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Not to be confused with beta-carotene.

β-keratin or beta-keratin is rich in stacked β pleated sheets, in contrast to alpha-keratin, a fibrous protein rich in alpha helices.

β-keratin is found in reptiles.[1][2] It adds much more rigidity to reptilian skin than alpha-keratin does to mammalian skin.

β-keratin is impregnated into the stratum corneum of the reptilian skin, providing waterproofing and the prevention of desiccation.

In birds, scales, beaks, claws and feathers also contain β-keratin of the avian family. Phylogenetic studies of β-keratin sequences show that feather β-keratins evolved from scale β-keratins.[3] The scale β-keratins form the basal group in avians. Duplication and divergence events then led to claw β-keratin genes, and further recombination resulted in new feather and feather-like avian β-keratin genes. Evidence for these duplication events comes from the correlation of feather β-keratin clade structure with their genomic loci.[4]

Changes in β-keratins may have also influenced the development of powered flight. A recent study using molecular dating methods to link the evolution of β-keratin genes to that of feathers reveals that the avian β-keratin family began diverging from the crocodile family about 216 million years ago.[4] But the feather β-keratin family did not begin diverging until 125 million years ago, a date consistent with the adaptive radiation of birds during the Cretaceous. β-keratins found in modern feathers have increased elasticity, a factor that may have contributed to their role in flight.[4] Thus, the feathered ancestors of birds including Anchiornis and Archaeopteryx, whose flight capabilities have been questioned,[5] would have had avian, but not feather β-keratins.

The small alvarezsaurid dinosaur Shuvuuia deserti showed evidence of a featherlike skin covering. Analysis by Schweitzer et al. (1999) showed that these featherlike structures consisted of beta-keratin.[6]

References[edit]

  1. ^ Dalla Valle L, Nardi A, Belvedere P, Toni M, Alibardi L (July 2007). "Beta-keratins of differentiating epidermis of snake comprise glycine-proline-serine-rich proteins with an avian-like gene organization". Dev. Dyn. 236 (7): 1939–53. doi:10.1002/dvdy.21202. PMID 17576619. 
  2. ^ Dalla Valle L, Nardi A, Toffolo V, Niero C, Toni M, Alibardi L (February 2007). "Cloning and characterization of scale beta-keratins in the differentiating epidermis of geckoes show they are glycine-proline-serine-rich proteins with a central motif homologous to avian beta-keratins". Dev. Dyn. 236 (2): 374–88. doi:10.1002/dvdy.21022. PMID 17191254. 
  3. ^ Greenwold, M.J.; Sawyer, R.H. (2010). "Genomic organization and molecular phylogenies of the beta (β) keratin multigene family in the chicken (Gallus gallus) and zebra finch (Taeniopygia guttata): implications for feather evolution". BMC Evolutionary Biology 10. doi:10.1186/1471-2148-10-148. 
  4. ^ a b c Greenwold, M.J.; Sawyer, R.H. (2011). "Linking the molecular evolution of avian beta (β) keratins to the evolution of feathers". Journal of Experimental Zoology 316B: 609–616. doi:10.1002/jez.b.21436. 
  5. ^ Nudds, R.L.; Dyke, G.J. (14 May 2010). "Narrow Primary Feather Rachises in Confuciusornis and Archaeopteryx Suggest Poor Flight Ability". Science 328: 887–889. doi:10.1126/science.1188895. PMID 20466930. 
  6. ^ .Schweitzer, Mary Higby, Watt, J.A., Avci, R., Knapp, L., Chiappe, L, Norell, Mark A., Marshall, M. (1999). "Beta-Keratin Specific Immunological reactivity in Feather-Like Structures of the Cretaceous Alvarezsaurid, Shuvuuia deserti Journal of Experimental Biology (Mol Dev Evol) 255:146-157

External links[edit]

There are two main forms of keratin, alpha-keratin and beta-keratin. Alpha-keratin is seen in humans and other mammals, beta-keratin is present in birds and reptiles. Beta-keratin is harder than alpha-keratin. Structurally alpha-keratin have alpha-helical coiled coil structure while beta-keratin have twisted beta sheet structure.bIn the case of β-sheets, this allows sterically-unhindered hydrogen bonding between the amino and carboxyl groups of peptide bonds on adjacent protein chains, facilitating their close alignment and strong binding. Fibrous keratin molecules can twist around each other to form helical intermediate filaments.

