Structure and Mechanical Properties of Human Trichocyte Keratin Intermediate Filament Protein

Keratin is a protein in the intermediate filament family
and the
key component of hair, nail, and skin. Here we report a bottom-up
atomistic model of the keratin dimer, using the complete human keratin
type k35 and k85 amino acid sequence. A detailed analysis of geometric
and mechanical properties through full-atomistic simulation with validation
against experimental results is presented. We introduce disulfide
cross-links in a keratin tetramer and compare the mechanical behavior
of the disulfide bonded systems with a system without disulfide bonds.
Disulfide bond results in a higher strength (20% increase) and toughness
(49% increase), but the system loses α-helical structures under
loading, suggesting that disulfide bonds play a significant role in
achieving the characteristic mechanical properties of trichocyte α-keratin.
Our study provides general insight into the effect of disulfide cross-link
on mechanical properties. Moreover, the availability of an atomistic
model of this protein opens the possibility to study the mechanical
properties of hair fibrils and other fibers from a bottom-up perspective.