Protein secondary structure of Green Lynx spider dragline silk investigated by solid-state NMR and X-ray diffraction

In this study, the secondary structure of the major ampullate silk from Peucetia viridans (Green Lynx) spiders is characterized by X-ray diffraction and solid-state NMR spectroscopy. From X-ray diffraction measurement, beta-sheet nanocrystallites were observed and found to be highly oriented along the fiber axis, with an orientational order, f(c) approximate to 10.98. The size of the nanocrystallites was determined to be on average 2.5 nm x 3.3 nm x 3.8nm. Besides a prominent nanocrystalline region, a partially oriented amorphous region was also observed with an f(a) approximate to 0.89. Two-dimensional C-13-C-13 through-space and through-bond solid-state NMR experiments were employed to elucidate structure details of P. viridans silk proteins. It reveals that beta-sheet nanocrystallites constitutes 40.0 +/- 1.2% of the protein and are dominated by alanine-rich repetitive motifs. Furthermore, based upon the NMR data, 18 +/- 1% of alanine, 60 +/- 12% glycine and 54 +/- 2% serine are incorporated into helical conformations. (C) 2015 Elsevier B.V. All rights reserved.