A detailed mapping of the readily accessible disulphide bonds in the cortex of wool fibres

Abstract

Trichocyte keratin intermediate filament proteins (keratins) and keratin associated proteins (KAPs) differ from their epithelial equivalents by having significantly more cysteine residues. Interactions between these cysteine residues within a mammalian fiber, and the putative regular organization of interactions are likely important for defining fiber mechanical properties, and thus biological functionality of hairs. Here we extend a previous study of cysteine accessibility under different levels of exposure to reducing compounds to detect a greater resolution of statistically nonrandom interactions between individual residues from keratins and KAPs. We found that most of the cysteines with this non-random accessibility in the KAPs were close to either the N-or C-terminal domains of these proteins. The most accessible nonrandom cysteines in keratins were present in the head or tail domains, indicating the likely function of cysteine residues in these regions is in readily forming intermolecular bonds with KAPs. Some of the less accessible non-random cysteines in keratins were discovered either close to or within the rod region in positions previously identified in human epithelial keratins as involved in crosslinking between the heterodimers of the tetramer. Our present study therefore provides a deeper understanding of the accessibility of disulfides in both keratins and KAPs and thus proves that there is some specificity to the disulfide bond interactions leading to these interand intra-molecular bonds stabilizing the fiber structure. Furthermore, these suggest potential sites of interaction between keratins and KAPs as well as keratin-keratin interactions in the trichocyte intermediate filament.

The Complexity of the Ovine and Caprine Keratin-Associated Protein Genes

“…In the wool follicles of sheep, the KAPs are produced soon after the synthesis of keratins during the development of fibres in the follicle, and they are thought to cross-link with the KIFs by forming disulphide bonds with cysteine residues in the head and tail domains of the keratins [ 1 ]. The nature of this cross-linking is not well understood, and while co-immunoprecipitation studies have demonstrated an interaction between the head domain of human keratin K86 and KAP2-1 [ 2 ], and Western blot studies have demonstrated an interaction between the head domain of K85 and KAP8-1 [ 2 ], a complete understanding of which K and KAP cysteine thiol groups form disulphide bridges (be they inter- or intra-chain) is not well known, although the bulk of the most readily accessible cysteines in the KAPs are reported to be found close to either the N- or C-terminal domains in these proteins [ 3 ]. The KAPs are thought to play a critical role in regulating the physico-mechanical properties of the fibre.…”

Redox proteomics analysis of hair shaft proteins upon hydrothermal and alkaline insult

“…demonstrated in their work on disulphide crosslinking in human keratins that a number of intermolecular crosslinks exist in the coil two regions between pairs of heterodimers. Further insights in the accessibility of cysteines in trichocyte keratins has been achieved by Plowman et al [14].…”

Perm-waved human hair: a thermorheologically complex shape memory composite

“…Finally, we are well aware that our decision to neglect certain factors may impose limitations on to the current analysis. First, the assumption of a homogeneous reductive/oxidative treatment is of only limited validity (70,71), namely, in view of the differences of the accessibility of the disulfide bonds (72). Second, the treatment will impart changes/damage to the IFs as well as the matrix in hair (73,74).…”