Key locations of oxidative damage in human hair keratins after heat and ultraviolet light exposure.

Objective: This study investigated the locations of amino acid modifications within two major human hair keratins (Type I K31 and Type II K85) with probable implications for protein and hair structural component integrity. The particular focus was on cysteine modifications that disrupt intra-protein and inter-protein disulphide bonds.

Methods: Human hair was exposed to accelerated, sequential heat or UV treatments, simulating effects resulting from the use of heated styling tools and environmental exposure over a time frame approximating one year. The proteins were extracted and detected using LC-MS/MS and identified by matching to protein databases. The sites of disulphide-disrupting amino acid residue modifications were mapped to known structural domains of the keratins.

Results: Disulphide bond-disrupting cysteine modifications (formation of cysteic acid and dehydroalanine) arose in K31 and K85 after treatments with UV and with heat. These modifications were mapped to both the relatively amorphous (head) regions of the keratins, which bind with keratin-associated proteins, and the more structured coil regions, which bind to other keratins.

Conclusion: These data provide confirmation that heat- and UV-induced disulphide bond disruption resulted in post-translational modifications that are crucial for secondary structural interactions, the loss of which has the potential to affect the loss of structural integrity observed in human hair after the use of repeated styling processes or prolonged weathering from sunlight exposure.