Protein disulphide isomerase-assisted functionalization of keratin-based matrices

In living systems, protein disulphide isomerase (PDI, EC 5.3.4.1) regulates the formation of new disulphide bonds in proteins (oxidase activity) and catalyzes the rearrangement of non-native disulphide bonds (isomerase activity), leading proteins towards their native configuration. In this study, PDI was used to attach cysteine-containing compounds (CCCs) onto hair, to enhance compound migration within hair fibre and to trigger protein release. A fluorescent (5(6)-TAMRA)-labelled keratin peptide was incorporated into hair by using PDI. Similarly, PDI promoted the grafting of a cysteine-functionalized dye onto wool, as suggested by matrix-assisted laser desorption and ionization time-of-flight results. These reactions were thought to involve oxidation of disulphide bonds between CCCs and wool or hair cysteine residues, catalyzed by the oxidized PDI active site. On the other hand, PDI was demonstrated to enhance the migration of a disulphide bond-functionalized dye within the keratin matrix and trigger the release of RNase A from wool fibres' surface. These observations may indicate that an isomerisation reaction occurred, catalyzed by the reduced PDI active site, to achieve the thiol-disulphide exchange, i.e. the rearrangement of disulphide bonds between CCCs and keratin. The present communication aims to highlight promising biotechnological applications of PDI, derived from its almost unique properties within the isomerase family.