Keratiinia

Keratiinia, commonly referred to as keratin, is a family of fibrous structural proteins that form the intermediate filament cytoskeleton of epithelial cells. Keratins are highly resilient and largely insoluble, with a high cysteine content that allows disulfide cross-links, contributing to their mechanical strength. They are a major component of hair, nails, claws, horns, and the outer layer of the skin.

There are two broad groups of keratins: alpha-keratins and beta-keratins. Alpha-keratins predominate in mammals and assemble into the keratin filaments found in hair, nails, and the epidermis. Beta-keratins are found in reptiles and birds and contribute to the strength of scales, beaks, and feathers. Keratins are encoded by a large family of genes (the KRT gene family) and are co-expressed with keratin-associated proteins to form robust filament networks.

Biosynthesis occurs in keratinocytes as they differentiate in the epidermis. The filaments provide structural support and help form the protective barrier of the skin. During keratinization, keratinocytes shrink and become corneocytes, which accumulate keratin and eventually form the stratum corneum, the skin’s outermost protective layer.

Clinically, mutations in keratin genes can cause skin fragility and other disorders, such as epidermolysis bullosa simplex and pachyonychia congenita. Keratins also have applications in cosmetics and biomaterials, with keratin-rich extracts used in hair care products and as components in medical and industrial materials.

The term derives from Greek kerat-, meaning horn, reflecting its early association with horn-like tissues.