Keratin ( ) is one of the fibrous structural protein families. It is the main structural material that forms the hair, horns, claws, nails, and outer layers of human skin. Keratin is also a protein that protects epithelial cells from damage or stress. Keratin is very insoluble in water and organic solvents. Keratin monomers converge into bundles to form a hard, intermediate filament and form a non-mineralized epidermal appendix found in reptiles, birds, amphibians, and mammals. The only other known biological problem close to the toughness of keratin tissue is chitin.
Video Keratin
Etymology
Keratin comes from the Greek ???????? keratÃÆ'ni from ????? hard (genitive ??????? keratos ) that means "horns" derived from Proto-Indo-Europe * ? er â € <â € < - of the same meaning. It consists of "horns like", that is, kerato , in which chemical suffix -in is added. Greek hard is used in many animal names, e.g. Rhinoceros , which means "nose with horn".
Maps Keratin
Examples of events
Keratin filaments overflow in keratinocytes in the cornified epidermal layer; this is a protein that has undergone keratinization. In addition, keratin filaments present in epithelial cells in general. For example, mouse thymic epithelial cells (TECs) are known to react with antibodies to keratin 5, keratin 8, and keratin 14. These antibodies are used as fluorescent markers to distinguish the TEC subsets in the genetic studies of the thymus.
- - keratin found in all vertebrates. They form hair (including wool), stratum corneum, horns, nails, claws and mammal nails and hagfish mucus.
- harder ? - keratin is found only in sauropsid, it's all reptiles and live birds. They are found in nails, scales, and reptile claws, some reptile shells (Testudines, like turtles, turtles, terrapins), and in feathers, beaks, and birds' claws. (Keratin is mainly formed in beta sheets, but beta sheets are also found in? -keratins.)
In addition, the baleen slab of the filter eater is made of keratin.
Keratin (also described as cytokeratins) is a type I and type II intermediate filament polymer, found only in the chordata genome (vertebrates, Amphioxus, urochordata). Nematodes and many other non-akordate animals appear to have only medium-type VI filaments, lamins, which have a long-stem domain (vs. short-stem domain for keratin).
Gen
The human genome encodes 54 functional keratin genes located in two groups on chromosomes 12 and 17. This suggests that they are derived from a series of gene duplications on this chromosome.
Keratin includes the following proteins which are KRT23, KRT24, KRT25, KRT26, KRT27, KRT28, KRT31, KRT32, KRT33A, KRT33B, KRT34, KRT35, KRT36, KRT37, KRT38, KRT39, KRT40, KRT71, KRT72, KRT73, KRT74, KRT75 , KRT76, KRT77, KRT78, KRT79, KRT8, KRT80, KRT81, KRT82, KRT83, KRT84, KRT85 and KRT86 have been used to describe keratin above 20.
Structure of protein
The first sequence of keratin is determined by Hanukoglu and Fuchs. This sequence reveals that there are two different keratin families but the homologues are referred to as Type I keratin and Type II keratin. By analyzing the primary structures of keratin and other intermediate filament proteins, Hanukoglu and Fuchs suggested models that medium-keratin and protein filaments contain a residue domain of ~ 310 with four inner segments? - aid lessons separated by three short connecting segments are predicted to be in beta-turn conformation. This model has been confirmed by the determination of the crystal structure of the keratin helical domain.
The supercoil fibrous keratin molecules form a highly stable left-hand superhellical motif for multimerise, forming filaments consisting of copies of many keratin monomers.
The main force that makes the coil-coil structure is the hydrophobic interaction between apolar residues along the keratin helical segment.
Limited interior space is the reason why the triple helix of collagen structural proteins (unrelated), found on the skin, cartilage and bone, also has a high percentage of glycine. Elastin connective tissue proteins also have a high percentage of both glycine and alanine. Fibroin silk, regarded as? - keratin, can have two of these as 75-80% of the total, with 10-15% serine, with the rest having large side groups. An antiparallel chain, with alternate C -> N orientation. A dominant amino acid with small non-reactive groups is characteristic for structural proteins, where binding close to H-bond is more important than chemical specificity.
Disulfide bridges
In addition to intra- and intermolecular hydrogen bonds, a feature that distinguishes keratin is the presence of a large number of sulfur-containing amino acid cysteine, which is required for disulphide bridges which provide additional strength and stiffness with permanent and thermally stable crosslinks - in the same way as non sulfur bridges -protein that stabilizes vulcanised rubber. Human hair is about 14% cysteine. The stinging smell of burning hair and skin is due to the volatile sulfur compounds formed. Large disulfide bonds contribute to keratin infertility, except in small amounts of solvents such as separating or reducing agents.
More flexible and elastic hair keratin has fewer interchain disulfide bridges than keratin in mammal nails, nails and claws (homologous structures), which are harder and more like their analogs in other vertebrate classes. Hair and others? -keratins consist of? -helly circular single strand protein (with intra-regular chain H-link), which then is further twisted into a superhellical rope that can be rolled further. The -keratin of the reptiles and birds have sheets twisted together, then stabilized and hardened by disulphide bridges.
