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Thursday, Jan. 17, 2002
What webs we weave
By ROWAN HOOPER
Spiderman might still be the stuff of comic books, but spidermammals exist, and they are this week the stuff of science journals.
The reason? Spidermammals (of a sort) have been created to produce spider silk, a material that has long been the holy grail of biotechnology researchers. The silk, spun by common garden spiders, is a nanofiber one-tenth the width of a human hair -- but strong enough to stop a bee flying at 30 kph. It's so tough, it has been suggested that a pencil-thick strand would halt a Boeing 747 mid-flight. Stop a speeding bullet? No problem.
The properties of spider silk are extraordinary and its potential therefore vast. A ready supply would allow for revolutionary eye- and neurosurgery procedures, lightweight parachutes and seat belts, rust-free bumpers and paneling for cars, biodegradable fishing lines, artificial tendons and ligaments, and (the one that has military and police authorities drooling) soft body armor, five times stronger by weight than steel.
The grail is now in sight, and -- not surprisingly with a market estimated to be worth $2 billion -- it already has a trademark: BioSteel. A team of researchers in North America has succeeded in inserting spider-silk genes into mammalian cell lines, enabling them to secrete water-soluble silk proteins. The team spun the silk and produced a material comparable in strength to natural spider silk.
Anthoula Lazaris headed the group of scientists, from Nexia Biotechnologies Inc. in Montreal and from the U.S. Army Soldier Biological Chemical Command in Natick, Mass. Their results are published today in Science.
Spiders use silk for constructing the web frame, wrapping prey and egg sacs, as a life-line, as a shelter and during sperm transfer. Different types of silk are used for different functions, and it is the frame silk, or dragline silk, that has been most sought after. This stuff is tougher than the current best high-performance synthetic fibers, including Kevlar and aramid, which are made using toxic chemicals.
The problem is that, unlike silkworms (the larvae of the silk moth), spiders can't be farmed. Their strong territorial behavior and tendency to cannibalize each other has precluded their domestication.
So scientists and biotech firms hungry for superfibers have had to come up with other ways of producing them. Their first efforts involved inserting silk genes into bacteria, but bacteria are primitive organisms and can't properly express long genes: They ended up producing silk proteins shorter than normal. Such "truncated" silk was inferior to natural spider silk.
Spider genes inserted into mammalian cells, however, produce the goods. Lazaris and colleagues created lines of cells (derived from cow and hamster kidneys) containing silk genes from two species of orb-web weaving spiders. Meanwhile, Nexia has made transgenic goats expressing the silk genes. Goat mammary glands and spider silk glands are similar in that they both manufacture and secrete complex, water-soluble proteins in large amounts. Silk/milk production by Nexia's transgenic goats is scheduled to begin in the second quarter of this year.
Biotechnology is starting to fulfill its awesome potential, which might explain why the Science paper almost reads like something out of a William Gibson novel. Biotechnology is essentially concerned with using nature as a model for solving human problems.
But this is only the beginning. The transfer of beneficial genetic traits from one species to another using molecular biology is becoming commonplace. In the next few years, we can expect more transgenic marvels.
"These results are remarkable," said Costas Karatzas, one of the paper's authors and vice president of research and development at Nexia. "We were able to produce monomers [simple molecules] and spin fibers in an aqueous environment, thereby mimicking the spider's way of spinning silk, a process that has been perfected through 400 million years of evolution.
"Using these water-based BioSteel solutions for large-scale fiber spinning would be considerably more environmentally friendly than using harsh solvents such as those used for most synthetic fiber manufacturing."
Not only is the production "green," but the products will be, too: hence biodegradable fishing line and medical sutures. This might be a key selling point for a public uncertain about the concept of spidermammals.
E-mail Rowan Hooper at rowan@ japantimes.co.jp