Keratins are structural proteins that are abundant in
human skin,
nails, and hair, where they provide mechanical strength. In the present
study, we investigate the molecular mobilities and structures of three
keratin-rich materials with clearly different mechanical properties:
nails, stratum corneum (upper layer of epidermis), and keratinocytes
(from lower layer of epidermis). We use solid-state NMR on natural-abundance13C to characterize small changes in molecular dynamics in
these biological materials with close to atomistic resolution. One
strong advantage of this method is that it detects small fractions
of mobile components in a molecularly complex material while it simultaneously
gives information on the rigid components in the very same sample.
The molecular mobility can be linked to mechanical material properties
in different conditions, including hydration or exposure to osmolytes
or organic solvents. Importantly, the study revealed that the response
to both hydration and addition of urea is clearly different for the
nail keratin compared to the stratum corneum keratin. The comparative
examination of these materials may provide a better understanding
of skin diseases originating from keratin malfunction and contributes
to the design and development of new materials.