| BH3 Interacting Domain Death Agonist | |
|---|---|
| Gene Symbol | BID |
| Full Name | BH3 Interacting Domain Death Agonist |
| Chromosomal Location | 22q11.21 |
| NCBI Gene ID | 637 |
| Ensembl ID | ENSG00000105619 |
| UniProt ID | P55957 |
| OMIM ID | 603678 |
| Protein Length | 195 amino acids |
| Protein Family | BCL2 family, BH3-only proteins |
| Aliases | tBID, truncated BID |
| Associated Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), Stroke, [Traumatic Brain Injury](/diseases/traumatic-brain-injury), ALS |
BID (BH3 Interacting Domain Death Agonist) is a pro-apoptotic BCL2 family protein that serves as a critical molecular link between the extrinsic (death receptor) and intrinsic (mitochondrial) apoptosis pathways. As a "BH3-only" protein, BID contains a single BH3 domain that enables it to interact with both pro-survival BCL2 proteins (BCL2, BCL2L1, MCL1) and the executioner proteins BAX and BAK1.
Upon cleavage by caspase-8, the resulting truncated form (tBID) translocates to mitochondria where it directly activates BAX, promoting cytochrome c release and amplification of the apoptotic cascade. In neurons, BID-mediated apoptosis contributes to neurodegenerative processes following stroke, traumatic brain injury, and chronic neurodegenerative diseases including Alzheimer's disease and Parkinson's disease [1][2].
BID possesses a distinct structural organization:
The BH3 domain is the functional core of BID, mediating:
Full-length BID (flBID) is a relatively inactive cytosolic protein. Activation occurs through proteolytic cleavage [1:1][3]:
BID Activation Cascade
1. Death Receptor Activation (Fas, TRAIL-R, TNFR1)
│
▼
2. Caspase-8 Activation
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3. BID Cleavage at D75/D81
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4. tBID Formation (truncated BID)
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5. tBID Mitochondrial Translocation
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6. BAX/BAK1 Activation → MOMP → Cytochrome c Release
As a BH3-only protein, BID exhibits dual functionality:
Sensitizer function: Sequestration of pro-survival BCL2 proteins
Direct activator function: Direct interaction with BAX/BAK1
BID contributes to AD pathogenesis through multiple mechanisms [5]:
The balance between pro-apoptotic BID and anti-apoptotic BCL2 determines neuronal fate in AD.
In PD, BID mediates dopaminergic neuron death through [6]:
BID is critically involved in ischemic neuronal death [7][8]:
Following TBI [8:1]:
BID serves as the molecular bridge between death receptor signaling and mitochondrial apoptosis [9]:
Death Receptor Pathway Mitochondrial Pathway
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
FasL/TRAIL/TNF-α │
│ │
▼ ▼
Fas/TRAIL-R/TNFR1 BAX/BAK1
│ │
▼ ▼
FADD → Caspase-8 tBID → Activation
│ │
▼ ▼
BID cleavage MOMP
│ │
└─────── tBID ───────────┘
│
▼
Cytochrome c release
│
▼
Apoptosome formation
│
▼
Caspase-9 → Caspase-3/7
│
▼
Cell death
Positive regulators:
Negative regulators:
BID is expressed throughout the central nervous system:
| Region | Expression Level | Notes |
|---|---|---|
| Cortex | High | Pyramidal neurons |
| Hippocampus | High | CA1, CA3 neurons |
| Substantia nigra | Moderate | Dopaminergic neurons |
| Cerebellum | Moderate | Purkinje cells |
| Spinal cord | Moderate | Motor neurons |
Caspase-8 inhibitors [10]
BH3 mimetics
Gene therapy approaches
| Partner | Interaction Type | Function |
|---|---|---|
| Caspase-8 | Substrate | Proteolytic activation |
| BAX | Direct activator | Pore formation |
| BAK1 | Direct activator | Pore formation |
| BCL2 | Binding | Sequestration |
| BCL2L1 | Binding | Sequestration |
| MCL1 | Binding | Sequestration |
| FADD | Co-factor | Death receptor signaling |
| TNFRSF10B | Pathway | Death receptor activation |
BID activation status serves as: