NMR Investigation about Heterogeneous Structure and Dynamics of Recombinant Spider Silk in the Dry and Hydrated States

Spider silks continue to attract researchers because of their excellent mechanical properties and supercontraction behavior. In this paper, the structure and dynamics of recombinant spider silk protein (RSP) were characterized using 13C CP/MAS, 13C DD/MAS, and 13C refocused-INEPT NMR spectroscopies in the dry and hydrated states. The fractions of several structures of RSP with helical, random coil, and β-sheet polyalanine sequences were determined from the CP/MAS NMR spectra in the dry state. The CP/MAS NMR spectra changed to very simple one with dominant β-sheet Ala peaks by hydration due to a significant loss in CP signals of the other mobile carbons. On the contrary, only sharp mobile peaks, and both mobile and immobile peaks could be observed in the refocused-INEPT and DD/MAS NMR spectra, respectively. The cis/trans proportion of the Gly–Pro bond was also determined. Our measurements provide new insight into understanding the supercontraction phenomenon of spider silks.