Structural studies of keratin fibres and their protein-lipid matrix

Keratins are one of the most abundant proteins found in mammals. They possess intrinsic properties that are as a result of their extensive and complex molecular architecture. They are physicochemically and biomechanically robust. Their complex molecular assembly is what confers them their stability. For this reason understanding their internal structure could yield essential information regarding their function and properties. In addition, quantifiable changes detected in the structure could give rise to new insights that could be exploited in the dermatologic and cosmetic industries. Their ubiquitous nature means that the fundamental biophysical understanding, could aid in the development of analogous protein-based fibrous biomaterials for a wide range of purposes. Equilibrium and time-resolved x-ray diffraction along with multinuclear natural abundance NMR (1H and 13C) techniques have been utilised to study the effect various modifications have on the structure of keratin fibres, and their associated proteins and lipids. The core structural intermediate filament units have been analysed using x-ray diffraction. The molecular mobilities of the keratin protein networks have been investigated using solid-state NMR. The intermediate filaments, which make up the internal scaffolding of keratin fibres, were found to be extremely robust and this was ascertained through lateral and axial swelling experiments. With a range of modification, the sensitive detection of protein reduction and denaturing was quantified. The hydration of lithium bromide modified keratin was found to achieve large degrees of lateral swelling without protein degradation at equilibrium. Some key findings of the research include the cooperative behaviour of the intermediate filaments and their constituent α-helical proteins, these behaved analogously upon hydration. This was observed through time-resolved hydration experiments which were carried out for the first time on human keratin fibres. In addition, the amorphous intracellular matrix within keratin fibres displayed interesting and varied polymorphic behaviour. Furthermore, the presence of two distinct lipid bilayer domains has been detected: an intracellular domain and a cuticle domain. These core findings may be applicable to other fibrous proteins, detection of distal pathological pathways and the development of analogous bio-materials.