Betakeratins

Beta-keratins, also known as corneous beta-proteins, are a family of structural proteins found in the epidermis of sauropsids, which include reptiles and birds. They form hard, often highly cross-linked tissues such as feathers, scales, beaks, and claws. In contrast to the alpha-keratins of mammals, beta-keratins assemble into beta-sheet–rich structures that can be packed into rigid, insoluble matrices.

Molecularly, beta-keratins are characterized by a relatively high cysteine content, which promotes extensive disulfide cross-links. This cross-linking contributes to their stiffness, reduced elasticity, and resistance to water and mechanical wear. Their deposition occurs during keratinization, producing durable, protective layers in the integument.

The beta-keratin gene family is expanded and organized in clusters within sauropsid genomes. Diversification of these genes is associated with the evolution of feathers and other keratinized structures, enabling a range of forms from flight-related plumage to protective scales. Beta-keratins are generally absent from mammals, which rely predominantly on alpha-keratins for their epidermal tissues.

Biologically, beta-keratin–based tissues provide mechanical strength, waterproofing, and abrasion resistance. Feathers derive largely from beta-keratins, while reptilian scales and avian beaks and claws rely on these proteins for rigidity and protective function. The unique properties of beta-keratins have also made them a subject of interest in evolutionary biology and biomaterials research, as scientists explore how beta-sheet–rich keratin networks contribute to durable, lightweight structures.