Goats And Spiders Work To Create Novel Material

By Phil Cohen, New Scientist and Angelo DePalma, BioResearch Online

By lacing goat's milk with synthesized spider proteins, researchers in Quebec plan to make an incredibly light fabric that is both biodegradable and strong enough to stop bullets. Called biosteel, it could become a green alternative to the high-strength plastics used to package shampoos or make commercial fishing nets.

Jeff Turner, president of Nexia Biotechnologies, says the biodegradable fabric would need to be sealed from the environment if used in critical applications such as body armor or spacecraft. This is because bacteria could get in and digest it.

Turner's team has already taken the first step towards creating biosteel by transferring the spider gene for the protein into goat mammary cells and collecting soluble protein from the milk. They expect genetically engineered goats to start producing the protein in the next few months.

While nobody has yet made a fabric from biosteel, Turner is convinced the protein can be turned into a supermaterial because of its natural role in the silk of a spider's web. "When you think of what a web has to do, its extreme strength makes perfect sense," he says. The silken threads of the web must be nearly invisible to prey and yet be able to bring a fly to a screeching halt.

Evolution came up with a two-pronged answer to this problem. First came a rock-solid protein, capable of making many bonds with its neighbors. Then, the spider developed a unique way of spinning the protein into a whisper-thin thread. As the spider secretes the protein solution, the silk dries and pulls taut, transforming the proteins into a nearly crystalline and completely insoluble cable. This explains why webs don't dissolve in the rain. Tests on natural silk show that it can be stronger and more elastic than high-tensile steel or the Kevlar found in body armor.

But the very properties that make silk proteins strong also make them difficult to produce. When bacteria are engineered to produce large quantities of the protein, for example, it links up in chains into a disordered, insoluble mess. The protein molecules' ability to bond with neighboring proteins (and itself) can occur in a very ordered or a disordered fashion, depending upon how the proteins fold as they form. Which is why Turner and his colleagues decided to mimic the spider's own method of production by using goat mammary cells. It turns out that the way mammals produce milk proteins and spiders make silk proteins are broadly similar. Both are produced in skin-like epithelial cells, then held in a space, or lumen, where shear stresses on the protein are minimized.

Turner cautions that the work is still in its early stages. It will take about a year before the herd of biosteel goats is large enough for Nexia's scientists to collect the protein they need to start making fabric. Then they will face the next great hurdle: how to match the spider's spinning skill. "Nature probably took a long time to get this process right," he says. "I suspect the same will be true for us."

Platform Technology

Nexia's drug and materials discovery platform consists of a patented transgenic line of goats trademarked "Bele." Bele goats were developed in order to improve the speed and efficiency of transgenic goat production. Embryos, microinjected with the DNA construct of interest, from Bele goats are transferred into standard goat recipients.

Bele goats produce recombinant protein-rich milk almost year-round.

Bele goats are year-round breeders, which allows production to continue without the summer anestrous period encountered with other breeds of goats and sheep. Plus Bele goat kids are sexually precocious. Males are sexually active as early as three months, and females are fertile at between three and six months of age. This early maturity compresses the generation interval required to generate a production herd. As a result, when using the Bele goat system, the recombinant protein of interest, purified from the milk, is available sooner.

The small physical size of Bele goats reduces feed and housing costs. The biggest expense of a ruminant transgenic program is the number of recipient animals used. The Bele goat model accelerates the breeding time and genetic progress and reduces the total cost of the transgenic program. Bele goats produce approximately 1L of milk per day for the 305-day lactation period, which is sufficient for production of kilogram quantities of recombinant proteins.

For more information: Jeff Turner, president, Nexia Biotechnologies Inc., 21,025 Trans-Canada Highway, Ste. Anne de Bellevue, QC H9X 3R2 Canada. Tel: 514-457-4522. Fax: 514-457-6151.