Keratin 6A is one of the 27 different type II keratins expressed in humans. Keratin 6A was the first type II keratin sequence determined. [3] 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. [3] In humans Keratin 6A is encoded by the KRT6A gene. [4] [5]
Keratins are the intermediate filament proteins that form a dense meshwork of filaments throughout the cytoplasm of epithelial cells. Keratins form heteropolymers consisting of a type I and a type II keratin. Keratins are generally expressed in particular pairs of type I and type II keratin proteins in a tissue-specific and cellular differentiation-specific manner.
The keratin proteins of epithelial tissues are commonly known as "keratins" or are sometimes referred to as "epithelial keratins" or "cytokeratins". The specialized keratins of hair and nail are known as "hard keratins" or "trichocyte keratins". Trichocytes are the specialized epithelial cells from which hair and nail are composed. Trichocyte keratins are similar in their gene and protein structure to keratins except that they are especially rich in the sulfur-containing amino acid cysteine, which facilitates chemical cross-linking of the assembled hard keratins to form a more structurally resilient material.
Both epithelial keratins and hard keratins can be further subdivided into type I (acidic) keratins and type II (neutral-basic) keratins. The genes for the type I keratins are located in a gene cluster on human chromosome 17q, whereas the genes for type II keratins are located in a cluster on human chromosome 12q (the exception being K18, a type I keratin located in the type II gene cluster).
Keratin 6A (protein name K6A; gene name KRT6A), 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. It is found with keratin 16 and/or keratin 17 in the palm and sole epidermis, the epithelial cells of the nail bed, the filiform papillae of the tongue, the epithelial lining of oral mucosa and esophagus, as well as the hair follicles. This keratin 6 isoform is thought to be the most abundant of the K6 isoforms.
The KRT6A gene consists of 9 exons separated by 8 introns and is located in the type II keratin gene cluster on human chromosome 12q. Keratin 6B and keratin 6C are encoded by the neighbouring genes, which are identical in intron-exon organization to KRT6A and are more than 99% identical in their DNA coding sequences.
Keratin 6A has been shown to have antimicrobial properties, and is the main antimicrobial factor in the eye. [6]
Mutations in the genes expressing this protein is associated with the PC-K6A subtype of pachyonychia congenita, an inherited disorder of the epithelial tissues in which keratin 6A is expressed, particularly leading to structural abnormalities of the nails, the epidermis of the palms and soles, and oral epithelia. [7] [8] [9]
The expression of keratin 6A is often tested together with keratin 5, using CK5/6 antibodies, which target both keratin forms. [10]
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. Excessive keratinization participate in fortification of certain tissues such as in horns of cattle and rhinos, and armadillos' osteoderm. 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.
Keratin, type II cytoskeletal 7 also known as cytokeratin-7 (CK-7) or keratin-7 (K7) or sarcolectin (SCL) is a protein that in humans is encoded by the KRT7 gene. Keratin 7 is a type II keratin. It is specifically expressed in the simple epithelia lining the cavities of the internal organs and in the gland ducts and blood vessels.
Keratin, type I cytoskeletal 4 also known as cytokeratin-4 (CK-4) or keratin-4 (K4) is a protein that in humans is encoded by the KRT4 gene.
Keratin 3 also known as cytokeratin 3 is a protein that in humans is encoded by the KRT3 gene. Keratin 3 is a type II cytokeratin. It is specifically found in the corneal epithelium together with keratin 12.
Keratin 14 is a member of the type I keratin family of intermediate filament proteins. Keratin 14 was the first type I keratin sequence determined. Keratin 14 is also known as cytokeratin-14 (CK-14) or keratin-14 (KRT14). In humans it is encoded by the KRT14 gene.
Keratin 13 is a protein that in humans is encoded by the KRT13 gene.
Keratin, type I cytoskeletal 10 also known as cytokeratin-10 (CK-10) or keratin-10 (K10) is a protein that in humans is encoded by the KRT10 gene. Keratin 10 is a type I keratin.
Keratin, type I cytoskeletal 19 also known as cytokeratin-19 (CK-19) or keratin-19 (K19) is a 40 kDa protein that in humans is encoded by the KRT19 gene. Keratin 19 is a type I keratin.
Keratin 18 is a type I cytokeratin. It is, together with its filament partner keratin 8, perhaps the most commonly found products of the intermediate filament gene family. They are expressed in single layer epithelial tissues of the body. Mutations in this gene have been linked to cryptogenic cirrhosis. Two transcript variants encoding the same protein have been found for this gene.
Keratin, type I cytoskeletal 17 is a protein that in humans is encoded by the KRT17 gene.
Keratin 16 is a protein that in humans is encoded by the KRT16 gene.
Keratin 5, also known as KRT5, K5, or CK5, is a protein that is encoded in humans by the KRT5 gene. It dimerizes with keratin 14 and forms the intermediate filaments (IF) that make up the cytoskeleton of basal epithelial cells. This protein is involved in several diseases including epidermolysis bullosa simplex and breast and lung cancers.
Keratin 6B is a type II cytokeratin, one of a number of isoforms of keratin 6. It is found with keratin 16 and/or keratin 17 in the hair follicles, the filiform papillae of the tongue and the epithelial lining of oral mucosa and esophagus. This keratin 6 isoform is thought be less abundant than the closely related keratin 6A protein. Mutations in the gene encoding this protein have been associated with pachyonychia congenita, an inherited disorder of the epithelial tissues in which this keratin is expressed, particularly leading to structural abnormalities of the nails, the epidermis of the palms and soles, and oral epithelia. Keratin 6B is associated with the PC-K6B subtype of pachyonychia congenita.
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 Hb6 is a protein that in humans is encoded by the KRT86 gene.
Keratin, type I cuticular Ha3-II is a protein that in humans is encoded by the KRT33B gene.
Keratin, type I cytoskeletal 23 is a protein that in humans is encoded by the KRT23 gene.
Keratin, type I cuticular Ha3-I is a protein that in humans is encoded by the KRT33A gene.
Keratin, type II cuticular Hb5 is a protein that in humans is encoded by the KRT85 gene.
Keratin 83, also known as KRT83, is a protein which humans is encoded by the KRT83 gene.
