Toughness of spider’s egg-case silk cracked

Toughness of spider’s egg-case silk cracked

The fibres used to encase spider eggs are exceptionally strong, durable
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Different proteins are made and mixed in silk glands to create a silk suited to each task
Egg-case silk has to last longer and must be durable
Spider silk genes are composed of long repeating sequences or modules
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A DISCOVERY that will help biotechnologists develop applications for spider silk and will shed light on spider evolution has been made.

Two biologists at the University of California, Riverside, have uncovered the molecular structure of the gene for the protein that female spiders use to make their silken egg cases.

The variants of the protein (TuSp1) used by 12 species of spiders to make egg-case silk have been characterised by Assistant Professor of Biology Cheryl Hayashi and postdoctoral researcher Jessica Garb.

Strong similarities

They found strong similarities in the lengthy amino acid sequences of the proteins among species that diverged at least 125 million years ago according to a University of California, Riverside, press release.

Garb and Hayashi published their findings in the early edition of the Proceedings of the National Academies of Science. Their paper is titled Modular Evolution of Egg Case Silk Genes Across Orb-Weaving Spider Superfamilies.

Because the mechanical properties of the various types of spider silk — their elasticity, tensile and breaking strength — are dependent on the sequence of amino acids that form the silk proteins, the findings are important.

“Collectively, spider silks are some of the toughest natural fibres known,” Hayashi said. “Imagine a fabric made from such a substance? It would be incredibly strong, flexible and ultimately, biodegradable.”

Spider silks have just begun to be considered in the improvement of a wide variety of products such as super-strong body armour, specialty rope, and surgical microsutures.

Spiders use silk to move, trap and store food, and to reproduce. Different proteins are made and mixed in silk glands, creating a silk suited to each task.

For instance, web-weaving spiders use dragline silk, which is very strong, as a frame for their wagon-wheel-like webs and a different type of silk, known as capture silk, to fill in the web.

Capture silk is more elastic than the dragline variety, and is sticky to entrap prey. The fibres used to encase spider eggs are of exceptional strength and durability of the seven types of silk spiders produce.

“The protein of the egg-case fibres has a different function altogether from that of the other silks such as dragline or capture silks,” Garb said.

“Egg-case silk has to last a long time and therefore must be durable under a wide variety of conditions, from freezing to very high temperatures. It needs to be strong enough to protect the eggs from threats such as predators, parasites and molds.”

Only partially known

Despite all this, the molecular sequences of the genes that encode spider silks are only partially known.

An example of concerted evolution, spider silk genes are composed of long repeating sequences, or modules, and a mutation in one repeat can be spread to adjacent repeats.

Cracking the molecular structure for silk is important not only for the development of products but for those who study the evolutionary biology of spiders. — Our Bureau

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