Structural analysis of Bombyx mori silk fibroin peptides with formic acid treatment using high-resolution solid-state 13C NMR spectroscopy.

Bombyx mori silk fibroin fiber is a fibrous protein produced by the silkworm at room temperature and from an aqueous solution whose primary structure is highly repetitive. In this study we analyzed the structural characteristics of native peptides, derived from B. mori silk fibroin, with formic acid treatment using high-resolution solid-state 13C NMR. We establish that the Ser residue bearing a short polar side chain has the ability to stabilize the conformation formed in the model peptides due to its ability to form intermolecular hydrogen bonds involving its hydroxyl group as a donor and the carbonyl groups of other residues as acceptors. On the other hand, insertion of Tyr residue in the basic (AG)n and (AGSGAG)n sequence motifs usually exhibited disruptive effects on the preferred conformations. Moreover, the environmental effect was investigated by mixing the native Cp fraction with the model peptides, showing that there is no significant structural difference on the Ser-containing peptides, while st...