Vibrational 13C-cross-polarization/magic angle spinning NMR spectroscopic and thermal characterization of poly(alanine-glycine) as model for silk I Bombyx mori fibroin
✍ Scribed by Patrizia Monti; Paola Taddei; Giuliano Freddi; Kosuke Ohgo; Tetsuo Asakura
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 2003
- Tongue
- English
- Weight
- 285 KB
- Volume
- 72
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Abstract
This study focuses on the conformational characterization of poly(alanine‐glycine) II (pAG II) as a model for a Bombyx mori fibroin silk I structure. Raman, IR, and ^13^C‐cross‐polarization/magic angle spinning NMR spectra of pAG II are discussed in comparison with those of the crystalline fraction of B. mori silk fibroin (chymotryptic precipitate, Cp) with a silk I (silk I‐Cp) structure. The spectral data give evidence that silk I‐Cp and the synthetic copolypeptide pAG II have similar conformations. Moreover, the spectral findings reveal that silk I‐Cp is more crystalline than pAG II; consequently, the latter contains a larger amount of the random coil conformation. Differential scanning calorimetry measurements confirm this result. N‐Deuteration experiments on pAG II allow us to attribute the Raman component at 1320 cm^−1^ to the amide III mode of a β‐turn type II conformation, thus confirming the results of those who propose a repeated β‐turn type II structure for silk I. The analysis of the Raman spectra in the νNH region confirms that the silk I structure is characterized by the presence of different types of H‐bonding arrangements, in agreement with the above model. © 2003 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 72: 329–338, 2003