Unraveling the Molecular Origin of Prey-Wrapping Spider Silk's Unique Mechanical Properties and Assembly Process Using NMR

Prey wrapping spider silk's unique mechanical properties are investigated confirming the silk's high degree of extensibility and superior toughness compared to other types of spider silk. For the first time, the pre-spinning dope phase is studied in isotope-enriched intact aciniform (AC) silk glands using solution NMR that reveals a combination of alpha-helical domains linked by disordered random coil chains consistent with previously proposed "beads-on-a-string" models. The model is further refined through the AlphaFold2 protein structure prediction tool. Finally, extensive magic angle spinning (MAS) solid-state (SS) NMR data for isotopically-enriched fibers is used to refine the structural model for AC silk from two species, A. aurantia and A. argentata. The SSNMR data shows that the AC silk fibers are highly alpha-helical, coiled-coil in structure but, also exhibit significant beta-sheet components that can be traced back to the Gly-rich disordered linker regions in the pre-spinning dope phase that are converted to beta-sheet structures during fiber formation. This combination of mechanical and structural characterization enhances the understanding of AC silk's liquid-to-solid transition and structure-mechanics relationship. These prey wrap silk results and models will provide the basis for the design of biomimetic materials inspired by the AC spider silk system. Prey wrap silk exhibits a high extensibility and superior toughness compared to other types of spider silk. Solution NMR of intact silk glands and solid-state NMR of fibers are performed to elucidate the silk's unique liquid-to-solid transition. These results and models will provide the basis for the design of biomimetic materials inspired by the prey wrap spider silk system. image