Spider silk fibre extrusion: combined wide- and small-angle X-ray microdiffraction experiments

Area of Science:

• Biomaterials Science
• Materials Science
• Structural Biology

Background:

• Spider silk's unique mechanical properties are attributed to its complex molecular structure.
• Understanding silk formation in situ provides insights into structure-property relationships.

Purpose of the Study:

• To investigate the in situ structural characteristics of major and minor ampullate silks during forced silking.
• To correlate structural features with the mechanical properties of spider dragline silk.

Main Methods:

• In situ X-ray diffraction (WAXS and SAXS) during forced silking of Nephila senegalensis and Euprostenops spp. spiders.
• Analysis of scattering patterns to determine crystallite structure and microfibril morphology.

Main Results:

• Beta-sheet poly(alanine) crystallites are present at the spigot exit in major ampullate silk.
• Microfibrils with an 8 nm axial repeat are observed in major ampullate silks, but not in minor ampullate silk.
• A microfibrillar model explains observed X-ray diffraction patterns, suggesting water is extruded during natural dragline production.

Conclusions:

• Spider silk's hierarchical structure, including crystallites and microfibrils, forms during extrusion.
• Water extrusion, facilitated by the spider's tarsal claws, is crucial for optimizing silk mechanical properties.
• Differences in structure between major and minor ampullate silks are linked to poly(alanine) content.