A list of keratins is a systematic compilation of the keratin family of structural proteins that are expressed in epithelial cells of vertebrates. Keratins belong to the intermediate filament protein superfamily and are categorized primarily into two types based on their biochemical properties, genomic organization, and cellular localization:
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Type I keratins (acidic) – encoded by the KRT (formerly KRT1–KRT18) gene cluster on human chromosome 17 and other loci. Representative members include KRT9, KRT10, KRT12, KRT14, KRT16, KRT17, KRT18, KRT19, KRT20, KRT23, KRT24, KRT31–KRT40, and many others. These proteins generally heterodimerize with type II keratins to form intermediate filaments.
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Type II keratins (basic‑to‑neutral) – encoded by the KRT (formerly KRT1–KRT8) gene cluster on human chromosome 12 and other chromosomes. Representative members include KRT1, KRT2, KRT5, KRT6A, KRT6B, KRT6C, KRT7, KRT8, KRT13, KRT14, KRT15, KRT17, KRT18, KRT71, KRT73, KRT75, KRT77, and related paralogs.
In addition to the canonical epithelial keratins, there are hair‑type keratins (often designated with the “KRT” prefix followed by a number in the 30s–40s) that form the rigid filaments in hair, nails, feathers, and related structures. These include KRT31–KRT40 in humans, which are expressed predominantly in the inner root sheath and cuticle of hair follicles.
The compilation typically includes the following information for each keratin entry:
| Symbol | Gene | Type | Tissue/Cell Specificity | Known Isoforms | Clinical Relevance |
|---|---|---|---|---|---|
| KRT1 | KRT1 | II | Suprabasal epidermis | K1A, K1B | Epidermolytic ichthyosis |
| KRT5 | KRT5 | II | Basal layer of epidermis | K5A | Epidermolysis bullosa simplex |
| KRT14 | KRT14 | I | Basal layer of epidermis | K14A, K14B | Epidermolysis bullosa simplex |
| KRT17 | KRT17 | I | Nail beds, hair follicles | K17A | Pachyonychia congenita |
| … | … | … | … | … | … |
Historical development
The keratin nomenclature was standardized by the International Committee on Standardized Nomenclature for Human Genes (HUGO) and the Human Genome Organisation (HUGO) Gene Nomenclature Committee (HGNC). Early studies in the 1970s identified keratin proteins by electrophoretic mobility (e.g., K1–K20). Subsequent molecular cloning and sequencing refined the classification into the current type I/II system.
Functional overview
Keratin proteins polymerize into heterodimers (type I with type II) that assemble into 10 nm intermediate filaments, providing mechanical resilience to epithelial cells. They also participate in intracellular signaling, cell adhesion, and stress responses. Mutations in specific keratin genes are linked to a spectrum of dermatological disorders, including epidermolysis bullosa simplex, epidermolytic hyperkeratosis, and various forms of ichthyosis and pachyonychia congenita.
Representative species coverage
While most curated lists focus on human (Homo sapiens) keratins, comparative entries for model organisms such as Mus musculus (mouse), Rattus norvegicus (rat), Gallus gallus (chicken), and Danio rerio (zebrafish) are often included, reflecting evolutionary conservation and divergence within the keratin superfamily.
References and sources
Comprehensive lists are derived from peer‑reviewed literature, genomic databases (e.g., NCBI Gene, Ensembl, UniProt), and specialized resources such as the Keratin Gene Database. These sources provide accession numbers, sequence data, expression profiles, and documented disease associations.
See also
- Intermediate filament proteins
- Cytoskeletal architecture
- Epidermolysis bullosa simplex
- Hair biology
External links
- HGNC Gene Symbol Report: Keratin family (https://www.genenames.org)
- UniProtKB entry for human keratin proteins (https://www.uniprot.org)
Note: The above table presents illustrative examples; a complete list contains over 50 distinct keratin genes across type I and type II categories.
