Structural hysteresis in dragline spider silks induced by supercontraction: an X-ray fiber micro-diffraction study

Abstract

Interaction with water causes shrinkage and significant changes in the structure of spider dragline silks, which has been referred to as supercontraction in the literature. Preferred orientation or alignment of protein chains with respect to the fiber axis is extensively changed during this supercontraction process. Synchrotron x-ray micro-fiber diffraction experiments have been performed on Nephila clavipes and Argiope aurantia major and minor ampullate dragline spider fibers in the native dry, contracted (by immersion in water) and restretched (from contracted) states. Changes in the orientation of β-sheet nanocrystallites and the oriented component of the amorphous network have been determined from wide-angle x-ray diffraction patterns. While both the crystalline and amorphous components lose preferred orientation on wetting with water, the nano-crystallites regain their orientation on wet-restretching, whereas the oriented amorphous components only partially regain their orientation. Dragline major ampullate silks in both the species contract more than their minor ampullate silks.

Phase transitions as intermediate steps in the formation of molecularly engineered protein fibers

“…The orientation and size of β-sheet crystallites were quantitatively determined from azimuthal broadening (FWHM) of the 4.8 Å equatorial diffraction using the Hermans orientation function 39,43 and the Scherrer equation 41,44 . The value for the Hermans orientation parameter was maximally 0.76 for both CBM-eADF3-CBM and CBM-ADF3-CBM at 100% and increased to 0.82 and 0.81 at 150% strain indicating an increase of alignment along the tensile axis.…”

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

“…[21] Further work utilizing WAXS analysis revealed that the crystalline regions of dragline silk can regain orientation upon stretching after undergoing supercontraction, while the oriented-amorphous regions have limited ability to recover their orientation. [87] This work suggests that not only crystalline content but also orientation may be a key determinant of fiber mechanical properties, and highlights the utility of WAXS analysis in studying these parameters.…”

Influence of Sodium Bisulfite and Lithium Bromide Solutions on the Shape Fixation of Camel Guard Hairs in Slenderization Process

“…Soaking in water for a certain period shows the longitudinal contraction of guard hair fiber after being soaked in three solutions. Unlike the supercontraction of spider silk encountered with water [16,17], the contraction of camel hairs in longitudinal direction is noted to be negligible, which may be due to the large amount of residue chemical cross-linkage of macromolecules in diametral direction. Figure 3(a) shows the smoothed XRD characteristic traces of guard hairs under four statuses.…”