| TCHH | |||||||||||||||||||||||||||||||||||||||||||||||||||
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| Identifiers | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Aliases | TCHH , THH, THL, TRHY, trichohyalin, UHS3 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| External IDs | OMIM: 190370; MGI: 2177944; GeneCards: TCHH; OMA:TCHH - orthologs | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Trichohyalin is a protein that in mammals is encoded by the TCHH gene. [5]
| TCHH | |||||||||||||||||||||||||||||||||||||||||||||||||||
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| Identifiers | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Aliases | TCHH , THH, THL, TRHY, trichohyalin, UHS3 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| External IDs | OMIM: 190370; MGI: 2177944; GeneCards: TCHH; OMA:TCHH - orthologs | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Trichohyalin is a protein that in mammals is encoded by the TCHH gene. [5]
In 1903 the name trichohyalin was assigned to the granules of the inner root sheath (IRS) of hair follicles discovered by Hans Vörner. [6] In 1986 the name was reassigned to a protein isolated from sheep wool follicles. [7]
The human TCHH is located on the long (q) arm of chromosome 1 at region 2 band 1 sub-band 3 (1q21.3), from base pair 152,105,403 to base pair 152,116,368 (map). [8] This region in chromosome 1q21 is known as the epidermal differentiation complex, since it harbors over fifty other genes involved in keratinocyte differentiation.
Gene coding sequence contains 5829 nucleotides. [9] Gene orthologs were identified in most mammals including mice, chickens, rats, pigs, sheep, horses and other species. [10]
Trichohyalin is highly expressed in the inner root sheath cells of the hair follicle and medulla. [11] It was also detected in the granular layer and stratum corneum of normal epidermis, [12] newborn human foreskin epidermis, the hard palate, in the nail matrix, the filiform papillae of dorsal tongue epithelium and in rodent forestomach. [13]
The protein forms frequent links between the heads and tails of the keratin chains and, thus, participates in keratin intermediate filaments (KIF) inter-filamentous cross-linking. It also carries a function of a major reinforcement cross-bridging protein for the cell envelope (CE) barrier structure of the IRS and participates in coordination of CE structure. [11]
Overall, trichohyalin confers mechanical strength to the hair follicle inner root sheath and to other toughened epithelial tissues. [11]
Trichohyalin belongs to the S100-fused protein family. It is a monomer, containing 1943 amino acids, [14] and has elongated (>200 nm) single-stranded alpha-helical conformation based on its unusually high content of charged residues. [15]
Molecular mass of the human trichohyalin is 253925 Da. [14]
The protein includes nine domains. Domain 1 contains two EF-hand calcium-binding domains. Domains 2-4, 6, and 8 are almost entirely alpha-helical, configured as a series of peptide repeats of varying regularity, and are thought to form a single-stranded alpha-helical rod stabilised by ionic interactions. Domain 6 is the most regular and may bind KIF directly by ionic interactions. Domains 5 and 7 are less well organised and may induce folds in the molecule. Domain 9 contains the C-terminus, conserved among different species. [14] [15]
TCHH protein is extensively cross-linked to itself in the IRS tissue as well as to keratin intermediate filaments (KIF). All TCHH-keratin links involved only domain 6 or 8 sequences. [11]
The protein can also form cross-links to all other CE proteins including involucrin, envoplakin, keratin, repetin, desmoplakin, SPR1, SPR2, and LEP. [11]
TCHH-TCHH and TCHH-CE protein links are distributed among domains 2–5, but are uncommon in domains 6 and 8. Most intra-THH cross-links occurred in the least organised domain 5 region at a 3.5-fold higher frequency. [11]
Trichohyalin is associated with uncombable hair syndrome, [17] human alopecia areata [18] and also may be linked to curly hair phenotype in Europeans. [19]
A weak expression of the protein was discovered in the horny layer of psoriasis, ichthyosis, keratosis pilaris, porokeratosis, chronic dermatitis and callus. [20] The same level of trichohyalin expression was found in epidermal tumours (seborrheic keratosis, actinic keratosis, Bowen's disease, well-differentiated squamous cell carcinoma) and follicular tumours (trichoepithelioma, keratotic basal cell epithelioma, proliferating trichilemmal tumour, trichilemmoma, pilomatricoma and keratoacanthoma). [20]
Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer of the skin are sometimes referred to as basal keratinocytes. Keratinocytes form a barrier against environmental damage by heat, UV radiation, water loss, pathogenic bacteria, fungi, parasites, and viruses. A number of structural proteins, enzymes, lipids, and antimicrobial peptides contribute to maintain the important barrier function of the skin. Keratinocytes differentiate from epidermal stem cells in the lower part of the epidermis and migrate towards the surface, finally becoming corneocytes and eventually being shed, which happens every 40 to 56 days in humans.
