May 17, 2010 | David F. Coppedge

Like Magic: Spiders Convert Fluid to Steel-Strong Silk

How do they do it?  Spiders spin their webs with such ease, but scientists know they are working a kind of material magic.  Inside the storage sac, the proteins act like a fluid.  Outside the spinnerets, that fluid turns into a structural rope that is stronger than steel, but elastic enough to absorb the energy of an insect.  They would sure like to imitate that feat.  Some steps toward understanding the transformation from liquid to strong fiber were announced in Nature this week, and summarized on Science Daily.
    The trick goes all the way down to the molecular level.  The proteins line up in the liquid state in such a way that their cross-bridges are unable to form the strong, taut chains that will characterize the silks in the spider web.  Once the liquid goo enters the reaction chamber, the salinity changes, the pH changes and the pressure changes.  Strong shear forces are set up.  This breaks salt bridges and allows the molecules to realign.  “The long protein chains are aligned in parallel, thus placing the areas responsible for interlinking side by side,” Science Daily reported.  Presto: “The stable spider silk fiber is formed.”  Like magic, this all happens in split seconds.  The spinneret is quicker than the eye.  In one of the papers in Nature,1 the scientists said, “Our study provides an important stepping-stone for further understanding of the remarkably fine-tuned process of spider silk formation.”  The other paper discussed the “controlled switching between the storage and assembly forms of silk proteins” that prevent premature aggregation and denaturation, such that they can be “transformed into extremely stable fibres on demand.”2
    Scientists can hardly wait to learn how the trick is done.  “The potential applications are countless, from resorbable surgical suture material to technical fibers for the automotive industry.”  Most people probably never dreamed that the spiders in their garden held such secrets to a bright future.

1.  Askarieh et al, “Self-assembly of spider silk proteins is controlled by a pH-sensitive relay,” Nature 465, 236-238 (13 May 2010), doi:10.1038/nature08962.
2.  Hagn et al, “A conserved spider silk domain acts as a molecular switch that controls fibre assembly,” Nature 465, 239-242 (13 May 2010), doi:10.1038/nature08936.

This is just another in a long-running series about spider silk.  It highlights a common theme: the wonders of nature – things all around us – are more amazing than we imagine.  Understanding their design (not their presumed evolution, a useless distraction*) is the key to scientific advancement and progress – measured in ways that can enrich our lives.
*Only one of the papers in Nature even mentioned evolution – and that was to say, “The overall dimeric structure and observed charge distribution of NT is expected to be conserved through spider evolution and in all types of spidroins.”  Conserved means un-evolved.  The paper had a lot to say about structure and function, though.  Evolutionary theory contributed absolutely nothing to the research.

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