Keratins: Difference between revisions
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Note: This entry on keratins has been | {{BAMBED | ||
|DATE=September 12, 2013 | |||
|OLDID=1842003 | |||
|BAMBEDDOI=10.1002/bmb.20746 | |||
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Note: This entry on keratins has been published in Biochem. Mol. Biol. Educ.<ref>PMID:24265184</ref>. Please cite it as Biochem. Mol. Biol. Educ. 42:93-4, 2014. | |||
Keratin is the name given to a large family of homologous proteins that have a filamentous (fibrous) structure. These proteins are expressed in epithelial cells and in epidermal cells where they are assembled forming cytoskeletal structures within the cell and epidermal derivatives such as hair, nail and horn <ref>PMID:18461349</ref>. | '''Keratin''' is the name given to a large family of homologous proteins that have a filamentous (fibrous) structure. These proteins are expressed in epithelial cells and in epidermal cells where they are assembled forming cytoskeletal structures within the cell and epidermal derivatives such as hair, nail and horn <ref>PMID:18461349</ref>. | ||
The keratins represent the largest branch within the super-family of intermediate-filament (IF) proteins <ref name="Godsel-2008">PMID:18083519</ref> <ref>PMID:19587451</ref>. Keratins are grouped into two families termed as type I and type II keratins based on their sequence homology <ref name="Hanukoglu-1983">PMID:6191871</ref>. Similarly, other IF proteins are also grouped into families termed consecutively as types III, IV, V and VI IF proteins, based on their sequence homology <ref>PMID:8982454</ref>. These families include desmin, vimentin, neurofilament protein and GFAP that are expressed in specific tissues and cell types <ref name="Godsel-2008" />. The IF family of lamins are located on the nuclear lamina and are ubiquitously expressed <ref name="Godsel-2008" />. | The keratins represent the largest branch within the super-family of intermediate-filament (IF) proteins <ref name="Godsel-2008">PMID:18083519</ref> <ref>PMID:19587451</ref>. Keratins are grouped into two families termed as type I and type II keratins based on their sequence homology <ref name="Hanukoglu-1983">PMID:6191871</ref>. Similarly, other IF proteins are also grouped into families termed consecutively as types III, IV, V and VI IF proteins, based on their sequence homology <ref>PMID:8982454</ref>. These families include desmin, vimentin, neurofilament protein and GFAP that are expressed in specific tissues and cell types <ref name="Godsel-2008" />. The IF family of lamins are located on the nuclear lamina and are ubiquitously expressed <ref name="Godsel-2008" />. | ||
See [[Keratin (hebrew)]]. | |||
==Intermediate filaments== | ==Intermediate filaments== | ||
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Both microfilaments and microtubules are assembled from globular subunits of actin and tubulin respectively. In contrast, intermediate filaments (IFs) are composed of proteins that have a long fibrous structure that results from long stretches of alpha helical domains. | Both microfilaments and microtubules are assembled from globular subunits of actin and tubulin respectively. In contrast, intermediate filaments (IFs) are composed of proteins that have a long fibrous structure that results from long stretches of alpha helical domains. | ||
The basic building block of each intermediate filament is a dimer of a coiled-coil pair of IF proteins. Each keratin filament is assembled as a hetero-dimer of a type I keratin coiled together with a type II keratin. <ref name="Hanukoglu-1983">PMID:6191871</ref>. Other types of IFs are mostly composed of homo-dimers <ref name="Godsel-2008" />. | The basic building block of each intermediate filament is a dimer of a coiled-coil pair of IF proteins (see [[Coiled coil]]). Each keratin filament is assembled as a hetero-dimer of a type I keratin coiled together with a type II keratin. <ref name="Hanukoglu-1983">PMID:6191871</ref>. Other types of IFs are mostly composed of homo-dimers <ref name="Godsel-2008" />. | ||
==Primary structures of keratins== | ==Primary structures of keratins== | ||
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==Bonds that hold the coiled-coil structure== | ==Bonds that hold the coiled-coil structure== | ||
<Structure load='3TNU' size=' | <Structure load='3TNU' size='400' frame='' align='right' caption='Fig. 2. Crystal structure of the 2B helical domain of coiled-coil dimer of type I keratin K14 (chain A) and type II keratin K5 (chain B) (residues Ser332-Gly421 of K14 and Thr382-Gly476 of K5). PDB ID: 3tnu. | ||
Please click the green colored links in the text in order to view highlighted features of the structure.' /> | Please click the green colored links in the text in order to view highlighted features of the structure.' /> | ||
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It can be seen that the hydrophobic residues are predominantly located in the interface between the two chains and essentially occupy the space between these chains. Thus, hydrophobic residues that can associate with one another in the aqueous environment of cell are the main points of contact between the chains in the coiled-coil. | It can be seen that the hydrophobic residues are predominantly located in the interface between the two chains and essentially occupy the space between these chains. Thus, hydrophobic residues that can associate with one another in the aqueous environment of cell are the main points of contact between the chains in the coiled-coil. | ||
As the two chains of keratins are intertwined in parallel, the contact points along the entire coiled-coil | As the two chains of keratins are intertwined in parallel, the contact points along the entire coiled-coil represent a seam along the two proteins. Coiled-coil structures are found in many types of proteins. In two-chained coiled-coil proteins hydrophobic residues appear in a periodic pattern that has been named a heptad-repeat <ref name="Woolfson-2005">PMID:15837514</ref>. In a regular α-helix there are 3.6 residues per turn of the helix. In a left-handed coiled-coil there are 3.5 residues per turn. Thus, in a two chained coiled-coil there is a repeat pattern of seven residues that are represented by the letters a-b-c-d-e-f-g. Residues a and d in this pattern are hydrophobic. These two residues define a hydrophobic flank for each protein. This periodic pattern was first reported on both type I and type II wool keratins <ref name="PMID697726">PMID:697726</ref> and later observed on cytoskeletal keratins as well <ref name="Hanukoglu-1983" />. The crystal structures of the 2B segment of keratins K14 and K5 provided final confirmation for the role of these hydophobic residues in coiled-coil formation <ref name="Lee-2012" />. | ||
==3D structure of keratin== | ==3D structure of keratin== | ||
Updated on {{REVISIONDAY2}}-{{MONTHNAME|{{REVISIONMONTH}}}}-{{REVISIONYEAR}} | |||
[[3tnu]] - hKRT14 residues 295-422 + hKRT5 residues 350-477 - | [[4zry]], [[6e2j]], [[6uui]] – hKRT1 coil 2B domain + hKRT10 coil 2B domain – human<br /> | ||
[[6ec0]] – hKRT10 coil 1B domain + hKRT1 coil 1B domain <br /> | |||
[[6e2j]] – hKRT10 coil 1B domain + hKRT1 coil 1B domain (mutant)<br /> | |||
[[6ec0]] – hKRT1 coil 1B domain + hKRT10 coil 1B domain <br /> | |||
[[3tnu]] - hKRT14 residues 295-422 + hKRT5 residues 350-477 <br /> | |||
[[6jfv]] - hKRT14 residues 327-421 (mutant) + hKRT5 residues 379-476 <br /> | |||
[[3asw]], [[4f1z]] - hKRT10 peptide + clumping factor B<br /> | [[3asw]], [[4f1z]] - hKRT10 peptide + clumping factor B<br /> | ||