Structures of the ss-Keratin Filaments and Keratin Intermediate Filaments in the Epidermal Appendages of Birds and Reptiles (Sauropsids)

The epidermal appendages of birds and reptiles (the sauropsids) include claws, scales, and feathers. Each has specialized physical properties that facilitate movement, thermal insulation, defence mechanisms, and/or the catching of prey. The mechanical attributes of each of these appendages originate from its fibril-matrix texture, where the two filamentous structures present, i.e., the corneous ss-proteins (CBP or ss-keratins) that form 3.4 nm diameter filaments and the alpha-fibrous molecules that form the 7-10 nm diameter keratin intermediate filaments (KIF), provide much of the required tensile properties. The matrix, which is composed of the terminal domains of the KIF molecules and the proteins of the epidermal differentiation complex (EDC) (and which include the terminal domains of the CBP), provides the appendages, with their ability to resist compression and torsion. Only by knowing the detailed structures of the individual components and the manner in which they interact with one another will a full understanding be gained of the physical properties of the tissues as a whole. Towards that end, newly-derived aspects of the detailed conformations of the two filamentous structures will be discussed and then placed in the context of former knowledge.

Automated summary

Epidermal appendages of birds and reptiles, including claws, scales, and feathers, have specialized physical properties that facilitate movement, thermal insulation, defence mechanisms, and/or catching prey. The mechanical attributes of these appendages originate from their fibril-matrix texture, with corneous ss-proteins and keratin intermediate filaments providing much of the required tensile properties. Understanding the detailed structures of these components and how they interact with each other is crucial for comprehending the physical properties of these tissues.