Vibrational infrared conformational studies of model peptides representing the semicrystalline domains of Bombyx mori silk fibroin

Abstract

The structural organization of Bombyx mori silk fibroin was investigated by infrared (IR) spectroscopy. To this aim, (AG)15 and other model peptides of varying chain length, containing tyrosine (Y), valine (V), and serine (S) in the basic (AG)n sequence were synthesized by the solid phase method and their spectroscopic properties were determined. Both the position and the relative content of Y, V, and S residues in the (AG)n model system appeared critical in determining the preferred conformation, i.e., silk I, silk II, and unordered structures. Curve fitting analysis in the amide I range showed that the model peptides with prevailing silk II structure displayed different beta-sheet content, which was dependent on the degree of interruption of the (AG)n sequence. In this regard, the bands at about 1000 and 980 cm(-1), specifically assigned to the AG sequence of the B. mori silk fibroin chain, were identified as marker of the degree of interruption of the (AG)n sequence.A stable silk I structure was observed only when the Y residue was located near the chain terminus, while a silk I --> silk II conformational transition occurred when it was positioned in the central region of the peptide. Analysis of the second-derivative spectra in the amide I range allowed us to identify a band at 1639 cm(-1) (4 --> 1 hydrogen-bonded type II beta-turns), which is characteristic of the silk I conformation.

An investigation into silk fibroin conformation in composite materials intended for drug delivery

“…1). These features were due to a prevalent random coil conformation (Taddei and Monti, 2005). The spectrum of the cast SF was very close to that of the spray-dried SF, even if the bands assigned to amide I (1635 cm −1 ), and amide III (1231 cm −1 ) slightly shifted towards higher wavenumbers, suggesting the formation of a less disordered structure in the cast SF.…”

Effect of UV-light on the uniaxial tensile properties and structure of uncoated and TiO2 coated Bombyx mori silk fibers

“…Here, the band at around 700 cm À1 which was observed at 690 cm À1 in the spectra of uncoated and TiO 2 coated silk filaments is assigned to Amide V band [30,32]. The weak bands at 976 and 1000 cm À1 being not separated clearly but estimated under the peak at 1068 cm À1 corresponding to C a -C stretching vibration of peptides in b-sheet conformation [33][34][35] are assigned respectively to CH 3 rock and C a -C b stretch, and CH 3 rock in AlaGly repeating pattern in b-sheet conformation [33,36]. Amide III mode for random-coil conformation and b-sheet conformation were observed at 1235 and 1256 cm À1 [33,34,37].…”

“…Amie I band which is the C@O stretching vibration with minor contributions from the outof-phase C-N stretching vibration and the C-N-H in plane bending was observed at 1616 cm À1 and 1645 cm À1 for b-sheet conformation in b-sheet crystalline structures [31,33,34] and for unordered conformation [34,35,41], respectively. In the Amide A spectral region (3600-2800 cm À1 ), two peaks at 2853 and 2923 cm À1 are due to C-H stretching in the peptide chains and assigned to the symmetrical and antisymmetrical C-H stretching of CH 2 [30,31,33], respectively.…”

Autoclaving as a chemical-free process to stabilize recombinant silk-elastinlike protein polymer nanofibers

“…The secondary-derivative method was used to identify individual characteristic bands of the FSD amide I bands. 10 Areas under individual bands normalized by the total area of the amide I band represent the percentage contents of secondary structures of the nanofibers. 9 Specifically, the band at 1616 cm À1 was assigned to aggregated strands, while bands at 1624, 1635, 1675, and 1695 cm À1 were assigned to b-sheet and sheetlike structure.…”

“…9 Specifically, the band at 1616 cm À1 was assigned to aggregated strands, while bands at 1624, 1635, 1675, and 1695 cm À1 were assigned to b-sheet and sheetlike structure. 10 Bands at 1662, 1669, and 1684 cm À1 were assigned to b-turns. Bands at 1646 and 1653 cm À1 were assigned to unordered structures and a-helix, respectively.…”