Structure of Bombyx mori Silk Fibroin before Spinning in Silkworm

The silk I structure (the structure of Bombyx mori silk fibroin before ginning in the solid state) was determined with 13 C two-dimensional (2D) spin-diffusion solid-state NMR, rotational echo double resonance (REDOR) and quantitative use of 13 C CP/MAS NMR chemical shifts. We used 13 C - 13 C double labeled and 13 C - 15 N double labeled model peptides, (AlaGly)15 in silk I form for solid state NMR analyses. The structure was determined to a repeating type II β-turn. The solubility of B. mori silk fibroin in water was examined in the light of the presence of Tyr and Val residues in the repetitive domains of GAGAGYGAGAG and GAGVGYGAGAG sequences. The presence of amorphous domains, TGSSGFGPYVANGGYSGYEYAWSSESDFGT was also considered as the origin of the solubility of silk fibroin in water. The solution structure of silk fibroin in B. mori silkworm is also discussed with previous circular dichroism (CD), optical rotatory dispersion (ORD) and solution NMR data.