The three-dimensional structure of trichocyte (hard alpha-) keratin intermediate filaments: the nature of the repeating unit

Effect of mutations on the hydrophobic interactions of the hierarchical molecular structure and mechanical properties of epithelial keratin 1/10

Human epithelial keratin is an intermediate filament protein that serves as a backbone to maintain the stability of the cell nucleus and mechanical stability of the whole cells. The present study focused on two point mutations, F231L and S233L, of the 1B domain of keratin K 1/10 related to the rare genetic skin disease palmoplantar keratoderma (PPK). We used molecular dynamics simulation to study the effects of the mutations on various hierarchical structures, including heterodimers, tetramers, and octamers of the K1/10 1B domain at the atomic scale. The initial results demonstrated that the wild type and mutant proteins were highly similar at the dimer level but had different microstructures and mechanics at a higher-level assembly. A decrease in the hydrophobic interactions and hydrogen bonds at the terminus resulted in weakened mechanical properties of the tetramer and octamer of the F231L mutant. The asymmetrical structure of the S233L tetramer with an uneven distribution of the hydrogen bonds decreased its mechanical properties. However, the S233L mutation provided extra hydrophobic interactions between these mutated amino acid residues in the octamer, leading to improved mechanical properties. The results of the present study provided a deeper understanding of how the differences in point mutations induced the changes in the configuration and mechanical properties at the molecular scale. The differences in these properties may influence keratin assembly at the microscopic scale and ultimately cause diseases at the macroscopic scale.

Porosity at Different Structural Levels in Human and Yak Belly Hair and Its Effect on Hair Dyeing

Yak belly hair was proposed as a cheap substitute for human hair for the development of hair dyes, as its chemical composition closely resembles human hair in Raman spectroscopy. The absence of melanin in yak belly hair also leads to a strong reduction of fluorescence in Raman measurements, which is advantageous for the investigation of the effectivity of hair dyes. To assess the suitability for replacing human hair, we analyzed similarities and differences of both hair types with a variety of methods: Raman spectroscopy, to obtain molecular information; small-angle X-ray scattering to determine the nanostructure, such as intermediate filament distance, distance of lipid layers and nanoporosity; optical and scanning electron microscopy of surfaces and cross sections to determine the porosity at the microstructural level; and density measurements and tensile tests to determine the macroscopic structure, macroporosity and mechanical properties. Both types of hair are similar on a molecular scale, but differ on other length scales: yak belly hair has a smaller intermediate filament distance on the nanoscale. Most striking is a higher porosity of yak belly hair on all hierarchical levels, and a lower Young’s modulus on the macroscale. In addition to the higher porosity, yak belly hair has fewer overlapping scales of keratin, which further eases the uptake of coloring. This makes, on the other hand, a comparison of coloring processes difficult, and limits the usefulness of yak belly hair as a substitute for human hair.

beta-Keratins in crocodiles reveal amino acid homology with avian keratins

The DNA sequences encoding beta-keratin have been obtained from Marsh Mugger (Crocodylus palustris) and Orinoco Crocodiles (Crocodylus intermedius). Through the deduced amino acid sequence, these proteins are rich in glycine, proline and serine. The central region of the proteins are composed of two beta-folded regions and show a high degree of identity with beta-keratins of aves and squamates. This central part is thought to be the site of polymerization to build the framework of beta-keratin filaments. It is believed that the beta-keratins in reptiles and birds share a common ancestry. Near the C-terminal, these beta-keratins contain a peptide rich in glycine-X and glycine-X-X, and the distinctive feature of the region is some 12-amino acid repeats, which are similar to the 13-amino acid repeats in chick scale keratin but absent from avian feather keratin. From our phylogenetic analysis, the beta-keratins in crocodile have a closer relationship with avian keratins than the other keratins in reptiles.