KLK1 (Kallikrein 1) is a member of the kallikrein family of serine proteases, primarily known for its roles in the kinin system, blood pressure regulation, and inflammation. While predominantly studied in peripheral tissues, emerging evidence indicates KLK1 is expressed in the brain and may play complex roles in neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD).
| KLK1 Protein |
|---|
| Protein Name | Kallikrein 1 (KLK1) |
| Gene | [KLK1](/genes/klk1) |
| UniProt ID | [P06858](https://www.uniprot.org/uniprot/P06858) |
| Molecular Weight | ~29 kDa (mature), ~39 kDa (proenzyme) |
| Subcellular Localization | Secreted (extracellular) |
| Protein Family | Kallikrein (Serine protease) family |
| Expression | Kidney, pancreas, brain, salivary glands |
KLK1 is a secreted serine protease with classical protease architecture:
- Signal peptide: N-terminal secretion signal
- Propeptide: Maintains latency until activation cleavage
- Catalytic domain: Serine protease fold with His-Asp-Ser catalytic triad
- Kallikrein domain: Specific substrate binding region
The active enzyme cleaves at specific arginine and lysine residues in target proteins.
- Bradykinin generation: Cleaves low and high molecular weight kininogens to release bradykinin
- Vasodilation: Bradykinin causes blood vessel relaxation
- Blood pressure: Contributes to blood pressure regulation
- Pain and inflammation: Mediates inflammatory responses
- Tissue remodeling: Proteolytic activity in extracellular matrix
- Coagulation: Interactions with clotting cascade
- Cell proliferation: Growth factor-like effects
- Brain expression: KLK1 is expressed in neurons and glia
- Amyloid processing: May interact with APP and Aβ metabolism
- Neuroinflammation: Kinin system contributes to chronic inflammation
- Blood-brain barrier: May affect BBB integrity
- Therapeutic targeting: KLK1 inhibitors are being explored
- Dopaminergic neurons: Expression in substantia nigra
- Oxidative stress: Kinins may modulate oxidative responses
- Neuroinflammation: Pro-inflammatory effects in PD
- Motor dysfunction: Kinin receptor involvement in motor control
¶ Stroke and Vascular Dementia
- Blood-brain barrier: KLK1 contributes to BBB disruption
- Cerebral edema: Kinin-mediated vascular permeability
- Hemorrhagic injury: Implications for stroke outcomes
- B1 receptor antagonists: Target inducible kinin receptors
- B2 receptor antagonists: Block constitutive bradykinin effects
- Inhibitors: Small molecule and peptide inhibitors
- Gene therapy: RNA-based approaches
The kinin system signals through two main receptors:
- B1 receptor (BDKRB1): Inducible, upregulated during inflammation
- B2 receptor (BDKRB2): Constitutively expressed, mediates most bradykinin effects
Chronic neuroinflammation in AD and PD involves the kinin system:
- Pro-inflammatory: Kinins potentiate cytokine release
- Blood-brain barrier: Increase BBB permeability
- Edema formation: Contribute to vasogenic edema
Kinin receptor antagonists represent potential therapeutics:
- B1 antagonists: Icatibant, BI113823
- B2 antagonists: Lebrikizumab experimental compounds
- KLK1 inhibitors: Reduce bradykinin generation