Chain-Folded Lamellar Stacking Structure of the Crystalline Fraction of Bombyx mori Silk Fibroin with Silk II Form Studied by 2D 13C–13C Homonuclear Correlation NMR Spectroscopy

• Published in: The journal of physical chemistry. B Vol. 128; no. 35; pp. 8459 - 8468
• Main Authors: Naito, Akira, Okushita, Keiko, Aoki, Akihiro, Asakura, Tetsuo
• Format: Journal Article
• Language: English
• Published: American Chemical Society 05.09.2024
• Subjects: amino acids; B: Biomaterials and Membranes; Bombyx mori; fibroins; nuclear magnetic resonance spectroscopy; physical chemistry; silk; standard deviation
• ISSN: 1520-6106; 1520-5207; 1520-5207
• DOI: 10.1021/acs.jpcb.4c03716

The structure of Bombyx mori silk fibroin (SF) is a subject of significant interest due to its remarkable physical properties; however, its atomic-level structure is still not conclusive. We previously proposed a lamellar stacking structure for the crystalline fraction (Cp) with β-turns occurring every eighth amino acid. In this study, we took the following steps: At first, a model of the chain-folded lamellar stacking structure in antipolar and antiparallel β-sheet layers was constructed. Then, dipolar-assisted rotational resonance solid-state NMR spectra were observed to determine the effective internuclear distance (r j,k eff) for the uniformly 13C-labeled Cp fraction sample. By comparing the experimentally obtained r j,k eff (obs) values with the calculated r j,k eff (calc) values from our structural model, a fairly good correlation between the observed and calculated values of the internuclear distances was obtained with a standard deviation of 0.37 Å. This supports the existence of the chain-folded lamellar stacking structure in the SF fiber. These findings contribute to our understanding of the atomic-level structure of SF and its exceptional properties.