First Recombinant Expression, Purification, and Film Formation of a Single Solitary Bee Silk Protein from Osmia lignaria

Solitary bees account for most described bee species worldwide, with many spinning silk fibers to form protective cocoons during development; however, solitary bee silk proteins remain largely unexplored in recombinant systems and biomaterial fabrication. Here, we report the first recombinant expression and biomaterial formation from a solitary bee silk protein. Osmia lignaria silk fibroin 2 (OligF2) was expressed in Escherichia coli BL21(DE3) using an expression and purification scheme adapted from a recombinant hagfish intermediate filament (rHIF) workflow, yielding 0.34 g/L at ~70% purity. The purified OligF2 protein was cast into films at 0.75% and 1% (w/v). Fourier-transform infrared attenuated total reflectance (FTIR-ATR) analysis estimated higher β-sheet content in 0.75% films (50.3%) than in 1% films (42.3%). Mechanical testing yielded elastic moduli of 7.83 ± 2.73 MPa and 6.80 ± 1.89 MPa for the 0.75% and 1% films, respectively. These results establish the first recombinant production and biomaterial formation of a solitary bee silk protein, providing a foundation for exploring this class of recombinant proteins for the development of tunable biomaterials.