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Keratin

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(Redirected fromCornification)
Structural fibrous protein
Not to be confused withCarotene orCreatine.
Microscopy of keratin filaments inside cells

Keratin (/ˈkɛrətɪn/[1][2]) is one of a family of structuralfibrous proteins also known asscleroproteins. It is the key structural material making upscales,hair,nails,feathers,horns,claws,hooves, and the outer layer ofskin in vertebrates. Keratin also protectsepithelial cells from damage or stress. Keratin is extremely insoluble in water and organic solvents. Keratinmonomers assemble into bundles to formintermediate filaments, which are tough and form strongunmineralized epidermal appendages found inreptiles,birds,amphibians, andmammals.[3][4] Excessive keratinization participate in fortification of certain tissues such as in horns ofcattle andrhinos, andarmadillos'osteoderm.[5] The only otherbiological matter known to approximate thetoughness of keratinized tissue ischitin.[6][7][8]Keratin comes in two types: the primitive, softer forms found in all vertebrates and the harder, derived forms found only amongsauropsids (reptiles and birds).

Spider silk is classified as keratin,[9] although production of the protein may have evolved independently of the process in vertebrates.

Examples of occurrence

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Thehorns of theimpala are made of keratin covering a core ofbone.

Alpha-keratins (α-keratins) are found in all vertebrates. They form thehair (includingwool), theouter layer of skin,horns,nails,claws andhooves of mammals, and the slime threads ofhagfish.[4] Thebaleen plates of filter-feedingwhales are also made of keratin.Keratin filaments are abundant inkeratinocytes in the hornified layer of theepidermis; these are proteins which have undergonekeratinization. They are also present in epithelial cells in general. For example, mouse thymic epithelial cells react withantibodies for keratin 5, keratin 8, and keratin 14. These antibodies are used asfluorescent markers to distinguish subsets of mousethymic epithelial cells in genetic studies of thethymus.

The harderbeta-keratins (β-keratins) are found only in thesauropsids, i.e., all livingreptiles andbirds. They are found in the nails,scales, and claws ofreptiles, in some reptileshells (Testudines), and in thefeathers,beaks, and claws ofbirds.[10] These keratins are formed primarily inbeta sheets. However, beta sheets are also found in α-keratins.[11]Recent scholarship has shown that sauropsid β-keratins are fundamentally different from α-keratins at a genetic and structural level. The new termcorneous beta protein (CBP) has been proposed to avoid confusion with α-keratins.[12]

Keratins (also described ascytokeratins) arepolymers of type I and type IIintermediate filaments that have been found only inchordates (vertebrates,amphioxi,urochordates).Nematodes and many other non-chordate animals seem to have only type VIintermediate filaments,fibers that structure the nucleus.

Genes

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This section mayrequirecleanup to meet Wikipedia'squality standards. The specific problem is:Not particularly helpful to dump a big list of KRT genes here. Using the source a bit more to explain what each gene and each zone of genes mean will be helpful, as we currently have no particular examples of a hair keratin. Please helpimprove this section if you can.(October 2022) (Learn how and when to remove this message)
The neutral–basic keratins are encoded on chromosome 12 (12q13.13).
The acidic keratins are encoded on chromosome 17 (17q21.2).

Thehuman genome encodes 54 functional keratingenes, located in two clusters onchromosomes 12 and 17. This suggests that they originated from a series of gene duplications on these chromosomes.[13]

The keratins include the following proteins of whichKRT23,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 andKRT86 have been used to describe keratins past 20.[14]

