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Intermolecular Packing in B. mori Silk Fibroin: Multinuclear NMR Study of the Model Peptide (Ala-Gly)15 Defines a Heterogeneous Antiparallel Antipolar Mode of Assembly in the Silk II Form
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posted on 2015-01-13, 00:00 authored by Tetsuo Asakura, Takuya Ohata, Shunsuke Kametani, Keiko Okushita, Koji Yazawa, Yusuke Nishiyama, Katsuyuki Nishimura, Akihiro Aoki, Furitsu Suzuki, Hironori Kaji, Anne
S. Ulrich, Mike P. WilliamsonWe have previously suggested that
crystalline Bombyx mori silk in silk II form (the
silk structure after spinning) is not
a simple antiparallel β-sheet but is intrinsically heterogeneous.
Using the peptide (AG)15, we have obtained the first fully
assigned high resolution solid state 1H NMR spectrum. Distinct
heterogeneity was observed, in both 1H and 13C CP/MAS signals. Based on these results, a new model is proposed
that contains two different packing arrangements of antiparallel β-sheets.
The structures were energetically minimized by CASTEP calculation
and used to calculate the solid state 1H, 13C, and 15N NMR chemical shifts using the GIPAW method.
This new model was supported by good agreement between the calculated
and observed 1H, 13C, and 15N chemical
shifts and relative 1H–1H proximities
obtained from 2D 1H DQMAS experiments. We conclude that
the intermolecular packing of B. mori silk fibroin
has been finally resolved.