Ionic liquid-assisted extraction of wool keratin proteins as an aid to MS identification

Investigations into the use of the ionic liquid 1-butyl-3-methylimidazolium chloride [BMIM]⁺[Cl]^- to extend the mapping of the wool proteome have established that it is complementary to the use of commonly used chaotropic agents such as urea. Extraction of proteins from wool is challenging with only 50-60% extraction possible by traditional methods that utilise chaotropes in the presence of a reducing agent. Incubation of wool at high temperatures in the presence of [BMIM]⁺[Cl]^- resulted in large scale disruption of the fibre into cells and sub-cellular fragments. The combination of the proteins identified from the ionic liquid treated wool which was subsequently extracted with urea/thiourea and those identified by urea/thiourea extraction alone resulted in the identification of a larger set of proteins from the wool fibre than would have been found by either method alone. Wool proteins, in particular some trichocyte keratins, were uniquely identified with the ionic liquid/(urea/thiourea) combination, while others such as some of the keratin associated proteins were unique to urea/thiourea alone. We conclude that the ionic liquid/(urea/thiourea) method provides complementary coverage of the wool proteome when run alongside the traditional urea/thiourea method.