Glycerin-Induced Conformational Changes in Bombyx mori Silk Fibroin Film Monitored by (13)C CP/MAS NMR and ¹H DQMAS NMR.
In order to improve the stiff and brittle characteristics of pure Bombyx mori (B. mori) silk fibroin (SF) film in the dry state, glycerin (Glyc) has been used as a plasticizer. However, there have been very limited studies on the structural characterization of the Glyc-blended SF film. In this study, (13)C Cross Polarization/Magic Angle Spinning nuclear magnetic resonance (CP/MAS NMR) was used to monitor the conformational changes in the films by changing the Glyc concentration. The presence of only 5 wt % Glyc in the film induced a significant conformational change in SF where Silk I* (repeated type II β-turn and no α-helix) newly appeared. Upon further increase in Glyc concentration, the percentage of Silk I* increased linearly up to 9 wt % Glyc and then tended to be almost constant (30%). This value (30%) was the same as the fraction of Ala residue within the Silk I* form out of all Ala residues of SF present in B. mori mature silkworm. The ¹H DQMAS NMR spectra of Glyc-blended SF films confirmed the appearance of Silk I* in the Glyc-blended SF film. A structural model of Glyc-SF complex including the Silk I* form was proposed with the guidance of the Molecular Dynamics (MD) simulation using ¹H-¹H distance constraints obtained from the ¹H Double-Quantum Magic Angle Spinning (DQMAS) NMR spectra.
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8488, Japan. asakura@cc.tuat.ac.jp.
Tetsuo
T
Asakura
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8488, Japan. Kah-vetophs@agate.plala.or.jp.
Masanori
M
Endo
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8488, Japan. misaki.h.0822@gmail.com.
Misaki
M
Hirayama
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8488, Japan. h-arai@elleair-product.com.
Hiroki
H
Arai
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8488, Japan. a_aoki@cc.tuat.ac.jp.
Akihiro
A
Aoki
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8488, Japan. fv0177@go.tuat.ac.jp.
Yugo
Y
Tasei
D000818:Animals; D012831:Bombyx / Q000737:chemistry / Q000378:metabolism*; D066241:Carbon-13 Magnetic Resonance Spectroscopy; D004305:Dose-Response Relationship, Drug; D005349:Fibroins / Q000737:chemistry*; D005990:Glycerol / Q000737:chemistry / Q000494:pharmacology*; D019476:Insect Proteins / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D017433:Protein Structure, Secondary; D066244:Proton Magnetic Resonance Spectroscopy
D019476:Insect Proteins; D005349:Fibroins; D005990:Glycerol
Bombyx mori; glycerin; silk fibroin; solid state NMR