Biologists Crack Genetic Code for Specialized Spider Silk

11 August 2005

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 discovery will help biotechnologists develop applications for spider silk and will shed light on spider evolution.

Assistant Professor of Biology Cheryl Hayashi and postdoctoral researcher Jessica Garb characterized the variants of the protein (TuSp1) used by 12 species of spiders to make egg-case silk. They found strong similarities in the lengthy amino acid sequences of the proteins among species that diverged at least 125 million years ago.

Garb and Hayashi published their findings in the Aug. 1 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.

The findings are important, in part, 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.

“Collectively, spider silks are some of the toughest natural fibers 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 armor, 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. Of the seven types of silk spiders produce, the fibers used to encase spider eggs are of exceptional strength and durability.

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