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Solid-state NMR determination of the secondary structure of Samia cynthia ricini silk

Nature volume 405, pages 1077–1079 (2000)Cite this article

Abstract

Silks are fibrous proteins that form heterogeneous, semi-crystalline solids. Silk proteins have a variety of physical properties reflecting their range of functions. Spider dragline silk, for example, has high tensile strength and elasticity1, whereas other silks2 are better suited to making housing, egg sacs or the capture spiral of spiders' webs. The differing physical properties arise from variation in the protein's primary and secondary structure, and their packing in the solid phase. The high mechanical performance of spider dragline silk, for example, is probably due to a β-sheet conformation of poly-alanine domains3, embedded as small crystallites within the fibre. Only limited structural information can be obtained from diffraction of silks3,4,5,6, so further characterization requires spectroscopic studies such as NMR7,8,9,10,11. However, the classical approach to NMR structure determination12 fails because the high molecular weight13, repetitive primary structure13 and structural heterogeneity of solid silk means that signals from individual amino-acid residues cannot be resolved. Here we adapt a recently developed solid-state NMR technique14,15 to determine torsion angle pairs (φ, Ψ) in the protein backbone, and we study the distribution of conformations in silk from the Eri silkworm, Samia cynthia ricini. Although the most probable conformation in native fibres is an anti-parallel β-sheet, film produced from liquid directly extracted from the silk glands appears to be primarily α-helical.

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Figure 1: The (φ,ψ)-dependence of DOQSY spectra in the two-spin approximation.
Figure 2: Experimental DOQSY spectra of silk from Samia cynthia ricini silkworms a, b, Spectra for fibre (a) and film (b ) samples.
Figure 3: Probability distribution functions for (φ,ψ) determined from the experimental spectra in Fig. 2 using Tikhonov regularization.

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Acknowledgements

This research was supported by the Swiss National Science Foundation, the European Science Foundation and the Bio-oriented Technology Research Advancement Institution, Japan (T.A.). We thank M. Ernst for experimental advice and R. Verel for discussion.

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Authors and Affiliations

  1. Laboratory for Physical Chemistry, ETH Zürich, Zürich, CH-8092, Switzerland

    J. D. van Beek, L. Beaulieu & B. H. Meier

  2. Laboratory of Physical Chemistry, University of Nijmegen, Toernooiveld, 6525 ED, Nijmegen, The Netherlands

    H. Schäfer

  3. Division of Biological Sciences Graduate School of Science, Hokkaido University, Sapporo, 060-0810, Japan

    M. Demura

  4. Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, 184-8588, Tokyo , Japan

    T. Asakura

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  1. J. D. van Beek
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Correspondence to B. H. Meier.

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van Beek, J., Beaulieu, L., Schäfer, H. et al. Solid-state NMR determination of the secondary structure of Samia cynthia ricini silk. Nature 405, 1077–1079 (2000). https://doi.org/10.1038/35016625

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