Filament formation
It theorizes that keratin is combined to be 'hard' and 'soft', or 'cytokeratin' and 'other keratin'. The model is now understood correctly. The new nuclear addition in 2006 to illustrate keratin considers this.
Keratin filaments are intermediate filaments. Like all medium filaments, keratin proteins form a filamentous polymer in a series of assembly steps starting with dimerization; The dimer assembles into tetramer and octamers and finally, if the current hypothesis holds, the unit-length-filament (ULF) can be an end-to-end anneal into a long filament.
Pair
Cornification
Cornification is the process of forming epidermal barrier in epithelial tissue of squamous epithelium. At the cellular level, the certificate is marked by:
- keratin production
- the production of small proline-rich (SPRR) proteins and transglutaminases that eventually form the cornified envelope cells beneath the plasma membrane
- terminal differentiation
- loss of core and organel, in final stage of certi fi cation
Metabolism stops, and the cells are almost completely filled by keratin. During the epithelial differentiation process, cells become cornified as keratin proteins inserted into longer keratin medium filaments. Eventually the core organ and cytoplasm disappears, metabolism stops and cells undergo programmed death when they become completely keratinized. In many other types of cells, such as dermis cells, keratin filaments and other intermediate filaments serve as part of the cytoskeleton to mechanically stabilize cells against physical stress. It does this through connections to the desmosomes, junctional plaque cells, and hemidesmosomes, the cell-basement membrane adhesive structure.
The cells in the epidermis contain a structural matrix of keratin, which makes the outermost layer of the skin almost impermeable, and along with collagen and elastin, gives its skin strength. Rubbing and pressure causes the thickening of the outer layer, the cornified epidermis and forming a protective callus, which is useful for athletes and at the fingertips of musicians who play stringed instruments. The keratinized epidermal cells are constantly released and replaced.
These hard and enclosed structures are formed by interselular cementing of fibers formed from dead and cornified cells produced by special beds deep within the skin. Hair grows continuously and feathers moult and regenerate. The constituent proteins may be phylogenetically homologous but somewhat different in the chemical and organizational structures of the supermodecule. The evolutionary relationship is complicated and only partially known. Several genes have been identified for "keratin-in feathers, and these may be characteristic of all keratin.
Silk
Silk fibroins produced by insects and spiders are often classified as keratin, although it is not clear whether they are phylogenetically linked to vertebrate keratin.
The silk found on insect cocoons, and in spider webs and egg sheaths, also has twisted sheets into fibers that are incorporated into larger supermolecular aggregates. The spinneret structure of the spider's tail, and the contribution of their interior glands, provides exceptional rapid extrusion control. Spider silk is usually about 1 to 2 micrometers (Ã,Âμm) thick, compared to about 60 Âμm for human hair, and more for some mammals. The biological and commercial properties of biological and commercial silk fibers depend on the organization of several adjacent protein chains to hard-crystal regions of varying sizes, alternating with flexible and amorphous regions where the chain is randomly bound. A somewhat analogous situation occurs with synthetic polymers such as nylon, developed as a substitute for silk. Silk from a hornet cocoon contains a doblet about 10 Âμm, with a core and a layer, and can be arranged up to 10 layers, also in variable form. Adult bees also use silk as a glue, just like spiders.
Clinical interests
Some fungi are contagious, such as the fungus that causes athlete's foot and ringworm (ie dermatophytes), or Batrachochytrium dendrobatidis (Chytrid fungus), eating keratin.
Diseases caused by mutations in the keratin gene include:
- Epidermolysis bullosa simplex
- Ichthyosis bullosa from Siemens
- Epidermolytic hyperkeratosis
- Steatocystoma multiplex
- Pharyngis keratosis
- The formation of Rhabdoid cells in large cell lung carcinoma with rhabdoid phenotype
The expression of keratin is helpful in determining the origin of the epithelium in anaplastic cancers. Tumors expressing keratin include carcinoma, thymoma, sarcoma and trophoblastic neoplasms. Furthermore, the exact expression pattern of the keratin subtype allows prediction of the origin of the primary tumor when assessing metastasis. For example, hepatocellular carcinoma usually expresses K8 and K18, and cholangiocarcinoma expresses K7, K8 and K18, whereas colorectal colorectal metastases express K20, but not K7.
Keratin is very resistant to digestive acid if digested (Trichophagia). Therefore, cats (who take care of themselves with their tongues) regularly digest hair that will ultimately result in the formation of hair balls that sometimes vomit when it becomes too large. Rapunzel syndrome is a very rare but potentially fatal human condition in humans caused by Tricophagia.
See also
- List of skin conditions caused by mutations in keratin
- The keratin list is expressed in a masking human system
- List of keratins
References
External links
- The composition and structure of the silk-sheet
- Hair-Science.com entry on hair microscopic elements
- Proteopedia page in keratins
Source of the article : Wikipedia
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