Elucidating silk structure using solid-state NMR

An overview of solid-state NMR structural studies on various silk forms and analogs conducted by the authors' research groups is presented. The well-studied silkworm and spider silks together with related silk peptides have a mixture of secondary structures including β-sheet, β-turn, helix and random coil that are difficult to analyze by X-ray diffraction and electron microscopy but conveniently investigated by solid-state NMR. Several newly developed solid-state NMR techniques and stable isotope labeling approaches of the silks were effectively used to characterize silk structure. The techniques discussed provide not only information on the secondary structure, but also on the hydrogen-bonding interactions present in the silks. Structural studies on other types of silk, silk peptide mimics and recombinant silk proteins are also discussed.