The ultrastructure of Loxosceles silk ribbons

Silk ribbons spun by recluse (or brown) spiders (Loxosceles), orb-weaving spiders and silkworm fibers are all semicrystalline beta-sheet materials. Loxosceles silk differs, however, from these silks in its proposed hierarchical structural organization, although mechanical properties (e.g. tensile strength) are comparable. Indeed, spiders and silkworm fibers crystallinet nanodomains assemble with disordered protein spacers into cylindrical nanofibrils of 5-6 nm diameter, forming nanofibrillar bundles. Loxosceles ribbons show, however, anisotropic nanofibrils of 5-9 nm thickness and 20 nm width, forming a lauered structure. The ribbonsd tensile properties correspond to the average of tensile properties of the nanofibrils while modelling of spider silk suggests mesoscale chain confinement for optimized mechanical properties. Here, we here propose a systematic study of the hierarchical structural organization for single Loxosceles ribbons by scanning nanobeam SAXS/WAXS.