Table of keratin genes and biological processes (GeneCards)[15]
SymbolBiological process
KRT1complement activation, lectin pathway
KRT1retina homeostasis
KRT1response to oxidative stress
KRT1peptide cross-linking
KRT1keratinization
KRT1fibrinolysis
KRT1intermediate filament organization
KRT1regulation of angiogenesis
KRT1negative regulation of inflammatory response
KRT1protein heterotetramerization
KRT1establishment of skin barrier
KRT10morphogenesis of an epithelium
KRT10epidermis development
KRT10peptide cross-linking
KRT10keratinocyte differentiation
KRT10epithelial cell differentiation
KRT10positive regulation of epidermis development
KRT10protein heterotetramerization
KRT12morphogenesis of an epithelium
KRT12visual perception
KRT12epidermis development
KRT12epithelial cell differentiation
KRT12cornea development in camera-type eye
KRT13cytoskeleton organization
KRT13epithelial cell differentiation
KRT13regulation of translation in response to stress
KRT13intermediate filament organization
KRT14aging
KRT14epidermis development
KRT14keratinocyte differentiation
KRT14epithelial cell differentiation
KRT14hair cycle
KRT14intermediate filament organization
KRT14intermediate filament bundle assembly
KRT14stem cell differentiation
KRT15epidermis development
KRT15epithelial cell differentiation
KRT15intermediate filament organization
KRT16morphogenesis of an epithelium
KRT16inflammatory response
KRT16cytoskeleton organization
KRT16aging
KRT16keratinocyte differentiation
KRT16negative regulation of cell migration
KRT16epithelial cell differentiation
KRT16keratinization
KRT16hair cycle
KRT16innate immune response
KRT16intermediate filament cytoskeleton organization
KRT16intermediate filament organization
KRT16keratinocyte migration
KRT16establishment of skin barrier
KRT17morphogenesis of an epithelium
KRT17positive regulation of cell growth
KRT17epithelial cell differentiation
KRT17hair follicle morphogenesis
KRT17keratinization
KRT17intermediate filament organization
KRT17positive regulation of translation
KRT17positive regulation of hair follicle development
KRT18cell cycle
KRT18anatomical structure morphogenesis
KRT18tumor necrosis factor-mediated signaling pathway
KRT18obsolete Golgi to plasma membrane CFTR protein transport
KRT18Golgi to plasma membrane protein transport
KRT18negative regulation of apoptotic process
KRT18intermediate filament cytoskeleton organization
KRT18extrinsic apoptotic signaling pathway
KRT18hepatocyte apoptotic process
KRT18cell-cell adhesion
KRT19Notch signaling pathway
KRT19epithelial cell differentiation
KRT19response to estrogen
KRT19intermediate filament organization
KRT19sarcomere organization
KRT19cell differentiation involved in embryonic placenta development
KRT2keratinocyte development
KRT2epidermis development
KRT2peptide cross-linking
KRT2keratinization
KRT2keratinocyte activation
KRT2keratinocyte proliferation
KRT2intermediate filament organization
KRT2positive regulation of epidermis development
KRT2keratinocyte migration
KRT20apoptotic process
KRT20cellular response to starvation
KRT20epithelial cell differentiation
KRT20intermediate filament organization
KRT20regulation of protein secretion
KRT23epithelial cell differentiation
KRT23intermediate filament organization
KRT24biological_process
KRT25cytoskeleton organization
KRT25aging
KRT25hair follicle morphogenesis
KRT25hair cycle
KRT25intermediate filament organization
KRT26
KRT27biological_process
KRT27hair follicle morphogenesis
KRT27intermediate filament organization
KRT28biological_process
KRT3epithelial cell differentiation
KRT3keratinization
KRT3intermediate filament cytoskeleton organization
KRT3intermediate filament organization
KRT31epidermis development
KRT31epithelial cell differentiation
KRT31intermediate filament organization
KRT32epidermis development
KRT32epithelial cell differentiation
KRT32intermediate filament organization
KRT33Aepithelial cell differentiation
KRT33Aintermediate filament organization
KRT33Baging
KRT33Bepithelial cell differentiation
KRT33Bhair cycle
KRT33Bintermediate filament organization
KRT34epidermis development
KRT34epithelial cell differentiation
KRT34intermediate filament organization
KRT35anatomical structure morphogenesis
KRT35epithelial cell differentiation
KRT35intermediate filament organization
KRT36biological_process
KRT36epithelial cell differentiation
KRT36intermediate filament organization
KRT36regulation of keratinocyte differentiation
KRT37epithelial cell differentiation
KRT37intermediate filament organization
KRT38epithelial cell differentiation
KRT38intermediate filament organization
KRT39epithelial cell differentiation
KRT39intermediate filament organization
KRT4cytoskeleton organization
KRT4epithelial cell differentiation
KRT4keratinization
KRT4intermediate filament organization
KRT4negative regulation of epithelial cell proliferation
KRT40epithelial cell differentiation
KRT40intermediate filament organization
KRT5epidermis development
KRT5response to mechanical stimulus
KRT5regulation of cell migration
KRT5keratinization
KRT5regulation of protein localization
KRT5intermediate filament polymerization
KRT5intermediate filament organization
KRT6Aobsolete negative regulation of cytolysis by symbiont of host cells
KRT6Amorphogenesis of an epithelium
KRT6Apositive regulation of cell population proliferation
KRT6Acell differentiation
KRT6Akeratinization
KRT6Awound healing
KRT6Aintermediate filament organization
KRT6Adefense response to Gram-positive bacterium
KRT6Acytolysis by host of symbiont cells
KRT6Aantimicrobial humoral immune response mediated by antimicrobial peptide
KRT6Anegative regulation of entry of bacterium into host cell
KRT6Bectoderm development
KRT6Bkeratinization
KRT6Bintermediate filament organization
KRT6Ckeratinization
KRT6Cintermediate filament cytoskeleton organization
KRT6Cintermediate filament organization
KRT7keratinization
KRT7intermediate filament organization
KRT71hair follicle morphogenesis
KRT71keratinization
KRT71intermediate filament organization
KRT72biological_process
KRT72keratinization
KRT72intermediate filament organization
KRT73biological_process
KRT73keratinization
KRT73intermediate filament organization
KRT74keratinization
KRT74intermediate filament cytoskeleton organization
KRT74intermediate filament organization
KRT75hematopoietic progenitor cell differentiation
KRT75keratinization
KRT75intermediate filament organization
KRT76cytoskeleton organization
KRT76epidermis development
KRT76keratinization
KRT76pigmentation
KRT76intermediate filament organization
KRT76sebaceous gland development
KRT77biological_process
KRT77keratinization
KRT77intermediate filament organization
KRT78keratinization
KRT78intermediate filament organization
KRT79keratinization
KRT79intermediate filament organization
KRT8keratinization
KRT8tumor necrosis factor-mediated signaling pathway
KRT8intermediate filament organization
KRT8sarcomere organization
KRT8response to hydrostatic pressure
KRT8response to other organism
KRT8cell differentiation involved in embryonic placenta development
KRT8extrinsic apoptotic signaling pathway
KRT8hepatocyte apoptotic process
KRT80keratinization
KRT80intermediate filament organization
KRT81keratinization
KRT81intermediate filament organization
KRT82biological_process
KRT82keratinization
KRT82intermediate filament organization
KRT83aging
KRT83epidermis development
KRT83keratinization
KRT83hair cycle
KRT83intermediate filament organization
KRT84hair follicle development
KRT84keratinization
KRT84nail development
KRT84intermediate filament organization
KRT84regulation of keratinocyte differentiation
KRT85epidermis development
KRT85keratinization
KRT85intermediate filament organization
KRT86keratinization
KRT86intermediate filament organization
KRT9spermatogenesis
KRT9epidermis development
KRT9epithelial cell differentiation
KRT9skin development
KRT9intermediate filament organization
Protein sequence alignment of human keratin 1, 2A, 3,4, 5, 6A, 7, and 8 (KRT1 – KRT8). Only the first rod domain is shown above. Alignment was created usingClustal Omega.

