Monday, 16 April 2012



 


Spider Silk (without the spiders....) 

Simon Neil


Spider silk; it's pretty amazing stuff. It's lighter and tougher than Kevlar fibre, stronger per unit weight than steel, and its amazingly flexible. Materials scientists have long seen it as their Holy Grail, as ropes, cables and cloth made from spider silk would have unbelievable mechanical strength and be resistant to extreme stresses. The biggest obstacles to obtaining the miracle material are the spiders themselves.

People have attempted to farm spiders for their silk before, but have always met with disastrous results. Spiders tend to be extremely territorial, and when forced into close proximity with one another they quickly kill each other, much to the horror of the investors in these expensive schemes. In fact, only one piece of cloth has ever been made entirely from spider silk. It took 70 people 5 years to collect the golden orb spiders needed, and a further 4 years to produce the four meter long fabric.
In order to overcome this highly labour intensive problem, a collaborative research effort between the University of Wyoming and scientists working for Nexia Biotechnologies decided to try and combine the genes that code for spider silk into the genome of dairy goats. This is a technique from molecular biology known as recombinant cloning. After intensive research, the targeted spider genes from a common orb-weaving spider Nephila clavipes were sequenced by Dr Randy Lewis in 1993.
These genes were then isolated using endonuclease enzymes that 'snip' the DNA at very specific regions, leaving 'sticky ends'. By using a similar process to remove the goat genes that code for one of the proteins normally present in their milk, the researchers provided an opening to insert the spider genes. The sticky ends of both fragments are 'complimentary' and overlap, forming hydrogen bonds. DNA ligases come in and join the phosphate backbones of the strands together again, and the new gene is incorporated into the genome.
The molecular structure of the silk proteins is what underlies its incredible mechanical properties. The proteins have a kind of mosaic pattern that Dr Lewis described as a "Lego and Slinky" motif. The protein called Spidrion 1 is made from repeating, alanine rich peptide residues that make hard, crystalline regions in the overall structure. These are joined together by amorphous regions of glycine rich residues. This pattern of hard crystals separated by spongy amorphous protein blobs make spider silk a liquid crystal, and is what makes the stuff the toughest biological material known to man, while still being lightweight and flexible.
Genetically altered chimeric goats don't come cheap, although the financial details are kept confidential by Nexia Biotechnologies and their recent parental company PharmAthene. Despite this, the process is commercially viable, as one litre of goats milk will produce an astounding 9000 metres of silk. The silk is manufactured into a variety of products, including medical sutures, biodegradable fishing line, artificial ligaments and lightweight ballistics armour. There are also plans to use it to create super high tension cables for offshore oilrig moorings, and even considerations to use it as tethering for space elevator projects!

For more information, try here: Nexia Fact Sheet

References

Kluge, JA, Rabotyagova, O, Leisk, GG, Kaplan, DL 2008, ‘Spider silks and their applications’, Trends in Biotechnology, vol. 26, no. 5, pp.244-55, viewed 15 March 2012, http://dx.doi.org/10.1016/j.tibtech.2008.02.006
Form 2A 2007, listing statement, Nexia Biotechnologies LTD, viewed 17 March 2012, http://www.cnsx.ca/Storage/1080/95750_Listing_Statement.pdf
Lazaris, A, Arcidiacono, S, Hyang, Y, Zhou, JF, Duguay, F, Chretien, N, Welsh, EA, Soares, JW, Karatzas, CN 2002, ‘Spider Silk Fibers Spun from Soluble Recombinant Silk Produced in Mammalian Cells’, Science, vol. 295, pp.472-76, viewed 14 March, 2012, <http://frank.itlab.us/photo_essays/papers/spinning_spider_silk.pdf>  DOI 10.1126/science.1065780
Lewis, R 1996, ‘Unraveling the weave of spider silk’, BioScience, vol. 46, no. 9, pp.636-38, viewed 15 March 2012, http://www.jstor.org/stable/1312891
Nexia Biotechnologies 2002, fact sheet, Office of Technology Transfer, MacGill University, viewed 14 March 2012, http://www.mcgill.ca/files/ott/nexia.pdf

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