Dynamic Light Scattering and Circular Dichroism Studies on Heat-Induced Gelation of Hard-Keratin Protein Aqueous Solutions

Abstract

Animal hairs consist of aggregates of dead cells filled with keratin protein gel. We succeeded in preparing water-soluble hard-keratin proteins and reconstructing the keratin gels by heat-induced disulfide linkages in vitro. Here, the roles of intermolecular hydrophobic interaction and disulfide bonding between the proteins in the gel were discussed. Water-soluble keratin proteins consisting of mixtures of type I ( approximately 48 kDa) and type II ( approximately 61 kDa) were prepared from wool fibers as S-carboxymethyl alanyl disulfide keratin (CMADK). The gelation was achieved by heating an aqueous solution containing at least 0.8 wt % CMADK at 100 degrees C. CMADK solutions with different urea or N-ethylmaleimide concentrations or pH were exposed to dynamic light scattering (DLS) and circular dichroism (CD). DLS clarified the gelation point of CMADK solutions and provided information on the changes in keratin cluster size. DLS suggested two types of gelation mechanism. One was the regenerated chemical disulfide bonding between keratins from CMAD parts of chains. After the gel formed, this bond became important to maintain the gel structure. The other was the physical assembly due to hydrophobic interaction between alpha-helix parts of keratin chains. This hydrophobic assembly also played an important role during gelation. CD confirmed a conformational change in the keratin protein, resulting heat-induced gelation. CD clarified the relationship between keratin protein conformation and gelation, i.e., a rodlike conformation with many alpha-helix structures was necessary to associate keratin chains and form a gel network.

Keratin hydrogels support the sustained release of bioactive ciprofloxacin

“…In contrast, hydrophobic interactions do not appear to play a significant role in maintaining the interaction between ciprofloxacin and keratose in the gel state. We do note that the application of 1 M NaCl slowed the rate of keratose release while application of 8 M urea increased the rate of keratose release from the hydrogels as measured by DC protein assay, indicating the role of hydrophobic interactions in maintaining the assembly of keratose proteins necessary for gel formation 41, 42. Ciprofloxacin is a polar molecule and has been reported to bind with the phosphate groups of DNA 43.…”

A Review of Keratin-Based Biomaterials for Biomedical Applications

“…First, extracted keratin proteins have an intrinsic ability to self-assemble and polymerize into porous, fibrous scaffolds. The spontaneous self-assembly of keratin solutions has been studied extensively at both the microscale [40,41,42] and macroscale levels [43]. This phenomenon of self-assembly is evident in the highly conserved superstructure of the hair fiber and, when processed correctly, is responsible for the reproducible architecture, dimensionality and porosity of keratin-based materials.…”

Modulation of keratin in adhesion, proliferation, adipogenic, and osteogenic differentiation of porcine adipose‐derived stem cells

“…Keratin is a family of structural proteins that can be isolated from epithelial tissues, nails, hooves, and hair. Preparations of keratin, in order to make keratin‐based scaffolds in various sizes and geometries (for example, porous or fibrous scaffold) with its intrinsic ability, have been investigated in the relevant fields such as biomaterials, tissue engineering, and regenerative medicine . Keratin‐based materials are suitable for biomedical applications for two reasons: (1) keratin derived from different sources (for example, wool or human hair) has been shown to preserve cell binding motifs including leucine‐aspartic acid‐valine (LDV) and glutamic acid‐aspartic acid‐serine (EDS) binding sites, enabling mammalian cells to attach onto keratin‐treated surfaces or keratin‐based scaffolds via protein–ligand interactions; and, (2) keratin is one of the intermediate filaments involved in regulating cellular behaviors (for example, migration, adhesion, and proliferation) .…”