Protein structure

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The first sequences of keratins were determined byIsrael Hanukoglu andElaine Fuchs (1982, 1983).[16][17] These sequences revealed that there are two distinct but homologous keratin families, which were named type I and type II keratins.[17] By analysis of the primary structures of these keratins and other intermediate filament proteins, Hanukoglu and Fuchs suggested a model in which keratins and intermediate filament proteins contain a central ~310 residue domain with four segments in α-helical conformation that are separated by three short linker segments predicted to be in beta-turn conformation.[17] This model has been confirmed by the determination of the crystal structure of a helical domain of keratins.[18]

Type I and II keratins

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The human genome has 54 functional annotated keratin genes, of which 28 aretype I keratins and 26 aretype II keratins.[19]

Keratin (high molecular weight) inbile duct cell and oval cells ofhorseliver.

Fibrous keratin molecules supercoil to form a very stable, left-handedsuperhelical motif to multimerise, forming filaments consisting of multiple copies of the keratinmonomer.[20]

The major force that keeps the coiled-coil structure ishydrophobic interactions betweenapolar residues along the keratin's helical segments.[21]

Limited interior space is the reason why thetriple helix of the (unrelated) structural proteincollagen, found inskin,cartilage andbone, likewise has a high percentage ofglycine. The connective tissue proteinelastin also has a high percentage of both glycine andalanine.Silkfibroin, considered a β-keratin, can have these two as 75–80% of the total, with 10–15%serine, with the rest having bulky side groups. The chains are antiparallel, with an alternating C → N orientation.[22] A preponderance ofamino acids with small,nonreactive side groups is characteristic of structural proteins, for which H-bonded close packing is more important thanchemical specificity.

