Spiders' silky secrets: Unravelled by NMR

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  • Published: Nov 15, 2019
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Spiders' silky secrets: Unravelled by NMR

Silky, silky

Spider's web photo by David Bradley High-resolution nuclear magnetic resonance (NMR) spectroscopy and photoinduced electron transfer fluorescence correlation spectroscopy (PET-FCS) have been used to show how protein dynamics in spider silk is mediated by the amino acid methionine. The research could weave us a little closer to a strong and flexible biomimetic material.

High-resolution nuclear magnetic resonance (NMR) spectroscopy and photoinduced electron transfer fluorescence correlation spectroscopy (PET-FCS) have been used to show how protein dynamics in spider silk is mediated by the amino acid methionine. The research could weave us a little closer to a strong and flexible biomimetic material.

Spider silk is comprised of fibre-forming proteins secreted from the arachnid's spinneret gland. Researchers from the universities of Mainz and Würzburg in Germany, have discovered that an amino acid building block other than leucine, methionine, is present in a high proportion in some spider silk proteins. This is something of a surprise, as leucine seems to the perfect evolutionary choice given its properties of hydrophobicity and its ability to form strong chains.

Nevertheless, methionine side chains are highly flexible. "It was this abundance of methionine in the spider silk protein that made us take a closer look at its dynamics," explains Ute Hellmich of Johannes Gutenberg University Mainz (JGU). His team collaborated with Hannes Neuweiler at Julius-Maximilians-Universität Würzburg (JMU) to glean the details using state-of-the-art biophysical tools.

The JMU team substituted the amino acid methionine systematically in spider silk proteins, replacing leucine and the studies the protein folding, stability, and dynamics of the variants using PET-FCS and NMR. The data obtained using these two techniques gave rise to the unexpected conclusion that methionine in spider silk protein increases the flexibility of the protein structure, and that this flexibility is precisely what enables the individual proteins in spider silk to interact closely.

Substitute

"We found that substituting methionine with leucine has no effect on the spider silk protein structure," explains JGU team member Benedikt Goretzki. "In fact, both proteins look exactly the same. At the same time, however, the natural methionine-containing protein binds much more strongly to other spider silk proteins." He adds that "We were really amazed as this shows that it is not just the shape of a protein that determines how it functions but also, to a considerable degree, its flexibility."

JMU team member Julia Heiby adds that "Methionine not only makes the protein more dynamic, it also improves its functionality. In effect, it enables two proteins to specifically interlink with each other, which would otherwise be impossible, even if they had the same structure."

Weaving new materials

Biologists usually assume that when it comes to proteins, and indeed other biomolecules, form follows function. If one knows the detailed three-dimensional structure, it is usually possible to ascertain the function of that structure. However, this generalisation does not always hold true and it is possible for nature to exploit dynamics to adjust functionality. The research suggests that it might be possible to selectively adjust the properties of spider silk proteins by suitable amino acid substitutions. It may even be possible to generate entirely novel and yet highly strong and stable biomaterials. The two research groups are hoping to also offer new insights into the relevance of protein dynamics with respect to biological function in a more general form. "Protein dynamics are important in all aspects of life," adds Hellmich. "This is true for both spiders and humans."

Related Links

Nature Commun 2019, online: "Methionine in a protein hydrophobic core drives tight interactions required for assembly of spider silk"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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