Spider gene unravelled
scientists in the us have unravelled the genetic structure of one of the strongest silks that spiders produce. The discovery could help make super spider-silk products with a wide range of defence, industrial and medical applications.
University of California, Riverside professor Cheryl Hayashi and her postdoctoral student Jessica Garb studied the protein used to make silken egg cases in female spiders from 12 species. They found striking similarities in the lengthy amino acid sequences of the protein, tusp 1, in all species studied. These sequences determine such properties of the spider silk as elasticity, tensile and breaking strength. The findings appeared in the August 1 early edition of the journal, Proceedings of the National Academy of Sciences.
"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." Commercial silk, typically harvested from cocoons of the silk moth, is only one-third as strong and about half as elastic as spider silk.
After identifying the protein responsible for the silk used to make egg cases, the scientists uncovered its molecular composition. This is particularly important as spider webs cannot be harvested from large farms of cohabiting critters, unlike silk from silkworms. Most spiders are territorial and cannibalistic and would kill each other before spinning enough silk to make marketable products. Consequently, an option available to scientists is to introduce the gene in another host organism, which can produce copious amounts of the protein that can be harvested in large quantities.
Scientists don't know much about the mechanical properties of egg case silk yet. But the University of California scientists hypothesise that it might have unique properties based on its ability to protect hundreds of eggs. One possible trait, they say, is the ability to block ultraviolet radiation, which could be useful for future spider silk applications.
Spiders produce about seven different types of silk to move, trap and store food, and to reproduce. The silk threads are spooled out of spinnerets, the external parts of silk glands. Spiders often have numerous pairs of spinnerets, which they use to produce different types of silk. 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.
"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 in a statement issued by the university. "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 and parasites."
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