Structural Transition of Bombyx mori Liquid Silk Studied with Vibrational Circular Dichroism Spectroscopy

Abstract

7As another intermediate structure, an α-helix-rich crystalline Silk I structure was also observed by X-ray scattering 2015 © The Japan Society for Analytical Chemistry † To whom correspondence should be addressed. Agriculture and Technology, Koganei, Japan We investigated the structural transition from liquid silk to silk fibers with vibrational circular dichroism spectroscopy. Liquid silk showed a major right-handed optically active band at around 1650 cm -1 and a minor one at around 1680 cm -1 . The former disappeared over time, while the intensity in the latter increased. With the former wavenumber, liquid silk mainly adopted a random-coil structure. In contrast, the latter may reflect an intermediate structure in the transition. Furthermore, two right-handed bands at around 1630 and 1660 cm -1 appeared with the disappearance of the major band, and then the wavenumber of the former shifted to around 1620 cm -1 . The shift results from the decrease in the frequency of the CO stretching mode due to the stacking of the β-sheet that comprises fibers. The band at 1660 cm -1 may reflect another intermediate structure due to its strong correlation with that at 1620 cm -1 in terms of their temporal change in intensity.

Experimental Methods for Characterizing the Secondary Structure and Thermal Properties of Silk Proteins

“…These intermediate structures may provide more information on the temporal changes in silk as it transitions from the liquid state to solid fibers. [76] …”

Marine Structural Protein Stability Induced by Hofmeister Salt Annealing and Enzymatic Cross-Linking

“…Thus, we suggest that similarly to silk fibroin, when spun, suckerin-12 was able to transform from amorphous random coils to ordered structures like β-sheets and locked into place via rapid solvent removal . The susceptibility of suckerin-12 to shear induced organization also suggests that it could form organized secondary structures as observed in SRT where they provide additional film reinforcement …”

“…Furthermore, circular dichroism (CD) spectra exhibited a deep trough at 220 nm that suggests a heightened presence of random coils (dip at 205 nm) and helices (troughs at 203 and 223 nm). 29 CD of spin-cast suckerin-12 exhibits a peak at 190 nm and trough at 210 nm, which are characteristic of β-sheets, along with a slight shoulder at 205 nm that indicates the presence of random coils (Figure 3D). Therefore, we suggest that suckerin-12 undergoes shearinduced organization when spin-cast, which is characterized by a slight increase in β-sheet content (Figures 2 and 3).…”

“…31 The susceptibility of suckerin-12 to shear induced organization also suggests that it could form organized secondary structures as observed in SRT where they provide additional film reinforcement. 29 Spin-casting promotes the formation of ordered secondary structures stabilized by hydrogen bonds that also help prevent the breakdown of suckerin-12 films in water in contrast to immediate dissolution observed for drop cast suckerin after insertion in water.…”

Structural Discrimination between Aβ(1–40) and Aβ(1–42) Peptides in Films with Vibrational Circular Dichroism Spectroscopy

“…VCD spectroscopy, where one measures the circular dichroism activity in the molecular vibration region, is a powerful tool for the discrimination of slight differences between secondary structures of peptides and proteins in aqueous environments. [19][20][21] To form the aggregated states of Aβ(1-40) and Aβ(1-42), we prepared their hydrated films.…”