SILK:- The secondary structure of silk is an example of the beta pleated sheet. In this structure, individual protein chains are aligned side-by-side with every other protein chain aligned in an opposite direction.The chains are antiparallel, with an alternating C → N orientation. The protein chains are held together by intermolecular hydrogen bonding, that is hydrogen bonding between amide groups of two separate chains. This intermolecular hydrogen bonding in the beta-pleated sheet is in contrast to the intramolecular hydrogen bonding in the alpha-helix.

The hydrogen on the amide of one protein chain is hydrogen bonded to the amide oxygen of the neighboring protein chain. The pleated sheet effect arises form the fact that the amide structure is planar while the "bends" occur at the carbon containing the side chain.

Fortunately, the "side" chain R groups in silk are not very bulky. The basic primary structure of silk consists of a six amino acid unit that repeats itself. The sequence where every other unit is glycine in silk is: -gly-ala-gly-ala-gly-ala-. Although glycine and alanine make up 75-80% of the amino acids in silk, another 10-15% is serine and the final 10% contain bulky side chains such as in tyr, arg, val, asp, and glu.


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Beta-keratin — Please support Wikipedia.
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41 news items

NBCNews.com

NBCNews.com
Thu, 11 Dec 2014 17:39:47 -0800

At least 13 of the penguins' genes were responsible for a single type of beta-keratin. That points to the importance of short, stiff, strong, densely packed feathers to prevent heat loss and repel water while swimming. Another gene, known as DSG1, has ...

Phys.Org

Phys.Org
Wed, 11 Feb 2015 07:27:14 -0800

Greenwold's co-author and postdoctoral adviser, professor Roger Sawyer, has spent over 30 years working with beta-keratin, and his work has helped differentiate among what has turned out to be many variations, some very subtle, on a main theme in ...

RedOrbit

RedOrbit
Thu, 12 Feb 2015 07:11:15 -0800

Greenwold's co-author and postdoctoral adviser, professor Roger Sawyer, has spent over 30 years working with beta-keratin, and his work has helped differentiate among what has turned out to be many variations, some very subtle, on a main theme in ...

Daily Mail

Daily Mail
Thu, 11 Dec 2014 11:25:54 -0800

They carry more genes for a particular type of beta keratin than any other bird and it is thought this is what allows them develop their thick plumage of short, stiff feathers that keep them warm. The scientists also discovered that penguins have a ...

Scientist (blog)

Scientist (blog)
Mon, 12 Jan 2015 10:56:15 -0800

Among the notable differences they found were 13 penguin genes encoding for beta-keratin proteins, the main component of feathers. These help create penguins' distinctive densely-packed wings that keep heat in and water out. Other clues to penguin ...

Big Country Homepage

Big Country Homepage
Thu, 27 Nov 2014 17:30:00 -0800

"Pumpkin has that beta keratin within it, also high in vitamin c. It is still considered a fruit, but it's not super sweet. Pumpkin pie is not necessarily a bad option unless it has a lot of sugar," says Armstrong. On the other hand, pecan and fruit ...

National Geographic

National Geographic
Fri, 10 Oct 2014 14:15:03 -0700

These weren't the same as the beta-keratin-coated scales of today's lizards and snakes, but analogous structures. Basically, pseudoscales. And additional finds, including body impressions, suggest that the bellies of early synapsids were dotted with ...

Science Codex

Science Codex
Sun, 14 Dec 2014 14:32:47 -0800

The genomes of modern birds tell a story of how they emerged and evolved after the mass extinction that wiped out dinosaurs and almost everything else 66 million years ago. That story is now coming to light, thanks to an ambitious international ...
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