Keratins: Difference between revisions
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Human genome sequencing revealed that type I and type II keratin genes are located in two clusters each of which includes 27 genes on chromosome 17q21 and on chromosome 12q13 respectively <ref name="PMID15085952" /> <ref>PMID:17428470</ref>. The juxtaposed location of the genes indicate that these gene clusters evolved by a series of gene duplication events. | Human genome sequencing revealed that type I and type II keratin genes are located in two clusters each of which includes 27 genes on chromosome 17q21 and on chromosome 12q13 respectively <ref name="PMID15085952" /> <ref>PMID:17428470</ref>. The juxtaposed location of the genes indicate that these gene clusters evolved by a series of gene duplication events. | ||
Determination of the sequences of type I and type keratins revealed that the two types of keratins have a central ~ | Determination of the sequences of type I and type keratins revealed that the two types of keratins have a central ~310 residue long segment that share ~30% homology, but the amino and carboxy terminal regions of these proteins show great diversity <ref name="PMID6186381" />. Consistent with the initial observations, sequencing of keratins and other intermediate filament proteins showed that all IF proteins have a conserved central domain and widely divergent amino and carboxy terminal regions <ref>PMID: 17521629</ref>. | ||
Sequencing and two dimensional gel electrophoresis of the complete family of keratins revealed that the type I and type II keratins differ in their size and isoelectric points <ref name="PMID19422428">PMID:19422428</ref> <ref>PMID:18461349</ref>. Type I keratins are generally smaller (average length 460 aa's), and acidic (isoelectric point 4.4-5.4), while type II keratins are longer (average length 545 aa's) and basic (isoelectric point 5-8.3). As noted, the size differences among keratins result from differences in the amino and carboxy terminals of the proteins <ref name="PMID6191871" />. | Sequencing and two dimensional gel electrophoresis of the complete family of keratins revealed that the type I and type II keratins differ in their size and isoelectric points <ref name="PMID19422428">PMID:19422428</ref> <ref>PMID:18461349</ref>. Type I keratins are generally smaller (average length 460 aa's), and acidic (isoelectric point 4.4-5.4), while type II keratins are longer (average length 545 aa's) and basic (isoelectric point 5-8.3). As noted, the size differences among keratins result from differences in the amino and carboxy terminals of the proteins <ref name="PMID6191871" />. | ||
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* Hydrogen bonds between suitable groups. | * Hydrogen bonds between suitable groups. | ||
In the 2B domains of keratins type I K14 and type II K5 shown in Fig. 3, there are two and a single cysteine respectively. These cysteines are far apart and cannot form disulfide bridges. Click here to see the locations of the Cys in Fig. 3. Thus, disulfide bridges cannot be responsible for the binding of K14 and K5. | In the 2B domains of keratins type I K14 and type II K5 shown in Fig. 3, there are two and a single cysteine respectively. These cysteines are far apart and cannot form disulfide bridges. | ||
* Click here to see the locations of the Cys in Fig. 3. | |||
Thus, disulfide bridges cannot be responsible for the binding of K14 and K5. | |||
The second option is ionic bonds, or salt bridges between the two keratins. | The second option is ionic bonds, or salt bridges between the two keratins. | ||
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* Click here to see the basic residues, Arg and Lys. | * Click here to see the basic residues, Arg and Lys. | ||
Both acidic and basic residues are seen to protrude mostly towards the outside surface of the two keratins and hardly in the space between the two keratins. The contact surface between the two keratins in a coiled-coil | Both acidic and basic residues are seen to protrude mostly towards the outside surface of the two keratins and hardly in the space between the two keratins. The contact surface between the two keratins in a coiled-coil is located between the two keratins. Thus, the charged residues do not play a predominant role in the formation of the coiled-coil. In the K14-K5 dimer only 3-4 residues are involved in inter-strand interactions. Nonetheless, these residues are essential for normal function of keratin <ref name="PMID19422428" />. | ||
===Hydrophobic residues: Main points of contact between chains === | ===Hydrophobic residues: Main points of contact between chains === | ||