Beta-keratin ( β-keratin) is a structural protein found in the epidermis of , , and Pangolin.
Structure
Beta-keratins were named due to their composition of stacked
in the epidermal
stratum corneum, distinguishing them from
, which are intermediate-filament proteins rich in
alpha helices.
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."
Function
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.
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.
Evolution
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.
Fossil evidence
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.
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.
This highlights the potential for false positives in immunohistochemical analyses of fossilized remains.
See Also
External links
