Development of silk-like materials based on Bombyx mori and Nephila clavipes dragline silk fibroins

In order to develop new silk-like materials in the form of fiber and non-woven nano-fiber, this study synthesized a new silk-like protein by selecting the sequence from the crystalline region of Bombyx mori silk fibroin, (GAGSGA)6, to imitate the processing condition of the silk fibroin with the combination of the sequence YGGLGSQGAGRG, the hydrophilic motif of spider dragline silk which was considered as the origin of supercontraction of spider dragline silk (Yang Z, et al. J Am Chem Soc 2000;122: 9019-25). The CD pattern of the silk-like protein in hexafluoroacetone (HFA) indicates that it takes helical structure. The solid-state structures of the silk-like protein before and after methanol treatment were determined to be random coil and Silk II structure (mainly β-sheet structure), respectively, using 13C CP/MAS NMR. The 13C CP/MAS NMR spectra of the protein after methanol treatment in hydrated state showed that the random coil peaks from Ala Cβ and Ser Cβ carbons become sharper compared with the corresponding peaks in the dry state. The 2D-WISE spectra in the hydrated state also showed increase of the narrow components for these carbons. Thus, water molecules are relatively easy to access at the random coil regions of the protein. The fiber formation of the silk-like protein was possible with wet-spinning or electrospinning methods using HFA as dope solvent and methanol as coagulation solvent.