keratines

Keratines, also known as keratin proteins, are a family of fibrous structural proteins that form the intermediate filament cytoskeleton of epithelial cells. They are encoded by dozens of keratin genes and are grouped into type I (acidic) and type II (basic to neutral) keratins, which pair to form heterodimers and assemble into larger filaments. Keratines are expressed in a tissue-specific manner, most prominently in skin, hair, nails, feathers, beaks, and other integumentary structures.

Two major forms are recognized: soft keratins, which constitute the keratin filaments in most simple epithelia and the epidermal layer, and hard keratins found in hair, nails, horns, and beaks. Hard keratins are unusually rich in cysteine, producing extensive disulfide cross-links that confer rigidity and resistance to mechanical and chemical challenges. β-keratins are found in reptile and bird epidermis and differ structurally from mammalian α-keratins.

Keratines are synthesized in differentiating keratinocytes and assembled into cytoskeletal networks that support cell shape, mechanical integrity, and barrier function. Mutations in keratin genes can destabilize the keratin network, leading to skin fragility disorders such as epidermolysis bullosa simplex and various keratinopathies.

Outside the body, keratines and their hydrolysates are used in cosmetics and dermatology to improve hair strength and porosity. Keratin-derived materials are also explored for wound healing, tissue engineering, and biomaterials, though therapeutic benefits depend on the source, processing, and application context.