Mapping the accessibility of the disulfide crosslink network in the wool fiber cortex

Abstract

The disulfide bond network within the cortex of mammalian hair has a critical influence on the physical and mechanical characteristics of the fiber. The location, pattern, and accessibility of free and crosslinked cysteines underpin the properties of this network, but have been very difficult to map and understand, because traditional protein extraction techniques require the disruption of these disulfide bonds. Cysteine accessibility in both trichocyte keratins and keratin associated proteins (KAPs) of wool was investigated using staged labeling, where reductants and chaotropic agents were used to expose cysteines in a stepwise fashion according to their accessibility. Cysteines thus exposed were labeled with distinguishable alkylation agents. Proteomic profiling was used to map peptide modifications and thereby explore the role of KAPs in crosslinking keratins. Labeled cysteines from KAPs were detected when wool was extracted with reductant only. Among them were sequences from the end domains of KAPs, indicating that those cysteines were easily accessible in the fiber and could be involved in forming interdisulfide linkages with keratins or with other KAPs. Some of the identified peptides were from the rod domains of Types I and II keratins, with their cysteines positioned on the exposed surface of the α-helix. Peptides were also identified from keratin head and tail domains, demonstrating that they are not buried within the filament structure and, hence, have a possible role in forming disulfide linkages. From this study, a deeper understanding of the accessibility and potential reactivity of cysteine residues in the wool fiber cortex was obtained.

Cross‐linking reactions in food proteins and proteomic approaches for their detection

“…The former ones are generated by the catalytic action of lysyl oxidases (Lucero & Kagan, 2006). Lastly, keratin heteropolymers from epithelial cells present in foods of animal origin were shown to be stabilized by inter‐chain disulfide bonds (Deb‐Choudhury et al, 2015). Only a few of the above‐mentioned studies on these polymeric proteins were performed using modern proteomic approaches (Eyre et al, 2019; Hedtke et al, 2019; Schräder et al, 2018), while most were conducted by combining chromatographic procedures with Edman degradation protocols (Brown‐Augsburger et al, 1995; Gerber & Anwar, 1975; Veraverbeke & Delcour, 2002).…”

Wanted, dead and alive: Why a multidisciplinary approach is needed to unlock hair treatment potential

“…Disulphide bonds determine curvature, stability and texture; hence, manipulation of disulphides forms the basis of structural modifications such as perming and rebonding . However, clear understanding of protein interconnectedness is in its early stages and is crucial because network alteration by environmental stresses will be determined by the basal organization laid down during hair development. Connecting structural features to single fibre properties is a challenge that will rely heavily on mathematical models and robust data on variation at different molecular scales …”

Characterizing historical textiles and clothing with proteomics

“…In sheep wool, the cortex, whose macrofibril architecture defines crimp and coarseness of fibers, is organized into three cell types: paracortex, orthocortex, and mesocortex [21][22]. The macrofibrils are composed of intermediate filaments (IFs) of trichocyte keratins arranged longitudinally, cross-linked to structurally irregular keratin-associated proteins (KAPs) that compose the matrix surrounding the IFs [23]. The keratins form a large family of proteins of acidic type Is (K31 to K40) and neutral-basic type IIs (K81 to K87), of about 400 to 500 amino acid residues.…”