beta-keratin

Beta-keratins were named due to their composition of stacked beta sheets in the epidermal stratum corneum, distinguishing them from alpha-keratins, which are intermediate-filament proteins rich in alpha helices.{{cite journal | vauthors = Calvaresi M, Eckhart L, Alibardi L | title = The molecular organization of the beta-sheet region in Corneous beta-proteins (beta-keratins) of sauropsids explains its stability and polymerization into filaments | journal = Journal of Structural Biology | volume = 194 | issue = 3 | pages = 282–291 | date = June 2016 | pmid = 26965557 | doi = 10.1016/j.jsb.2016.03.004 }} Recent studies suggest that the term keratin should be restricted to alpha-keratins. As a result, "beta-keratins" are now often referred to as "corneous beta-proteins" or "keratin-associated beta-proteins."{{cite journal | vauthors = Alibardi L | title = Cornification in reptilian epidermis occurs through the deposition of keratin-associated beta-proteins (beta-keratins) onto a scaffold of intermediate filament keratins | journal = Journal of Morphology | volume = 274 | issue = 2 | pages = 175–193 | date = February 2013 | pmid = 23065677 | doi = 10.1002/jmor.20086 | s2cid = 23739887 }}

β-keratins contribute significantly to the rigidity and waterproofing of reptilian skin by being impregnated into the stratum corneum. This provides protection against desiccation and enhances durability in terrestrial environments. In birds, β-keratin is found in the scales, beaks, claws, and feathers. Phylogenetic studies indicate that feather β-keratins evolved from scale β-keratins.{{cite journal | vauthors = Greenwold MJ, Sawyer RH | title = Genomic organization and molecular phylogenies of the beta (beta) keratin multigene family in the chicken (Gallus gallus) and zebra finch (Taeniopygia guttata): implications for feather evolution | journal = BMC Evolutionary Biology | volume = 10 | pages = 148 | date = May 2010 | issue = 1 | pmid = 20482795 | pmc = 2894828 | doi = 10.1186/1471-2148-10-148 | doi-access = free | bibcode = 2010BMCEE..10..148G }} The scale β-keratins form the basal group in avians, followed by claw β-keratin genes, with further recombination leading to new feather and feather-like β-keratin genes. These evolutionary patterns correlate with genomic loci.{{cite journal | vauthors = Greenwold MJ, Sawyer RH | title = Linking the molecular evolution of avian beta (β) keratins to the evolution of feathers | journal = Journal of Experimental Zoology. Part B, Molecular and Developmental Evolution | volume = 316 | issue = 8 | pages = 609–616 | date = December 2011 | pmid = 21898788 | doi = 10.1002/jez.b.21436 | bibcode = 2011JEZB..316..609G }}

Changes in β-keratins may have influenced the evolution of powered flight. Molecular dating suggests that avian β-keratin genes began diverging from their crocodilian relatives approximately 216 million years ago. However, feather β-keratins did not begin differentiating until around 125 million years ago, coinciding with the adaptive radiation of birds during the Cretaceous. Modern feather β-keratins exhibit increased elasticity, which may have contributed to the development of flight.

Feathered non-avian dinosaurs, such as Anchiornis and Archaeopteryx, likely possessed avian β-keratins but lacked the specialized feather β-keratins, raising questions about their flight capabilities.{{cite journal | vauthors = Nudds RL, Dyke GJ | title = Narrow primary feather rachises in Confuciusornis and Archaeopteryx suggest poor flight ability | journal = Science | volume = 328 | issue = 5980 | pages = 887–889 | date = May 2010 | pmid = 20466930 | doi = 10.1126/science.1188895 | s2cid = 12340187 | bibcode = 2010Sci...328..887N }}

The small alvarezsaurid dinosaur Shuvuuia deserti was once believed to have a feather-like skin covering composed of β-keratin. An immunohistochemical analysis by Schweitzer et al. (1999) initially supported this conclusion.{{cite journal | vauthors = Schweitzer MH, Watt JA, Avci R, Knapp L, Chiappe L, Norell M, Marshall M | title = Beta-keratin specific immunological reactivity in feather-like structures of the cretaceous alvarezsaurid, Shuvuuia deserti | journal = The Journal of Experimental Zoology | volume = 285 | issue = 2 | pages = 146–57 | date = August 1999 | pmid = 10440726 | doi = 10.1002/(SICI)1097-010X(19990815)285:2<146::AID-JEZ7>3.0.CO;2-A| bibcode = 1999JEZ...285..146S | url = }} However, subsequent research by Saitta et al. (2018) refuted this claim, demonstrating that the fibers analyzed consisted of inorganic calcium phosphate rather than β-keratin.{{cite journal | vauthors = Saitta ET, Fletcher I, Martin P, Pittman M, Kaye TG, True LD, Norell MA, Abbott GD, Summons RE, Penkman K, Vinther J | title = Preservation of feather fibers from the Late Cretaceous dinosaur Shuvuuia deserti raises concern about immunohistochemical analyses on fossils. | journal = Organic Geochemistry | date = November 2018 | volume = 125 | pages = 142–151 | doi = 10.1016/j.orggeochem.2018.09.008 | bibcode = 2018OrGeo.125..142S | url = https://eprints.whiterose.ac.uk/137093/1/Saitta_et_al_feather_fibres_OG_AAM.docx | hdl = 1721.1/125319 | hdl-access = free }} This highlights the potential for false positives in immunohistochemical analyses of fossilized remains.

• Keratin
• Feathered dinosaurs
• Sauropsida

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• {{MeshName|beta-Keratins}}

{{Cytoskeletal proteins}}

Category:Keratins