Molecular disorder and structure of spider dragline silk investigated by two-dimensional solid-state NMR spectroscopy

We have studied the molecular disorder in (C-13)Ala- and (C-13)Gly-labeled dragline silk from Nephila edulis through the distributions of isotropic chemical shifts in one- and two-dimensional C-13-C-13 NMR spectra obtained under MAS. The alanine residues were found to be present in two distinct major structural environments, in agreement with previous studies, where beta-sheets and 3(1)-helices were found. The distributions in chemical shift within each residue were found to be uncorrelated, even between spins in the same amino acid residue, and were of similar widths for both the crystalline and noncrystalline parts. Upon long-term mechanical stretching of the silk, the NMR spectra showed no significant changes in conformation nor changes in the degree of disorder but did show increasing structural damage to the silk threads.