Abstract
Solid state NMR has been successfully used for structural determination of silk fibroins whose single crystals are difficult to prepare. The structure of the crystalline region of silk fibroin from the domesticated silkworm, Bombyx mori, before spinning (Silk I) in the solid state was first determined. For the purpose, several stable-isotope labeled model peptides, (AG)15, were synthesized. Then, several solid state NMR methods; quantitative use of the conformation-dependent 13C CP/MAS chemical shifts, 13C two-dimensional solid-state spin-diffusion NMR and rotational echo double resonance techniques, were used for the structural analysis. The heterogeneous structure of the same silk fibroin after spinning (Silk II) has been also determined with solid state NMR. The structural change from Silk I to Silk II was reproduced using molecular dynamics simulation by considering several external forces applied to the silk fibroin in the silkworm. The structural analyses of Samia cynthia ricini silk fibroin and spider silks have also been reviewed. Finally, designs of new silk-like materials based on these structural information and their productions with Escherichia coli were described.
