Editing Type II keratin

'''Type II keratins''' (or '''Type II cytokeratins''') 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 [[protein]]s 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.<ref name=":0">{{cite journal |last1=Schweizer |first1=Jürgen |last2=Bowden |first2=Paul E. |last3=Coulombe |first3=Pierre A. |last4=Langbein |first4=Lutz |last5=Lane |first5=E. Birgitte |last6=Magin |first6=Thomas M. |last7=Maltais |first7=Lois |last8=Omary |first8=M. Bishr |last9=Parry |first9=David A.D. |last10=Rogers |first10=Michael A. |last11=Wright |first11=Mathew W. |title=New consensus nomenclature for mammalian keratins |url=https://rupress.org/jcb/article/174/2/169/44323/New-consensus-nomenclature-for-mammalian-keratins |journal=[[Journal of Cell Biology]] |volume=174 |number=2 |access-date=1 June 2023 |archive-url=https://web.archive.org/web/20200211221441/https://rupress.org/jcb/article/174/2/169/44323/New-consensus-nomenclature-for-mammalian-keratins |archive-date=2020-02-11 |pages=169{{ndash}}174 |language=en |doi=10.1083/jcb.200603161 |date=17 July 2006 |pmid=16831889 |url-status=live|pmc=2064177 }}</ref> It has been seen that Type II Keratins are developed before Type 1 keratins during human embryonic development.<ref>{{Cite journal |last1=Lu |first1=Hong |last2=Hesse |first2=Michael |last3=Peters |first3=Bettina |last4=Magin |first4=Thomas M. |date=August 2005 |title=Type II keratins precede type I keratins during early embryonic development |url=https://pubmed.ncbi.nlm.nih.gov/16180309/ |journal=European Journal of Cell Biology |volume=84 |issue=8 |pages=709–718 |doi=10.1016/j.ejcb.2005.04.001 |issn=0171-9335 |pmid=16180309}}</ref>

Type II cytokeratins are encoded on [[chromosome 12]]q and encompasses: [[Keratin 1|CK1]], [[Keratin 2|CK2]], [[Keratin 3|CK3]], [[CK4]], [[CK5]], [[CK6]], [[CK7]] and [[CK8]]. Their molecular weight ranges from 52 kDa (CK8) to 67 kDa (CK18).

Overall, keratin type 2 plays a crucial role in maintaining the strength and integrity of the skin, hair, and nails. Mutations in [[keratin]] genes can lead to various genetic disorders that affect these tissues, such as [[epidermolysis bullosa simplex]], a rare condition characterized by blistering and erosion of the skin and mucous membranes.<ref name=":1">{{Cite journal |last1=Moll |first1=Roland |last2=Divo |first2=Markus |last3=Langbein |first3=Lutz |date=2008-06-01 |title=The human keratins: biology and pathology |url=https://doi.org/10.1007/s00418-008-0435-6 |journal=Histochemistry and Cell Biology |language=en |volume=129 |issue=6 |pages=705–733 |doi=10.1007/s00418-008-0435-6 |issn=1432-119X |pmc=2386534 |pmid=18461349}}</ref>

== Keratin 2 Types: 2A and 2B ==
Type II Keratins are divided into 2 subtypes: Type IIA Keratins and Type IIB Keratins. Type 2A keratins are expressed in tissues that require high levels of mechanical stress, such as the soles of the feet, while type 2B keratins are expressed in tissues that are subject to less stress, such as the palms of the hands.<ref name=":0" />

=== Type IIA Keratins ===
[[File:KRT1 Structure with type 2 highlighted.png|thumb|From Uniprot.  Figure shows the structure of KRT1 gene. The helix is formed by the type II keratins in green, and the type I keratins in grey.  The green coils consists of type IIA and IIB keratins. Expressed in upper leg skin, mammalian vulva, upper arm skin and 106 other tissues.<ref>{{cite web |title=KRT1 expression in human |url=https://bgee.org/gene/ENSG00000167768 |website=www.bgee.org |access-date=1 June 2023 |language=en }}</ref> Located on Chromosome 12, localized in the cell membrane and cytoplasm.<ref>{{Cite web |title=UniProt |url=https://www.uniprot.org/uniprotkb/P04264/entry#subcellular_location |access-date=2023-05-03 |website=www.uniprot.org}}</ref>]]
Type IIA Keratins are characterized by their expression in tissues that undergo high stress, like soles of the feet or palms of the hand. There are several different type 2A keratins that have been identified in humans, including [[KRT1|K1]], [[KRT2|K2]], [[Keratin 9|K9]], [[Keratin 10|K10]], [[KRT77|K77]], and [[KRT78|K78]]. These keratins are expressed in a tissue-specific manner, with K1, K2, and K10 being predominantly expressed in the epidermis, while K9, K77, and K78 are expressed in the nail bed and hair follicles.<ref name=":1" />

