| Gene |
PCDH15 |
| UniProt |
Q9P1E5 |
| PDB |
AlphaFold predicted |
| Mol. Weight |
210 kDa |
| Localization |
Hair cell stereocilia tips |
| Family |
Cadherin superfamily, protocadherin subfamily |
| Diseases |
Usher Syndrome Type 1, Non-syndromic Deafness |
Protocadherin 15 (PCDH15) is a ~210 kDa member of the cadherin superfamily that forms the lower tip link in hair cell stereocilia of the inner ear. The tip link connects the stereocilia's mechanotransduction channel to the gating machinery, converting mechanical deflection into electrical signals.
PCDH15 is essential for hearing and balance. Mutations cause Usher syndrome type 1 (USH1) and non-syndromic deafness. The protein undergoes alternative splicing to produce multiple isoforms with distinct expression patterns.
¶ Domain Architecture
PCDH15 has a complex multi-domain structure:
- ** signal peptide**: N-terminal signal sequence for secretion
- Extracellular domain: Contains 11 cadherin repeats with calcium-binding motifs
- EC1-11 repeats (~650 aa each)
- Conserved motif at each repeat boundary
- EC1 interacts with CDH23 to form the tip link
- Transmembrane domain: Single-pass membrane anchor
- Cytoplasmic domain: Contains PDZ-binding motif for protein interactions
- Binds to Myosin VIIa via PDZ domain proteins
- Links to the ankle link complex
PCDH15 forms the lower portion of the tip link:
- Tip link formation: PCDH15-CDH23 heterodimer forms the tip link
- Mechanical gating: Transmits deflection force to the mechanotransduction channel
- Channel regulation: Controls the open probability of the channel
- Tip link regeneration: Required for recovery after noise-induced tip link damage
PCDH15 interacts with:
- Myosin VIIa: Motor protein that transports PCDH15 to stereocilia tips
- Ankle link proteins: Form the ankle link complex at the stereocilia base
- Whirlin: Scaffold protein that localizes to stereocilia tips
During development:
- Initial stereocilia formation requires PCDH15
- Establishment of planar cell polarity
- Maturation of the mechanotransduction machinery
PCDH15 mutations cause USH1, characterized by:
- Profound congenital deafness
- Retinitis pigmentosa (starting in childhood)
- Severe vestibular dysfunction (balance problems from birth)
Over 150 pathogenic variants identified:
- Missense mutations: Often cause milder disease
- Truncating mutations: Cause severe USH1
- Variants affecting tip link formation are most severe
Some PCDH15 mutations cause isolated hearing loss:
- Autosomal recessive inheritance
- Prelingual onset
- Typically profound
- Loss of tip link function → no mechanotransduction
- Failure of hair bundle development
- Disruption of the ankle link complex
- AAV-mediated PCDH15 delivery in development
- Achieved hearing restoration in mouse models
- Challenges: large gene size, delivery to inner ear
- Pharmacological stabilization: Enhance protein function
- Antisense oligonucleotides: Exon skipping for splice-site mutations
- Protein folding correctors: For misfolded mutants
Effective for USH1 patients:
- Bypasses hair cell dysfunction
- Highly successful with early implantation
For retinitis pigmentosa:
- Neurotrophic factors
- Gene therapy for PCDH15 (in development)
- Stem cell approaches
When Protocadherin-15 is referenced in disease pages:
- Evidence level: Strong for USH1 (causative gene)
- Mechanistic plausibility: High — direct role in mechanotransduction
- Therapeutic relevance: Emerging — gene therapy in clinical trials