Transformation of Coiled α-Helices into Cross-β-Sheets Superstructure

Area of Science:

• Biomaterials Science
• Structural Biology
• Materials Chemistry

Background:

• Fibrous silks from Hymenoptera insects (bees, wasps, ants, hornets) naturally form a four-strand alpha-helical coiled coil superstructure.
• Understanding the structural properties of insect silks is crucial for developing novel biomaterials.

Purpose of the Study:

• To investigate the structural transformations in regenerated hornet silk (Vespa simillima xanthoptera) under tensile force.
• To determine if the characteristic four-strand coiled coil superstructure is maintained during structural transitions.

Main Methods:

• Wide- and small-angle X-ray scatterings (WAXS/SAXS).
• Polarized Fourier transform infrared spectroscopy (FTIR).
• Time-resolved synchrotron X-ray scattering for in situ monitoring during tensile deformation.

Main Results:

• Confirmed the formation of the four-strand alpha-helical coiled coil in natural and regenerated hornet silk films.
• Demonstrated that tensile force induces a structural transition from alpha-helices to a cross-beta-sheet superstructure in regenerated silk.
• Observed that the four-stranded tertiary superstructure remains intact during the alpha-helix to beta-sheet transition.
• Showed amorphous protein chains transform into oriented beta-sheet arrangements.

Conclusions:

• Regenerated hornet silk exhibits a reversible structural transition under tensile stress.
• The study elucidates the mechanical adaptability of insect silk structures, offering insights for biomimetic material design.