Structural analyses of silk fibroins based on the structures of oligoalanine, and periodic oligopeptides of L‐alanine and glycine using x‐ray diffraction and ¹³C solid‐state NMR methods

Abstract

The structures of (A)12, (AAAG)7, (AAG)10, (AG)15, and (AGG)10 were determined using x‐ray diffraction and 13C sold‐state NMR methods after different solvent treatments to obtain knowledge about the structural changes of silk fibroins (SFs) from Samia cynthia ricini (S.c.ricini) and Bombyx mori (B. mori). Three solvent treatments were performed: precipitation from dialysis of LiSCN (LiSCN/Dialysis) or LiBr (LiBr/Dialysis) aqueous solutions, and drying from formic acid (FA) or trifluoroacetic acid (TFA) solutions. (AAAG)7 and (AAG)10 as models of S.c.ricini SF, formed antiparallel β‐sheet structure with staggered packing configuration and did not change after LiSCN/Dialysis or LiBr/Dialysis and FA treatments. (AGG)10 formed 31 helix structure and did not change with these solvent treatments either. On the other hand, (AG)15 as model of B. mori SF formed Silk I (type II β‐turn) structure after LiBr/Dialysis treatment and Silk II (lamellar packing) structure after FA treatment. Especially, B. mori SF seems useful for biomaterials.