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Issue 78, 2014
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Structural characterization of nanofiber silk produced by embiopterans (webspinners)

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Abstract

Embiopterans produce silken galleries and sheets using exceptionally fine silk fibers in which they live and breed. In this study, we use electron microscopy (EM), Fourier-transform infrared (FT-IR) spectroscopy, wide angle X-ray diffraction (WAXD) and solid-state nuclear magnetic resonance (ssNMR) techniques to elucidate the molecular level protein structure of webspinner (embiid) silks. Silks from two species Antipaluria urichi and Aposthonia ceylonica are studied in this work. Electron microscopy images show that the fibers are about 90–100 nm in diameter, making webspinner silks among the finest of all known animal silks. Structural studies reveal that the silk protein core is dominated by β-sheet structures, and that the protein core is coated with a hydrophobic alkane-rich surface coating. FTIR spectra of native embiid silk shows characteristic alkane CH2 stretchings near 2800–2900 cm−1, which decrease approximately 50% after washing the silk with 2 : 1 CHCl3 : MeOH. Furthermore, 13C ssNMR data shows a significant CH2 resonance that is strongly affected by the presence of water, supporting the idea that the silk fibers are coated with a hydrocarbon-rich layer. Such a layer is likely used to protect the colonies from rain. FTIR data also suggests that embiid silks are dominated by β-sheet secondary structures similar to spider and silkworm silk fibers. NMR data confirms the presence of β-sheet nanostructures dominated by serine-rich repetitive regions. A deconvolution of the serine Cβ NMR resonance reveals that approximately 70% of all seryl residues exist in a β-sheet structure. This is consistent with WAXD results that suggest webspinner silks are 70% crystalline, which is the highest crystalline fraction reported for any animal silks. The work presented here provides a molecular level structural picture of silk fibers produced by webspinners.

Graphical abstract: Structural characterization of nanofiber silk produced by embiopterans (webspinners)

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Supplementary files

Article information


Submitted
24 Jul 2014
Accepted
26 Aug 2014
First published
29 Aug 2014

This article is Open Access

RSC Adv., 2014,4, 41301-41313
Article type
Paper
Author version available

Structural characterization of nanofiber silk produced by embiopterans (webspinners)

J. B. Addison, T. M. Osborn Popp, W. S. Weber, J. S. Edgerly, G. P. Holland and J. L. Yarger, RSC Adv., 2014, 4, 41301
DOI: 10.1039/C4RA07567F

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