Disulfide bridges

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In addition to intra- and intermolecularhydrogen bonds, the distinguishing feature of keratins is the presence of large amounts of thesulfur-containing amino acidcysteine, required for thedisulfide bridges that confer additional strength and rigidity by permanent, thermally stablecrosslinking[23]—in much the same way that non-protein sulfur bridges stabilizevulcanizedrubber. Human hair is approximately 14% cysteine. Thepungent smells of burning hair and skin are due to the volatile sulfur compounds formed. Extensive disulfide bonding contributes to theinsolubility of keratins, except in a small number of solvents such asdissociating orreducing agents.

A humantoenail that fell off after a small trauma.

The more flexible and elastic keratins of hair have fewer interchain disulfide bridges than the keratins inmammalianfingernails, hooves and claws (homologous structures), which are harder and more like their analogs in other vertebrate classes.[24] Hair and other α-keratins consist ofα-helically coiled single protein strands (with regular intra-chainH-bonding), which are then further twisted into superhelicalropes that may be further coiled. The β-keratins of reptiles and birds have β-pleated sheets twisted together, then stabilized and hardened by disulfide bridges.

Thiolated polymers (thiomers) can form disulfide bridges with cysteine substructures of keratins getting covalently attached to these proteins.[25] Thiomers therefore exhibit high binding properties to keratins found in hair,[26] on skin[27][28] and on the surface of many cell types.[29]

Filament formation

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It has been proposed that keratins can be divided into 'hard' and 'soft' forms, or 'cytokeratins' and 'other keratins'.[clarification needed][dubious –discuss] That model is now understood to be correct. A new nuclear addition in 2006 to describe keratins takes this into account.[14]

Keratin filaments areintermediate filaments. Like all intermediate filaments, keratin proteins form filamentous polymers in a series of assembly steps beginning with dimerization; dimers assemble into tetramers and octamers and eventually, if the current hypothesis holds, into unit-length-filaments (ULF) capable ofannealing end-to-end into long filaments.

Pairing

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A (neutral-basic)B (acidic)Occurrence
keratin 1,keratin 2keratin 9,keratin 10stratum corneum,keratinocytes
keratin 3keratin 12cornea
keratin 4keratin 13stratified epithelium
keratin 5keratin 14,keratin 15stratified epithelium
keratin 6keratin 16,keratin 17squamous epithelium
keratin 7keratin 19ductal epithelia
keratin 8keratin 18,keratin 20simple epithelium

Cornification

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Cornification is the process of forming an epidermal barrier instratified squamous epithelial tissue. At the cellular level,cornification is characterised by:

  • production of keratin
  • production of small proline-rich (SPRR) proteins and transglutaminase which eventually form acornified cell envelope beneath the plasma membrane
  • terminal differentiation
  • loss of nuclei and organelles, in the final stages of cornification

Metabolism ceases, and the cells are almost completely filled by keratin. During the process of epithelial differentiation, cells become cornified as keratin protein is incorporated into longer keratin intermediate filaments. Eventually the nucleus and cytoplasmic organelles disappear, metabolism ceases and cells undergo aprogrammed death as they become fully keratinized. In many other cell types, such as cells of the dermis, keratin filaments and other intermediate filaments function as part of the cytoskeleton to mechanically stabilize the cell against physical stress. It does this through connections to desmosomes, cell–cell junctional plaques, and hemidesmosomes, cell-basement membrane adhesive structures.

Cells in the epidermis contain a structural matrix of keratin, which makes this outermost layer of the skin almost waterproof, and along with collagen and elastin gives skin its strength. Rubbing and pressure cause thickening of the outer, cornified layer of the epidermis and form protective calluses, which are useful for athletes and on the fingertips of musicians who play stringed instruments. Keratinized epidermal cells are constantly shed and replaced.

