Engineering Hybrid Silks

There was some big news yesterday in transgenic silk from Notre Dame and the University of Wyoming, where scientists have genetically engineered silkworms to produce silk that is a mixture of spider silk and the regular silkworm stuff. Silkworms produce the strong and versatile silk that is used to make clothes, but spiders produce silk that can be much stronger and much more elastic. Spiders, however, don't like to be grown in huge factories and don't make easily harvested cocoons like silkworms, so gathering even small amounts is very difficult (here's a fun how-to for collecting spider webs into thread). By engineering silkworms to produce spider silk it's possible to make the super-strong protein fibers at an industrial scale, for applications in medicine like super-strong sutures or tissue engineering or even to make bullet-proof vests stronger than kevlar. The engineered silkworms aren't producing 100% spider silk yet, the silkworms are instead engineered with a copy of the spider silk genes fused directly onto the end of the natural silk gene, so that the silkworm produces a silk that is a mix of the two proteins. The spider/worm silk fusion, however, does have many improved properties, and new genetic engineering technologies can potentially improve this even further and create other novel silks not found in nature.

Spider silk isn't just one kind of protein, there are thousands of species of spiders that each produce different silks for different purposes--web weaving, dragline making, egg protecting, or prey capturing. A recent PLoS ONE paper (Agnarsson et al. 2010. Bioprospecting finds the toughest biological material: extraordinary silk from a giant riverine orb spider) describes the discovery of the toughest spider silk found to date produced by "Darwin's bark spider," Caerostris darwini. These spiders form insane webs strung across whole streams, with bridgelines spanning up to fourteen meters. I don't really want to think about spiders being able to somehow fling themselves all the way across rivers on super strong silk threads, but the discovery is amazing and the potential for new biomaterials waiting to be discovered is incredible.

This kind of bioprospecting--surveying nature for compounds and materials with special properties--coupled with bioengineering for sustainable scale-up of production will make it possible to develop new silks specialized for many different purposes. From It Takes 30's post about the discovery of the new spider silk:

Agnarsson et al. argue that it is very likely that yet stronger silks remain to be discovered. The properties of spider silks have only been carefully investigated for a few species, covering only a tiny fraction of the genetic and ecological diversity of spiders. The property you want to measure also depends on the application you have in mind; if you measure toughness at two different rates of pulling, the measurements may not match, and which silk is better may also change. The authors suggest that thinking about the ecological niche a species inhabits may -- as in this case -- provide important clues to finding even more extraordinary biomaterials.

So, one day, police officers may wear (spider) silk shirts instead of Kevlar vests. Much more stylish, if a little predatory in symbolism.

(Thanks to Sri and Brady for the link and It Takes 30 for the typically fascinating post!)