A class of proteins common in skin, hair, and wool.
Is one of a family of fibrous structural proteins.
It is the key structural material making up hair, horns, claws, hooves, and the outer layer of human skin.
It is a protein that protects epithelial cells from damage or stress.
It is extremely insoluble in water and organic solvents.
Keratin filaments are abundant in keratinocytes in the cornified layer of the epidermis.
Keratin filaments are proteins which have undergone keratinization.
Keratin filaments are present in epithelial cells in general.
The acidic keratins are found on chromosome 17 (17q21.2).
The human genome encodes 54 functional keratin genes which are located in two clusters on chromosomes 12 and 17.
There are two distinct but homologous keratin families, Type I keratin and Type II keratins.
Fibrous keratin molecules supercoil to form stable filaments consisting of multiple copies of the keratin monomer.
Hydrophobic interactions along the keratins helical segments keep the coiled structure.
Keratins have large amounts of the sulfur-containing amino acid cysteine, required for the disulfide bridges.
Disulfide bridges confer additional strength and rigidity by permanent, thermally stable crosslinking.
Human hair is approximately 14% cysteine.
The smells of burning hair and skin are due to the volatile sulfur compounds formed.
Extensive disulfide bonding contributes to the insolubility of keratins.
Keratin filaments are intermediate filaments.
Cornification refers to the development of an epidermal barrier in stratified squamous epithelial tissue.
Cornification is characterised by:
production of keratin
production of small proline-rich proteins and transglutaminase which form a cornified cell envelope beneath the plasma membrane
Cellular metabolism ceases.
With epithelial differentiation, cells become cornified as keratin protein is incorporated into longer keratin intermediate filaments.
Eventually the epithelial cell’s nucleus and cytoplasmic organelles disappear, metabolism ceases and cells undergo a programmed death as they become fully keratinized.
Keratin filaments and other intermediate filaments function as part of the cytoskeleton to mechanically stabilize the cell against physical stress through connections to desmosomes, cell-cell junctional plaques, and hemidesmosomes, cell-basement membrane adhesive structures.
Cells in the epidermis contain a structural matrix of keratin, which makes this outermost layer of the skin almost waterproof.
Collagen and elastin in the epidermis gives skin its strength.
Rubbing and pressure cause thickening of the outer, cornified layer of the epidermis and form protective calluses.
Calluses are hard, integumentary structures formed by intercellular cementing of fibers formed from the dead, cornified cells generated by specialized beds deep within the skin.
Some infectious fungi, such as those that cause athlete’s foot and ringworm feed on keratin.
Diseases caused by mutations in the keratin genes include:
Epidermolysis bullosa simplex
Ichthyosis bullosa of Siemens
Rhabdoid cell formation in Large cell lung carcinoma with rhabdoid phenotype.
Tumors that express keratin include: carcinomas, thymomas, sarcomas and trophoblastic neoplasms.
The expression pattern of keratin subtypes allows prediction of the origin of the primary tumor: hepatocellular carcinomas typically express K8 and K18, and cholangiocarcinomas express K7, K8 and K18, while metastases of colorectal carcinomas express K20, but not K7.
Keratin is highly resistant to digestive acids if it is ingested, and cats who regularly ingest hair eventually result in the formation of a hairball.
It has a high proportion of cysteine amino acids with high-strength disulphide bonds giving keratin the dual properties of both strength and flexibility.