Structure and Structural Changes of the Silk Fibroin from Samia cynthia ricini Using Nuclear Magnetic Resonance Spectroscopy

✍ Scribed by Tetsuo Asakura; Yasumoto Nakazawa

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 457 KB
• Volume: 4
• Category: Article
• ISSN: 1616-5187
• DOI: 10.1002/mabi.200300098

✦ Synopsis

Abstract

Summary: The structure of silk fibroin from a wild silkworm, S. c. ricini, the amino acid sequence of which consists of repeated poly‐Ala and Gly‐rich regions, was examined by using solution and solid‐state NMR methods. The structural transition of the silk fibroin in aqueous solution was monitored by using ^13^C solution NMR spectroscopy as a function of temperature. The fast exchange with respect to the chemical shift between the helix and coil conformations was observed in the poly‐Ala region and the slow conformational change from α‐helix to random coil was observed for the Gly residue adjacent to the N‐terminal Ala residue of the poly‐Ala region. The torsion angles of several Ala and Gly residues in the model peptide, GGAGGGYGGDGG(A)~12~GGA‐GDGYGAG, were determined by the conformation‐dependent ^13^C chemical shifts, rotational echo double resonance (REDOR) and 2D spin‐diffusion NMR methods. The solid‐state NMR analysis leads to the precise silk structure before spinning, where the poly‐Ala sequence takes a typical α‐helix pattern with a tightly winded helical structure at both terminal regions of the poly‐Ala sequence. This is expected to stabilize the α‐helical structure of the poly‐Ala region in S. c. ricini silk fibroin from the silkworm.

The proposed helical structure of poly(L‐alanine) region of S. c. ricini silk fibroin before spinning.

imageThe proposed helical structure of poly(L‐alanine) region of S. c. ricini silk fibroin before spinning.