Type IIA keratins have a unique structural feature that allows them to form coiled-coil dimers, which then assemble into tetramers and eventually into intermediate filaments. This structural organization provides the mechanical strength and resilience necessary to withstand the stresses experienced by the tissues in which they are expressed.<ref>{{Cite journal |last1=Irvine |first1=A. D. |last2=McLean |first2=W. H. |date=May 1999 |title=Human keratin diseases: the increasing spectrum of disease and subtlety of the phenotype-genotype correlation |journal=The British Journal of Dermatology |volume=140 |issue=5 |pages=815–828 |doi=10.1046/j.1365-2133.1999.02810.x |issn=0007-0963 |pmid=10354017|s2cid=21429676 |doi-access=free }}</ref> Mutations in type 2A keratin genes can lead to various genetic disorders, such as [[epidermolytic hyperkeratosis]] (EHK) and [[palmoplantar keratoderma]] (PPK), which are characterized by [[hyperkeratosis]] and blistering of the skin on the palms and soles.<ref>{{Cite journal |last1=Chamcheu |first1=Jean Christopher |last2=Siddiqui |first2=Imtiaz A. |last3=Syed |first3=Deeba N. |last4=Adhami |first4=Vaqar M. |last5=Liovic |first5=Mirjana |last6=Mukhtar |first6=Hasan |date=2011-04-15 |title=Keratin Gene Mutations in Disorders of Human Skin and its Appendages |journal=Archives of Biochemistry and Biophysics |volume=508 |issue=2 |pages=123–137 |doi=10.1016/j.abb.2010.12.019 |issn=0003-9861 |pmc=3142884 |pmid=21176769}}</ref>

=== Type IIB Keratins ===
Type IIB keratins are a group of intermediate filament proteins that are primarily expressed in epithelial tissues, such as the skin, nails, and hair follicles. They belong to the keratin family of proteins, which are characterized by their highly conserved alpha-helical coiled-coil domains.<ref name=":2">{{Cite journal |last=Justin T. Jacob, Pierre A. Coulombe, Raymond Kwan, and M. Bishr Omary |title=Types I and II Keratin Intermediate Filaments |journal=Cold Spring Harbor Perspectives in Biology |date=2018 |volume=10 |issue=4 |pages=a018275 |doi=10.1101/cshperspect.a018275 |pmid=29610398 |pmc=5880164 }}</ref> Keratin type IIB is encoded by the [[KRT6B]] gene and is often co-expressed with the equivalent keratin type IIA (KRT6A) in a variety of epithelial tissues.<ref>{{cite journal |last1=Hatzfeld |first1=M. |last2=Burba |first2=M. |title=Function of type I and type II keratin head domains: their role in dimer, tetramer and filament formation |url=https://journals.biologists.com/jcs/article/107/7/1959/24207/Function-of-type-I-and-type-II-keratin-head |journal=[[Journal of Cell Science]] |access-date=1 June 2023 |archive-url=https://web.archive.org/web/20220804165456/https://journals.biologists.com/jcs/article/107/7/1959/24207/Function-of-type-I-and-type-II-keratin-head |archive-date=2022-08-04 |pages=1959{{ndash}}1972 |language=en |doi=10.1242/jcs.107.7.1959 |date=1 July 1994 |url-status=live |volume=107 |number=7|url-access=subscription }}</ref> Together, these two proteins form [[heterodimers]] that assemble into intermediate filaments, which provide mechanical stability and resistance to mechanical stress.<ref name=":2" /> In addition to their structural role, type IIB keratins have been shown to play important roles in wound healing, inflammation, and cell migration. Dysregulation of type IIB keratin expression or mutations in the KRT6B gene have been associated with a variety of skin disorders, including psoriasis, epidermolysis bullosa, and pachyonychia congenita.<ref name=":2" />

==See also==
*[[Type I keratin]]

==References==
{{Reflist}}

==External links==
* {{MeshName|Type+II+Keratin}}
* [http://www.proteopedia.org/wiki/index.php/Keratins Proteopedia page on keratins]

{{Cytoskeletal Proteins}}
{{Fibrous proteins}}

[[Category:Keratins]]