disease
- Mutant [huntingtin](/proteins/huntingtin) induces SMAC release
- Contributes to striatal neuron degeneration
Interaction Network
SMAC interacts with:
- XIAP: Primary target, strongest binding
- c-IAP1: E3 ligase, can ubiquitinate SMAC
- c-IAP2: Overlapping function with c-IAP1
- ML-IAP/BIRC7: High-affinity SMAC binding
- Apaf-1: Apoptosome component
- Caspase-9: Primary effector caspase
- Caspase-3: Executioner caspase
- Bcl-2 family proteins: Regulated by Bcl-2/Bcl-xL
Therapeutic Implications
SMAC Mimetics (Smac Mimetics)
- Birinapant: Clinical-stage SMAC mimetic
- LCL161: In clinical trials for cancer
- AT406: Potent IAP antagonist
- These compounds sensitize cancer cells to apoptosis
Neuroprotective Strategies
- Inhibiting SMAC release: Protecting mitochondrial integrity
- IAP stabilization: XIAP overexpression may protect neurons
- Caspase inhibition: Downstream blockade of apoptosis
See Also
- [Apoptosis Pathways](/mechanisms/apoptosis)
- [Mitochondrial Apoptosis](/mechanisms/mitochondrial-apoptosis)
- [IAP Proteins](/proteins/iap-proteins)
- [XIAP Protein](/proteins/xiap-protein)
- [Caspase Activation](/mechanisms/caspase-cascade)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Stroke](/diseases/stroke)
- [Traumatic Brain Injury](/diseases/traumatic-brain-injury)
Overview
Smac Gene plays an important role in the study of neurodegenerative diseases. This page provides comprehensive information about this topic, including its mechanisms, significance in disease processes, and therapeutic implications.
Background
The study of Smac Gene 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.
External Links
- [NCBI Gene: SMAC](https://www.ncbi.nlm.nih.gov/gene/56616)
- [UniProt: Q9NR28](https://www.uniprot.org/uniprot/Q9NR28)
- [Ensembl: ENSG00000184047](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000184047)
- [GeneCards: DIABLO](https://www.genecards.org/cgi-bin/carddisp.pl?gene=DIABLO)
References
[Chai J, et al, (2000) (2000)](https://pubmed.ncbi.nlm.nih.gov/10853944/)
[Verhagen AM, et al, (2000) (2000)](https://pubmed.ncbi.nlm.nih.gov/10853945/)
[Potts MB, et al, (2003) (2003)](https://pubmed.ncbi.nlm.nih.gov/14586011/)
[Vischioni E, et al, (2006) (2006)](https://pubmed.ncbi.nlm.nih.gov/16628479/)
[Zhou J, et al, (2010) (2010)](https://pubmed.ncbi.nlm.nih.gov/20606688/)
[Srinivasula SM, et al, (2000) (2000)](https://pubmed.ncbi.nlm.nih.gov/10878809/)Pathway Diagram
The following diagram shows the key molecular relationships involving SMAC Gene discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)