Protein secondary structure in spider silk nanofibrils

Abstract

Nanofibrils play a pivotal role in spider silk and are responsible for many of the impressive properties of this unique natural material. However, little is known about the internal structure of these protein fibrils. We carry out polarized Raman and polarized Fourier-transform infrared spectroscopies on native spider silk nanofibrils and determine the concentrations of six distinct protein secondary structures, including β-sheets, and two types of helical structures, for which we also determine orientation distributions. Our advancements in peak assignments are in full agreement with the published silk vibrational spectroscopy literature. We further corroborate our findings with X-ray diffraction and magic-angle spinning nuclear magnetic resonance experiments. Based on the latter and on polypeptide Raman spectra, we assess the role of key amino acids in different secondary structures. For the recluse spider we develop a highly detailed structural model, featuring seven levels of structural hierarchy. The approaches we develop are directly applicable to other proteinaceous materials.

Nanoscale imaging of major and minor ampullate silk from the orb-web spider Nephila Madagascariensis

“…Fibril diameters were found to vary between 145 nm ± 18 and 116 nm ± 12 depending on the fibre and fibre type, suggesting that the fibres exhibit considerable natural diversity. This is supported by recent results using AFM 17 and SEM 43 . Furthermore, studies in different spider species also show considerable variations 37 .…”

“…However, for those measurements’ samples were also cryogenically frozen before imaging, fostering a misinterpretation of cavities as 'fibrils' 10 . Fibral widths of down to 50 nm have been reported for Loxosceles laeta silk 17 . In light microscopy studies of silk structure the samples were submerged in urea and studied under super contraction conditions, which supports unwanted delamination processes 18 – 20 .…”

Recombinant Spider Silk Fiber with High Dimensional Stability in Water and Its NMR Characterization

“…A variety of techniques, such as X-ray diffraction, Fourier transform infrared/Raman spectroscopy, transmission electron microscopy, and so on, were used to elucidate the structure of spider dragline silk, from its secondary structure, to its molecular arrangement, to its hierarchical structure [ 1 , 2 , 3 , 4 , 5 , 6 ]. However, the most detailed picture of the structure and dynamics of spider silk at the molecular level was obtained from NMR spectroscopy.…”

“…Spider dragline silks have attracted much attention as a potential source of next-generation biomaterials and textiles because of their outstanding mechanical properties and biocompatibility [ 1 , 2 , 3 , 4 , 5 , 6 ]. The spider silks have a unique property, supercontraction, which occurs in the hydration process, i.e., interaction with water causes the spider dragline silk fiber to contract by up to 50% in length and to transition from glassy to rubbery phases [ 7 , 8 , 9 , 10 , 11 ].…”

Genetically Engineered Protein-Based Bioadhesives with Programmable Material Properties

“…The baselined amide I band was deconvoluted into 11 distinct Lorentzian peaks centered at 1618.5, 1624.5, 1632.5, and 1700 cm –1 for the β-sheet, 1610, 1642, and 1651 cm –1 for random coil, 1659 cm –1 for α-helix, and 1666.5, 1678, and 1691 cm –1 for the β-turn. Peak centers were assigned based on those used in previous studies. ,,, Peak areas were integrated, and area percentages were calculated as the individual peak areas over the sum of all peak areas.…”