Structure of Spider Silk Studied with Solid-State NMR

Spider dragline silks exhibit remarkable mechanical properties, combining both high strength and toughness. These unique characteristics arise from the intricate structure of the silk, which requires atomic-level information to understand its origins. C-13 solid-state NMR provides this detailed structural insight into spider dragline silk. In this review, C-13 CP/MAS, C-13 DD/MAS and C-13 INEPT NMR spectroscopies are employed to reveal the structure of spider dragline silks together with C-13 conformation-dependent chemical shifts, 2D spin-diffusion NMR, rotational echo double resonance, dipolar-assisted rotational resonance, and angle-dependent NMR. The primary structure of major ampullate of spider dragline silk consists of repeated polyalanine and a glycine-rich regions. By analyzing the C-13 conformation-dependent chemical shifts and utilizing several solid-state NMR techniques, it has been proposed that the glycine-rich region primarily adopts a random coil conformation, including partially beta-sheet and beta-turn structures. This contradicts the previously suggested 3(1) helix conformation. On the other hand, the polyalanine region exhibits an antiparallel beta-sheet structure with staggered packing arrangements. Additionally, solid-state NMR has also revealed the structure of fragelliform spider silk. These findings contribute to the understanding of the remarkable properties of spider dragline silks and provide insights into its atomic-level architecture.