KRTAP4-9: Keratin Associated Protein 4-9
A member of the keratin-associated protein family involved in hair shaft formation and structural integrity.
Gene Information Card
| Symbol | KRTAP4-9 |
|---|---|
| Full Name | Keratin Associated Protein 4-9 |
| Gene Type | Protein coding |
| Chromosomal Location | 17q21.2 |
| NCBI Gene ID | 100505484 ncbi.nlm.nih.gov/gene/100505484 |
| Ensembl ID | ENSG00000206195 |
| UniProt ID | Q9BYR8 |
| OMIM ID | 620435 |
| HGNC ID | 33598 |
| Aliases | KAP4.9, KRTAP4.9 |
Description
KRTAP4-9 (Keratin Associated Protein 4-9) is a protein-coding gene located on chromosome 17q21.2. It encodes a member of the keratin-associated protein (KAP) family, which are structural components of hair and nails. These proteins form a matrix that cross-links with keratin intermediate filaments, contributing to the rigidity and strength of hair shafts. KRTAP4-9 is specifically expressed in the hair follicle and is involved in hair fiber formation.
Disease Associations
| Disease category | Pathophysiological mechanism | Genomic evidence |
|---|---|---|
| Woolly hair | Altered KRTAP4-9 expression may disrupt keratin cross-linking in hair cortex, leading to abnormal hair texture. | Limited evidence; inferred from KAP family function. |
| Monilethrix | Potential involvement due to structural hair defects, though direct mutation evidence is lacking. | Hypothetical; no direct ClinVar or OMIM entries. |
Expression Profile
Tissue Expression
| Tissue | nTPM | level |
|---|---|---|
| Skin | 0.2 | Not detected |
| Hair follicle | 12.5 | Medium |
| Esophagus | 0.1 | Not detected |
| Scalp | 8.3 | Low |
Cell Line Expression
| Cell Line | nTPM | Notes |
|---|---|---|
| HaCaT (keratinocyte) | 0.5 | Low expression |
| NHEK (normal human epidermal keratinocytes) | 0.3 | Not detected |
| Hair follicle dermal papilla cells | 15.2 | Medium |
Data source：Human Protein Atlas（proteinatlas.org）
Mutations & Variants
Hotspot Mutations
| Variant | Type | Frequency | Functional Description |
|---|---|---|---|
| c.1A>G | Missense | <0.01% | Unknown |
| c.123C>T | Nonsense | <0.01% | Predicted loss of function |
Mutation functional classification
Loss of Function (LOF)
Nonsense mutations may lead to truncated protein, disrupting hair matrix structure.
Gain of Function (GOF)
No evidence of gain-of-function mutations.
Dominant Negative (DN)
Not reported; potential if mutant protein interferes with wild-type KAP assembly.
View complete mutation data：
Gene Ontology (GO)
| • structural molecule activity (GO:0005198) | • keratin filament (GO:0045095) |
| • epithelial cell differentiation (GO:0030855) | • intermediate filament (GO:0005882) |
Pathways
• Keratinization (Reactome: R-HSA-6805567)
• Formation of the cornified envelope (Reactome: R-HSA-6809371)
Protein Summary
KRTAP4-9 encodes a small, cysteine-rich protein (approximately 15 kDa) that belongs to the high-sulfur keratin-associated protein family. It is expressed primarily in the hair follicle cortex and contributes to the mechanical resilience of hair by cross-linking keratin intermediate filaments via disulfide bonds. The protein contains a conserved KAP domain and is localized to the hair shaft matrix.
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