Keratin 1 is a Type II intermediate filament (IFs) of the intracytoplasmatic cytoskeleton. Is co-expressed with and binds to Keratin 10, a Type I keratin, to form a coiled coil heterotypic keratin chain. Keratin 1 and Keratin 10 are specifically expressed in the spinous and granular layers of the epidermis. In contrast, basal layer keratinocytes express little to no Keratin 1. Mutations in KRT1, the gene encoding Keratin 1, have been associated with variants of the disease bullous congenital ichthyosiform erythroderma in which the palms and soles of the feet are affected. Mutations in KRT10 have also been associated with bullous congenital ichthyosiform erythroderma; however, in patients with KRT10 mutations the palms and soles are spared. This difference is likely due to Keratin 9, rather than Keratin 10, being the major binding partner of Keratin 1 in acral keratinocytes.
Type II keratins constitutes the Type II intermediate filaments (IFs) of the intracytoplasmatic cytoskeleton, which is present in all mammalian epithelial cells. The type 2 cytokeratins consist of basic or neutral, high molecular weight proteins which in vivo are arranged in pairs of heterotypic Type I and Type II keratin chains, coexpressed during differentiation of simple and stratified epithelial tissues. It has been seen that Type II Keratins are developed before Type 1 keratins during human embryonic development.
Hair keratin is a type of keratin found in hair and the nails.
Desmoplakin is a protein in humans that is encoded by the DSP gene. Desmoplakin is a critical component of desmosome structures in cardiac muscle and epidermal cells, which function to maintain the structural integrity at adjacent cell contacts. In cardiac muscle, desmoplakin is localized to intercalated discs which mechanically couple cardiac cells to function in a coordinated syncytial structure. Mutations in desmoplakin have been shown to play a role in dilated cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy, where it may present with acute myocardial injury; striate palmoplantar keratoderma, Carvajal syndrome and paraneoplastic pemphigus.
Nestin is a protein that in humans is encoded by the NES gene.
Protein-glutamine gamma-glutamyltransferase K is a transglutaminase enzyme that in humans is encoded by the TGM1 gene.
Corneocytes are terminally differentiated keratinocytes and compose most of the stratum corneum, the outermost layer of the epidermis. They are regularly replaced through desquamation and renewal from lower epidermal layers and are essential for its function as a skin barrier.
Keratohyalin is a protein structure found in cytoplasmic granules of the keratinocytes in the stratum granulosum of the epidermis. Keratohyalin granules (KHG) mainly consist of keratin, profilaggrin, loricrin and trichohyalin proteins which contribute to cornification or keratinization, the process of the formation of epidermal cornified cell envelope. During the keratinocyte differentiation, these granules maturate and expand in size, which leads to the conversion of keratin tonofilaments into a homogenous keratin matrix, an important step in cornification.
Involucrin is a protein component of human skin and in humans is encoded by the IVL gene. In binding the protein loricrin, involucrin contributes to the formation of a cell envelope that protects corneocytes in the skin.
Small proline-rich protein 3 is a protein that in humans is encoded by the SPRR3 gene, which is found within the epidermal differentiation complex (EDC).
Loricrin is a protein that in humans is encoded by the LOR gene.
Epiplakin is a protein that in humans is encoded by the EPPK1 gene. It belongs to the family of plakin proteins and is found in the human epidermis. It consists of 13 domains which are all similar to the B domain located at the C terminus of the human epidermal and cardiac muscle protein desmoplakin. The domains in epiplakin range from 46 to 70% in their homology to this B domain in desmoplakin. It was first identified as an autoantigen in a person who suffers from a rare autoimmune skin disease. Epiplakin was sequenced to have a total of 5065 amino acid residues and based on its amino acid composition it has a molecular weight of about 552 kDa. The EPPK1 gene is notable for a lack of introns over its coding region - its entire 15 kbp coding region is encoded by a single exon.
Envoplakin is a protein that in humans is encoded by the EVPL gene.
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.
The KRT86 gene encodes for keratin, type II cuticular Hb6 protein in humans.
Cornifin-A is a protein that in humans is encoded by the SPRR1A gene.
Keratin, type II cytoskeletal 78 is a protein that in humans is encoded by the KRT78 gene.
The epidermal differentiation complex (EDC) is a gene complex comprising over fifty genes encoding proteins involved in the terminal differentiation and cornification of keratinocytes, the primary cell type of the epidermis. In humans, the complex is located on a 1.9 Mbp stretch within chromosome 1q21. The proteins encoded by EDC genes are closely related in terms of function, and evolutionarily they belong to three distinct gene families: the cornified envelope precursor family, the S100 protein family and the S100 fused type protein (SFTP) family.
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