These hard, integumentary structures are formed by intercellular cementing of fibers formed from the dead, cornified cells generated by specialized beds deep within the skin. Hair grows continuously and feathers molt and regenerate. The constituent proteins may be phylogenetically homologous but differ somewhat in chemical structure and supermolecular organization. The evolutionary relationships are complex and only partially known. Multiple genes have been identified for the β-keratins in feathers, and this is probably characteristic of all keratins.

Silk

[edit]
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Thesilkfibroins produced byinsects andspiders are often classified as keratins, though it is unclear whether they are phylogenetically related to vertebrate keratins.

Silk found in insectpupae, and inspider webs and egg casings, also has twisted β-pleated sheets incorporated into fibers wound into larger supermolecular aggregates. The structure of thespinnerets on spiders' tails, and the contributions of their interiorglands, provide remarkable control of fastextrusion. Spider silk is typically about 1 to 2 micrometers (μm) thick, compared with about 60 μm for human hair, and more for some mammals. Thebiologically andcommercially useful properties ofsilk fibers depend on the organization of multiple adjacent protein chains into hard,crystalline regions of varying size, alternating with flexible,amorphous regions where the chains arerandomly coiled.[30] A somewhat analogous situation occurs withsyntheticpolymers such asnylon, developed as a silk substitute. Silk from thehornetcocoon contains doublets about 10 μm across, with cores and coating, and may be arranged in up to 10 layers, also in plaques of variable shape. Adult hornets also use silk as aglue, as do spiders.

Clinical significance

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Abnormal growth of keratin can occur in a variety of conditions includingkeratosis,hyperkeratosis andkeratoderma.

Mutations in keratin gene expression can lead to, among others:

Several diseases, such asathlete's foot andringworm, are caused byinfectious fungi that feed on keratin.[33]

Keratin is highly resistant to digestive acids if ingested.Cats regularly ingest hair as part of theirgrooming behavior, leading to the gradual formation ofhairballs that may be expelled orally or excreted. In humans,trichophagia may lead toRapunzel syndrome, an extremely rare but potentially fatal intestinal condition.

Diagnostic use

[edit]

Keratin expression is helpful in determining epithelial origin inanaplastic cancers. Tumors that express keratin includecarcinomas,thymomas,sarcomas andtrophoblastic neoplasms. Furthermore, the precise expression-pattern of keratin subtypes allows prediction of the origin of the primary tumor when assessingmetastases. For example,hepatocellular carcinomas typically express CK8 and CK18, andcholangiocarcinomas express CK7, CK8 and CK18, while metastases ofcolorectal carcinomas express CK20, but not CK7.[34]

See also

[edit]

