Keratin

Keratin is a family of fibrous structural proteins that forms the intermediate filament framework of epithelial cells and constitutes a major component of hair, nails, horns, claws, hooves, and the outer keratinized layer of the skin. There are two main keratin types: alpha-keratins, which assemble into soft keratin in vertebrate skin and hair, and beta-keratins, found in reptiles and birds and forming harder keratin in scales, beaks, claws, and feathers.

Keratin proteins are encoded by large multigene families (KRTs) and are often co-expressed with keratin-associated proteins that assist cross-linking. They assemble as coiled-coil dimers that form 10-nanometer intermediate filaments, providing mechanical strength and resilience to tissues. The abundance of cysteine residues in keratins enables disulfide bonding, which increases rigidity and resistance to degradation.

Mutations in keratin genes can disrupt filament networks and lead skin and nail disorders, including epidermolysis bullosa simplex (KRT5, KRT14) and pachyonychia congenita (KRT6A, KRT16, KRT17). Such conditions are typically inherited in an autosomal dominant pattern and exhibit epidermal fragility and nail abnormalities.

In humans, keratins are widely studied for cosmetics and biomedical applications. Industrially, keratin-rich materials are obtained from hair or wool and processed for use in biomaterials, wound dressings, and hair-care products. Keratin's biocompatibility and structural properties drive ongoing research into keratin-based films, fibers, and composites.