Heterogeneous structure of silk fibers from Bombyx mori resolved by 13C solid-state NMR spectroscopy.
The molecular conformation of silk fibrion is characterized by solid-state 13C NMR before spinning (silk I structure) and after spinning (silk II structure). We compare native silk fibers with the quasi-crystalline Cp-fraction and a synthetic model peptide (Ala-Gly)15, both of which can be converted either into silk I by dialysis from 9 M LiBr or into silk II by treatment with formic acid. Our results demonstrate that silk II fibers are intrinsically heterogeneous, consisting of beta-sheets, distorted beta-turns, and distorted beta-sheets. This higher-order heterogeneity is revealed by the 13C-NMR Cbeta-peak of Ala, indicating that the Ala side chains are stacked partially in parallel and partially face-to-face, at a ratio of 1:2.
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan. asakura@cc.tuat.ac.jp
Tetsuo
T
Asakura
Juming
J
Yao
Tsutomu
T
Yamane
Kosuke
K
Umemura
Anne S
AS
Ulrich
D000818:Animals; D012831:Bombyx / Q000378:metabolism*; D002247:Carbon Isotopes; D019476:Insect Proteins / Q000737:chemistry* / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011487:Protein Conformation; D047011:Silk
D002247:Carbon Isotopes; D019476:Insect Proteins; D047011:Silk