Spider silk is one of the toughest fibres in nature and has astounding properties. Spider silk shows different responses to different levels of stress. With small insects and light winds, spider silk can yawn and regain its former form, while in strong storms the most yawning sections can harden and break. They are highly extensible and strong, lightweight, almost invisible, and of course biodegradable: the threads spiders use to build their webs. Why spider silk is so incredibly tough? What is in the structure of spider silk? Why are the lightweight silk threads of web spiders tougher than most other materials? Can spider’s silk be produced synthetically? New research finally explains why spider’s silk is so incredibly tough.
Why are the lightweight silk threads of web spiders tougher than most other materials?
Spider webs consist mainly of silk threads. These very thin yarns, besides being light and flexible, have a stronger structure than high-quality steel.
For this reason, researchers are trying to better understand the structures of spider fibres. They continue to produce them synthetically to ensure industrial use of these superior-grade materials, which have a wide range of usage potential, from surgical yarns to military clothing.
Synthetic spider silk is already produced on an industrial scale and used in various products. But it is far from being able to imitate the excellent mechanical properties of the natural. The latest findings of the researchers in Würzburg might contribute to eliminating the shortcomings.
Scientists from the University of Würzburg have discovered that spider’s silk contains an exceptional protein and has published in Nature Communications.
Structure of spider silk
Its life depends on protein. 20 different amino acid types play a role in protein synthesis in living organisms. The number and sequence of these amino acids determine the properties of the protein. After being synthesized as linear chains of amino acids, most proteins fold into highly ordered, three-dimensional structures.
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Natural amino acids can be roughly divided into two groups based on the properties of their side chains.
So-called hydrophobic side chains have a low solubility in water. They are often located in the core of a protein and stabilize the folded state.
Hydrophilic, side chains tend to be on the surface of the protein where they are responsible for an almost unlimited variety of functions.
When hydrophobic amino acids such as leucine (which do not like water) are located at the center of the protein structure, high strength yarn can be obtained. Therefore, the strong structure of spider silk was thought to be caused by the amino acid leucine.
But the researchers found that the spiders used a specific amino acid called methionine to tightly bind silk proteins in a way previously unknown.
Methionine belongs to the hydrophobic group of amino acids (which do not like water). It is also known that the side chain of methionine is extremely flexible compared to the side chains of 19 other natural amino acids. But it rarely appears in most proteins. So far, molecular biologists and scientists have paid little attention to this amino acid.
Scientists at the University of Würzburg systematically replaced the methionine amino acids in spider silk proteins with leucine and observed the results.
They found that the protein had a flexible structure thanks to the side chains of the methionine amino acid. They found that the interaction between the protein chains increased as a result of this, making the chains bind to each other.
At the end of this research, they found that the superior mechanical properties of spider silk were revealed by the amino acids of methionine.
How Does The Amino Acid Methionine Affect Materials Science?
Considering that one of the hardest materials in nature is spider silk, we can encounter countless potential applications in material science when we better understand the unique properties of this material, which combines industrial flexibility and durability.
Therefore, in the sense of the development of materials science, the discovery that the amino acid methionine in silk proteins provides tight interactions between spider’s silk proteins is of great importance.
The mechanical properties of the synthetic material to be produced can be adjusted according to the need by changing the methionine content in the protein. In this way, technological products with the desired properties can be obtained.