Caspase 9 is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Caspase-9 is encoded by the CASP9 gene. It is a Caspase family, initiator caspases involved in caspase-9 is the initiator caspase of the intrinsic apoptotic pathway. it is activated by the apopto...
| Caspase-9 |
|---|
| Protein Name | Caspase-9 |
| Gene | CASP9 |
| UniProt ID | P55211 |
| PDB ID(s) | 1JXQ, 1KZX, 1KZY, 2J9O, 3MS3, 3MS4, 4JXU |
| Molecular Weight | 46.6 kDa |
| Subcellular Localization | Mitochondria, Cytoplasm |
| Protein Family | Caspase family, initiator caspases |
Caspase-9 is synthesized as an inactive proenzyme (46 kDa) with an N-terminal prodomain. Upon activation, it forms a tetramer with two catalytic subunits.
Caspase-9 is the initiator caspase of the intrinsic apoptotic pathway. It is activated by the apoptosome (Apaf-1 + cytochrome c) and then cleaves and activates executioner caspases-3, -6, and -7. Caspase-9 activity is regulated by Bcl-2 family proteins and inhibitor of apoptosis proteins (IAPs).
Mitochondrial dysfunction leads to cytochrome c release and apoptosome activation, triggering caspase-9 cascade.
Caspase-9 is activated in dopaminergic neurons following mitochondrial Complex I inhibition and PINK1/Parkin pathway dysfunction.
Ischemic injury triggers mitochondrial permeabilization and caspase-9 mediated neuronal death.
Secondary injury involves mitochondrial dysfunction and caspase-9 activation.
Caspase-9 specific inhibitors (LEHD-FMK) are being studied for neuroprotection in stroke and traumatic brain injury.
Caspase-9 is activated through the intrinsic (mitochondrial) apoptotic pathway:
- Mitochondrial outer membrane permeabilization (MOMP): Triggered by pro-apoptotic Bcl-2 proteins (Bax, Bak)
- Cytochrome c release: Binds to Apaf-1 in cytoplasm
- Apoptosome formation: Cytochrome c + Apaf-1 + dATP/ATP form the apoptosome
- Caspase-9 recruitment: Pro-caspase-9 binds to apoptosome via CARD domains
- Autoactivation: Pro-caspase-9 undergoes conformational change and auto-cleavage
- Executioner caspase activation: Active caspase-9 cleaves and activates caspases-3, -6, -7
- N-terminal CARD domain: Protein-protein interactions with Apaf-1
- Prodomain: ~140 amino acids
- Catalytic subunits: Large (p37) and small (p12) subunits after cleavage
- Active tetramer: Two catalytic dimers
Caspase-9 is regulated by:
- IAPs (Inhibitor of Apoptosis Proteins): XIAP directly inhibits caspase-9
- Bcl-2 family: Anti-apoptotic proteins (Bcl-2, Bcl-xL) prevent cytochrome c release
- Phosphorylation: Akt phosphorylates caspase-9 at Ser196, inhibiting activity
- Alternative splicing: Caspase-9L (long isoform) has different activity
Caspase-9 activation varies across brain regions:
- High susceptibility: Hippocampal CA1 neurons, cortical layer 5 pyramidal neurons
- Moderate: Dopaminergic neurons in substantia nigra
- Lower: Cerebellar neurons
- Caspase-9 knockout mice: Embryonic lethal (defects in brain development)
- Conditional knockout in neurons: Protected from some forms of excitotoxicity
- Neuronal caspase-9 activation reporters
- Fluorescent caspase-9 substrates for in vivo imaging
- LEHD-FMK: Irreversible caspase-9 inhibitor
- Z-LEHD-FMK: Cell-permeable inhibitor
- Small molecule inhibitors: Under development for stroke and TBI
- IAP antagonists (Smac mimetics): Sensitize cells to apoptosis
- Bcl-2 antagonists: Enhance apoptotic sensitivity
- Akt activators: Inhibit caspase-9 phosphorylation
Caspase-9 activation can be measured:
- Activity assays: Fluorometric substrates
- Cleavage products: Western blot for p37/p10 fragments
- Caspase-9 activity in CSF: Potential biomarker for neurodegeneration
The study of Caspase 9 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.
- Protein information and structure. UniProt Database.
- Li P, et al. (1997) Cytochrome c and dATP-dependent formation of Apaf-1/caspase-9 complex initiates an apoptotic protease cascade. Cell 91:479-489. PMID:9390557
- Thornberry NA, Lazebnik Y (1998) Caspases: Guardians of the death sentence. Cell 94:745-750. PMID:9753317
- Green DR, Kroemer G (2005) The cell biology of apoptosis. Nature Reviews Molecular Cell Biology 6:265-275. PMID:15719087
- Riedl SJ, Shi Y (2004) Molecular mechanisms of caspase regulation during apoptosis. Nature Reviews Molecular Cell Biology 5:897-907. PMID:15520809
- Holcik M, Korneluk RG (2001) XIAP, the guardian of the apoptotic pathway. Nature Reviews Molecular Cell Biology 2:550-556. PMID:11433371
- Datta SR, et al. (2000) Akt phosphorylation of caspase-9 and suppression of apoptosis. Cell 103:1043-1056. PMID:11136050
- Yuan J, Yankner BA (2000) Apoptosis in the nervous system. Nature 407:802-809. PMID:11048724
[1] Protein information and structure. UniProt Database.
[1] Protein information. UniProt Database.