The susceptibility of disulfide bonds to modification in keratin fibres undergoing tensile stress.
Biophys J 2022;
121:2168-2179. [PMID:
35477858 DOI:
10.1016/j.bpj.2022.04.029]
[Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 03/23/2022] [Accepted: 04/25/2022] [Indexed: 11/21/2022] Open
Abstract
Cysteine residues perform a dual role in mammalian hairs. The majority help stabilise the overall assembly of keratins and their associated proteins, but a proportion of inter-molecular disulfide bonds are assumed to be associated with hair mechanical flexibility. Hair cortical microstructure is hierarchical, with a complex macro-molecular organisation resulting in arrays of intermediate filaments at a scale of micrometres. Intermolecular disulfide bonds occur within filaments and between them and the surrounding matrix. Wool fibres provide a good model for studying various contributions of differently situated disulfide bonds to fibre mechanics. Within this context it is not known if all intermolecular disulfide bonds contribute equally, and, if not, then do the disproportionally involved cysteine residues occur at common locations on proteins. In this study, fibres from Romney sheep were subjected to stretching or to breaking point under wet or dry conditions to detect, through labelling, disulfide bonds that were broken more often than randomly. We found that some cysteines were labelled more often than randomly and that these vary with fibre water content (water disrupts protein-protein hydrogen bonds). Many of the identified cysteine residues were located close to the terminal ends of keratins (head or tail domains) and keratin-associated proteins (KAPs). Some cysteines in the head and tail domains of type II keratin K85 were labelled in all experimental conditions. When inter-protein hydrogen bonds were disrupted under wet conditions, disulfide labelling occurred in the head domains of type II keratins, likely affecting keratin-KAP interactions, and tail domains of the type I keratins, likely affecting keratin-keratin interactions. In contrast, in dry fibres (containing more protein-protein hydrogen bonding) disulfide labelling was also observed in the central domains of affected keratins. This central "rod" region is associated with keratin-keratin interactions between anti-parallel heterodimers in the tetramer of the intermediate filament.
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