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Keratin is one of a family of fibrous structural proteins known as scleroproteins. α-Keratin is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, calluses, and the outer layer of skin among vertebrates. Keratin also protects epithelial cells from damage or stress. Keratin is extremely insoluble in water and organic solvents. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals. The only other biological matter known to approximate the toughness of keratinized tissue is chitin. Keratin comes in two types, the primitive, softer forms found in all vertebrates and harder, derived forms found only among sauropsids . Keratin resists digestion, which is why cats regurgitate hairballs.
The integumentary system comprises the skin and its appendages acting to protect the body from various kinds of damage, such as loss of water or damages from outside. The integumentary system includes hair, scales, feathers, hooves, and nails. It has a variety of additional functions; it may serve to waterproof, and protect the deeper tissues, excrete wastes, and regulate body temperature, and is the attachment site for sensory receptors to detect pain, sensation, pressure, and temperature.
A nail is a claw-like keratinous plate at the tip of the fingers and toes in most primates. Nails correspond to claws found in other animals. Fingernails and toenails are made of a tough protective protein called alpha-keratin which is a polymer and found in the hooves, hair, claws and horns of vertebrates.
Intermediate filaments (IFs) are cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate Branchiostoma.
Keratin 6A is one of the 27 different type II keratins expressed in humans. Keratin 6A was the first type II keratin sequence determined. Analysis of the sequence of this keratin together with that of the first type I keratin led to the discovery of the four helical domains in the central rod of keratins. In humans Keratin 6A is encoded by the KRT6A gene.
Cytokeratins are keratin proteins found in the intracytoplasmic cytoskeleton of epithelial tissue. They are an important component of intermediate filaments, which help cells resist mechanical stress. Expression of these cytokeratins within epithelial cells is largely specific to particular organs or tissues. Thus they are used clinically to identify the cell of origin of various human tumors.
Keratin 6C, is a type II cytokeratin, one of a number of isoforms of keratin 6 encoded by separate genes located within the type II keratin gene cluster on human chromosome 12q. This gene was uncovered recently by the Human Genome Project and its expression patterns in humans remains unknown.
Keratin, type II cuticular Hb1 is a protein that in humans is encoded by the KRT81 gene.
Keratin, type I cuticular Ha1 is a protein that in humans is encoded by the KRT31 gene.
Keratin, type II cuticular Hb6 is a protein that in humans is encoded by the KRT86 gene.
Keratin, type II cytoskeletal 78 is a protein that in humans is encoded by the KRT78 gene.
Keratin, type I cuticular Ha3-II is a protein that in humans is encoded by the KRT33B gene.
Keratin, type I cuticular Ha2 is a protein that in humans is encoded by the KRT32 gene.
Keratin, type I cuticular Ha3-I is a protein that in humans is encoded by the KRT33A gene.
Keratin, type I cuticular Ha4 is a protein that in humans is encoded by the KRT34 gene.
Keratin, type II cuticular Hb5 is a protein that in humans is encoded by the KRT85 gene.
Keratin, type I cuticular Ha6 is a protein that in humans is encoded by the KRT36 gene.
Keratin 83, also known as KRT83, is a protein which humans is encoded by the KRT83 gene.
Keratin 37 is a protein that in humans is encoded by the KRT37 gene. KRT37 is a member of the keratin gene family.
Alpha-keratin, or α-keratin, is a type of keratin found in vertebrates. This protein is the primary component in hairs, horns, mammalian claws, nails and the epidermis layer of the skin. α-keratin is a fibrous structural protein, meaning it is made up of amino acids that form a repeating secondary structure. The secondary structure of α-keratin is very similar to that of a traditional protein α-helix and forms a coiled coil. Due to its tightly wound structure, it can function as one of the strongest biological materials and has various functions in mammals, from predatory claws to hair for warmth. α-keratin is synthesized through protein biosynthesis, utilizing transcription and translation, but as the cell matures and is full of α-keratin, it dies, creating a strong non-vascular unit of keratinized tissue.
References
- ↑ Langbein L, Schweizer J (2005). Keratins of the human hair follicle. Int Rev Cytol. International Review of Cytology. 243. pp. 1–78. doi:10.1016/S0074-7696(05)43001-6. ISBN 9780123646477. PMID 15797458.
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