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The July 27 issue of Proceedings of the National Academy of Sciences USA reports that a group of Korean researchers led by Sang Yup Lee (with an assist from David Kaplan at Tufts) were able to synthesize spider web fibers very much like the ones found in nature by using recombinant Escherichia coli.  

People have been trying to do this for some time because spider web material is notoriously strong and flexible, actually much better in that regard than even Kevlar.  Not only that, but it’s a renewable, biodegradable material.  Most polymers are made from petroleum, and most of them are not biodegradable; they sit in landfills (or worse, the ocean) for centuries.

Unfortunately, spiders don’t willingly sit there and spin webs for you.  In fact, they’re pretty easy to tick off.  So there has been a years-long effort to use genetic engineering to get a simpler and friendlier organism to do it for us, like a nonpathogenic microorganism that can be fed sugar in a simple bioreactor.  But the closest researchers had gotten up to now was a variety of inferior materials with low molecular weight that were simply not ready for prime time.

Spider web fibers are made of two kinds of proteins called spidroins.  They’re huge proteins, and they’re also very repetitive in sequence.  The repetitive parts contain a very high proportion of the amino acid glycine.  If you want your organism to make lots of spider-web material, you’ll need them to make a lot of glycine, and most organisms just aren’t up to the task.

Happily, we know a lot about the metabolism of E. coli.  It is always present in our colons (usually quite harmlessly), and so we’ve been studying it for a very long time.  The Korean researchers were able to amp up glycine production in E. coli by dialing up the metabolic pathway that produces it with a little genetic engineering.  But they were also able to increase E. coli’s ability to get all that glycine into protein by also dialing up the pathway that produces the transfer RNA responsible for linking glycine to a growing protein chain.

These metabolic tricks allowed the spider silk proteins to reach five times the molecular weight of any previous attempt.  And that made all the difference in the properties of the silk.  When spun into fibers, they behaved much like real spider silk.

There is one news report today of this, and it does use a picture.  (I'm not copying anything right from the journal.)  So go to medgadget.comfor their take on it.  I'll replicate this picture (an electron micrograph of the high-molecular-weight fiber) here.

Originally posted to skralyx on Wed Jul 28, 2010 at 03:09 PM PDT.

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