The next generation of protein super-fibres: robust recombinant production and recovery of hagfish intermediate filament proteins with fibre spinning and mechanical-structural characterizations

Native hagfish intermediate filament proteins have impressive mechanical properties. However, using these native fibres for any application is impractical, necessitating their recombinant production. In the only literature report on the proteins (denoted alpha and (sic)), heterologous expression levels, using E. coli, were low and no attempts were made to optimize expression, explore wet-spinning, or spin the two proteins individually into fibres. Reported here is the high production (similar to 8 g l(-1) of dry protein) of the hagfish intermediate filament proteins, with yields orders of magnitude higher (325-10003) than previous reports. The proteins were spun into fibres individually and in their native-like 1:1 ratio. For all fibres, the hallmark alpha-helix to beta-sheet conversion occurred after draw-processing. The native-like 1:1 ratio fibres achieved the highest average tensile strength in this study at nearly 200 MPa with an elastic modulus of 5.7 GPa, representing the highest tensile strength reported for these proteins without chemical cross-linking. Interestingly, the recombinant alpha protein achieved nearly the same mechanical properties when spun as a homopolymeric fibre. These results suggest that varying the two protein ratios beyond the natural 1:1 ratio will allow a high degree of tunability. With robust heterologous expression and purification established, optimizing fibre spinning will be accelerated compared to difficult to produce proteins such as spider silks.