Vibrational 13C-cross-polarization/magic angle spinning NMR spectroscopic and thermal characterization of poly(alanine-glycine) as model for silk I Bombyx mori fibroin.
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 13C-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 beta-turn type II conformation, thus confirming the results of those who propose a repeated beta-turn type II structure for silk I. The analysis of the Raman spectra in the nuNH 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.
Monti
Patrizia
P
Dipartimento di Biochimica G. Moruzzi, Sezione di Chimica e Propedeutica Biochimica, Centro di Studi Sulla Spettroscopia Raman, Università di Bologna, Via Belmeloro 8/2, 40126 Bologna, Italy. patmonti@ciam.unibo.it
Taddei
Paola
P
Freddi
Giuliano
G
Ohgo
Kosuke
K
Asakura
Tetsuo
T
D000818:Animals; D012831:Bombyx / Q000378:metabolism*; D002918:Chymotrypsin / Q000737:chemistry; D005349:Fibroins / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D013696:Temperature
D010455:Peptides; C019529:polyalanine; D005349:Fibroins; D002918:Chymotrypsin; D005998:Glycine