Structure of Bombyx mori Silk Fibroin before Spinning in Silkworm

摘要

The silk Ⅰ structure (the structure of Bombyx mori silk fibroin before spinning 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 1 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.