References

[edit]
  1. ^OED 2nd edition, 1989 as/ˈkɛrətɪn/
  2. ^Entry "keratin"Archived 2013-05-09 at theWayback Machine inMerriam-Webster Online DictionaryArchived 2017-09-22 at theWayback Machine.
  3. ^Fraser, R.D.B. (1972).Keratins: Their composition, structure and biosynthesis. Bannerstone House: Charles C Thomas. pp. 3–6.ISBN 978-0-398-02283-9.
  4. ^abWang, Bin (2016)."Keratin: Structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration".Progress in Materials Science.76:229–318.doi:10.1016/j.pmatsci.2015.06.001.Archived from the original on 2022-09-19. Retrieved2019-07-03.
  5. ^Nasoori, Alireza (2020)."Formation, structure, and function of extra-skeletal bones in mammals".Biological Reviews.95 (4):986–1019.doi:10.1111/brv.12597.PMID 32338826.S2CID 216556342.
  6. ^"Keratin".Webster's Online Dictionary. 22 May 2023.Archived from the original on 1 May 2021. Retrieved9 August 2018.
  7. ^Vincent, Julian F.V; Wegst, Ulrike G.K (July 2004). "Design and mechanical properties of insect cuticle".Arthropod Structure & Development.33 (3):187–199.Bibcode:2004ArtSD..33..187V.doi:10.1016/j.asd.2004.05.006.PMID 18089034.
  8. ^Tombolato, Luca; Novitskaya, Ekaterina E.; Chen, Po-Yu; Sheppard, Fred A.; McKittrick, Joanna (February 2010). "Microstructure, elastic properties and deformation mechanisms of horn keratin".Acta Biomaterialia.6 (2):319–330.doi:10.1016/j.actbio.2009.06.033.PMID 19577667.
  9. ^"Keratin".VEDANTU. Retrieved2022-01-07.[permanent dead link‍]
  10. ^Hickman, Cleveland Pendleton; Roberts, Larry S.; Larson, Allan L. (2003).Integrated principles of zoology. Dubuque, IA: McGraw-Hill. p. 538.ISBN 978-0-07-243940-3.
  11. ^Kreplak, L.; Doucet, J.; Dumas, P.; Briki, F. (July 2004)."New Aspects of the α-Helix to β-Sheet Transition in Stretched Hard α-Keratin Fibers".Biophysical Journal.87 (1):640–647.Bibcode:2004BpJ....87..640K.doi:10.1529/biophysj.103.036749.PMC 1304386.PMID 15240497.
  12. ^Alibardi, Lorenzo (September 2016). "Sauropsids Cornification is Based on Corneous Beta-Proteins, a Special Type of Keratin-Associated Corneous Proteins of the Epidermis".Journal of Experimental Zoology Part B: Molecular and Developmental Evolution.326 (6):338–351.Bibcode:2016JEZB..326..338A.doi:10.1002/jez.b.22689.PMID 27506161.
  13. ^Moll, Roland; Divo, Markus; Langbein, Lutz (June 2008)."The human keratins: biology and pathology".Histochemistry and Cell Biology.129 (6):705–733.doi:10.1007/s00418-008-0435-6.PMC 2386534.PMID 18461349.
  14. ^abSchweizer J, Bowden PE, Coulombe PA, et al. (July 2006)."New consensus nomenclature for mammalian keratins".J. Cell Biol.174 (2):169–74.doi:10.1083/jcb.200603161.PMC 2064177.PMID 16831889.
  15. ^"GeneCards - Human Genes | Gene Database".Archived from the original on 2023-05-13. Retrieved2023-05-08.
  16. ^Hanukoglu, Israel; Fuchs, Elaine (November 1982)."The cDNA sequence of a human epidermal keratin: Divergence of sequence but conservation of structure among intermediate filament proteins".Cell.31 (1):243–252.doi:10.1016/0092-8674(82)90424-x.PMID 6186381.S2CID 35796315.Archived from the original on 2021-01-26. Retrieved2019-07-03.
  17. ^abcHanukoglu, Israel; Fuchs, Elaine (July 1983)."The cDNA sequence of a type II cytoskeletal keratin reveals constant and variable structural domains among keratins".Cell.33 (3):915–924.doi:10.1016/0092-8674(83)90034-x.PMID 6191871.S2CID 21490380.Archived from the original on 2021-01-26. Retrieved2019-07-03.
  18. ^Lee, Chang-Hun; Kim, Min-Sung; Chung, Byung Min; Leahy, Daniel J; Coulombe, Pierre A (July 2012)."Structural basis for heteromeric assembly and perinuclear organization of keratin filaments".Nature Structural & Molecular Biology.19 (7):707–715.doi:10.1038/nsmb.2330.PMC 3864793.PMID 22705788.
  19. ^"Type II Keratin - an overview | ScienceDirect Topics".www.sciencedirect.com.Archived from the original on 2023-03-28. Retrieved2023-03-28.
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  21. ^Hanukoglu, Israel; Ezra, Liora (January 2014)."Proteopedia entry: Coiled-coil structure of keratins: Multimedia in Biochemistry and Molecular Biology Education".Biochemistry and Molecular Biology Education.42 (1):93–94.doi:10.1002/bmb.20746.PMID 24265184.S2CID 30720797.
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External links

[edit]
Wikisource has the text of the 1920Encyclopedia Americana articleKeratin.
Extracellular
matrix
Collagen
Fibril forming
Other
Enzymes
Laminin
Other
Other
Human
Microfilaments
andABPs
Myofilament
Actins
Myosins
Other
Other
Intermediate
filaments
Type 1/2
(Keratin,
Cytokeratin)
Epithelial keratins
(soft alpha-keratins)
Hair keratins
(hard alpha-keratins)
Ungrouped alpha
Not alpha
Type 3
Type 4
Type 5
Microtubules
andMAPs
Tubulins
MAPs
Kinesins
Dyneins
Microtubule organising proteins
Microtubule severing proteins
Other
Catenins
Membrane
Other
Nonhuman
Authority control databases: NationalEdit this at Wikidata
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