Keratin 6A
Encyclopedia
Keratin 6A is a protein
that in humans is encoded by the KRT6A gene
.
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).
, 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 follicle
s. 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.
, 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.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that in humans is encoded by the KRT6A gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
Keratins
Keratins are the intermediate filamentIntermediate filament
Intermediate filaments are a family of related proteins that share common structural and sequence features. Intermediate filaments have an average diameter of 10 nanometers, which is between that of 7 nm actin , and that of 25 nm microtubules, although they were initially designated...
proteins that form a dense meshwork of filaments throughout the cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within 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
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
-specific and cellular differentiation
Cellular differentiation
In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...
-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
Hair
Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....
and nail
Nail (anatomy)
A nail is a horn-like envelope covering the dorsal aspect of the terminal phalanges of fingers and toes in humans, most non-human primates, and a few other mammals. Nails are similar to claws, which are found on numerous other animals....
are known as "hard keratins" or "trichocyte
Trichocyte
In mammals, trichocytes are the specialized epithelial cells from which the highly mechanically resilient tissues hair and nails are formed. They can be identified by the fact that they express "hard", "trichocyte" or "hair" keratin proteins...
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
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
-containing amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
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
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
17q, whereas the genes for type II keratins are located in a cluster on human chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
12q (the exception being K18, a type I keratin located in the type II gene cluster).
Keratin 6A
Keratin 6A (protein name K6A; gene name KRT6A), is a type II cytokeratinKeratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
, one of a number of isoforms of keratin 6 encoded by separate genes located within the type II keratin gene cluster on human chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
12q. It is found with keratin 16
Keratin 16
Keratin 16 is a protein that in humans is encoded by the KRT16 gene.Keratin 16 is a type I cytokeratin. It is paired with keratin 6 in a number of epithelial tissues, including nail bed, esophagus, tongue, and hair follicles...
and/or keratin 17
Keratin 17
Keratin, type I cytoskeletal 17 is a protein that in humans is encoded by the KRT17 gene.Keratin 17 is a type I cytokeratin. It is found in nail beds, hair follicles, sebaceous glands, and other epidermal appendages...
in the palm and sole epidermis, the epithelial cells of the nail bed, the filiform papillae of the tongue
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
, the epithelial lining of oral mucosa and esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
, as well as the hair follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
s. 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
Keratin 6B
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...
and keratin 6C
Keratin 6C
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...
are encoded by the neighbouring genes, which are identical in intron
Intron
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...
-exon
Exon
An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...
organization to KRT6A and are more than 99% identical in their DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
coding sequences.
Genetic disorders
Mutations in the genes expressing this protein have been associated with the PC1 variant of pachyonychia congenitaPachyonychia congenita
Pachyonychia congenita, also called Jadassohn-Lewandowski Syndrome or simply pachyonychia, is an autosomal dominant skin disorder.-Symptoms:Common symptoms include:*Excess keratin in nail beds and thickening of the nails...
, 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.