Chain-folded lamellar structure and dynamics of the crystalline fraction of Bombyx mori silk fibroin and of (Ala-Gly-Ser-Gly-Ala-Gly)n model peptides

Abstract

This is a repository copy of Chain-folded lamellar structure and dynamics of the crystalline fraction of Bombyx mori silk fibroin and of (Ala-Gly-Ser-Gly-Ala-Gly)n model peptides.

Structure of Silk I (Bombyx mori Silk Fibroin before Spinning) -Type II β-Turn, Not α-Helix-

“…This means a close relationship between the primary and secondary structures of silk fibroin before spinning. In addition, this type II β-turn structure is easy to form lamella structure (silk II) with distorted β-turn formed by repetitive folding using β-turns every eighth amino acid in an antipolar arrangement as reported previously by authors [ 16 , 19 ].…”

“…In order to determine the silk I structure, the authors used the peptide model (AG) 15 because the number of Ala, Gly, and Ser residues in the repeated AGSGAG sequences (crystalline region) are almost half of the total amino acid residues of silk fibroin [ 13 , 14 , 16 ]. An alternating copolypeptide (AG) n has been used for the structural model of silk fibroin by X-ray diffraction analysis [ 17 , 20 , 48 , 49 , 50 , 51 ].…”

“…The total number of AGSGAG sequence repeats is 433 (2598 amino acid residues). Because the total number of amino acid residues in the H chain is 5263, almost half is the AGSGAG sequence [ 16 ]. Motif (ii) is a relatively less repetitive sequence that contains hydrophobic and/or aromatic residues GAGAGY, GAGAGV, and GAGAGVGY.…”

“…Marsh et al [ 18 ] reported that silk II was antiparallel β-sheet structure based on the X-ray diffraction analysis of silk fiber. However, most recently, the authors proposed that silk II structure was a lamella structure using 13 C selectively labeled model peptides and solid-state NMR method [ 16 , 19 ]. Namely, two kinds of Ala residues in β-sheet structure, plus one distorted β-turn formed by repetitive folding using β-turns every eighth amino acid in an antipolar arrangement.…”

Structural investigations of polyurethane and silk‐polyurethane composite fiber studied by 13C solid‐state NMR spectroscopy

“…We have used these chemical shift data to monitor the conformation and also packing states of SF chains. [52][53][54][55][56] Namely, Ala carbon chemical shifts of SF give a good indicator of the conformation, that is, 19.6 and 21.7 ppm (Ala Cβ), 48.9 ppm (Ala Cα) and 172.0 ppm (Ala C O), respectively, for anti-parallel (AP) β-sheet structure, and 16.8 ppm (Ala Cβ), 50.0 ppm (Ala Cα) and 175.5 ppm (Ala C O), respectively, for random coil conformation. 52,53 Thus, the conformation of the regenerated SF fiber without PU1 prepared by the device wet spinning method is concluded to be mainly AP β-sheet structure (Figure 7(a)).…”