Spiders are remarkable animals: with over 40,000 classified species, they are among the most diverse known to man and can adapt to the most radical climatic conditions. The silky substance they produce to spin webs has been extensively studied and is known to rival steel in strength: a less-known fact, however, is that the "glue" that holds it all together is just as remarkable, and could soon become the key to producing stronger bioadhesives to replace petroleum-based products.
Supported by the National Science Foundation, a team led by Omer Choresh from the University of Wyoming has in fact recently reported on an extensive study involving the DNA sequencing of the orb-weaving spiders Nephila clavipes and Araneus gemmoides. The group identified two sophisticated proteins that have evolved over millions of years and are believed to be responsible for the glue's strength.
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The team extracted m-RNA — a type of RNA cell containing the chemical blueprint for a protein — from the glue-secreting glans of the spiders, and created a complementary DNA sequence to identify what genes were responsible for the creation of the glue.
By doing so, the researchers were able to isolate two distinct but functionally related genes that were encoded on the spider's genome in an unusual way, using both strands of an identical DNA sequence. Each of these genes is responsible for the formation of a protein, and these two proteins are in turn the building blocks of the sticky glycoprotein that binds the web's threads together.
It's still unclear why the two genes have perfectly identical DNA in their repetitive regions; on the other hand, the group found strong evidence that this is a vital requirement to the glue's strength as both species examined have maintained the identity of these sequences despite over 100 millions of years of separation. In other terms, it's a case of evolutionary convergence rather than something due to chance alone.
Now that these important facts have been uncovered, the next step will be to clone the two genes and employ them in bacterial cell cultures to obtain large-scale production of the glycoprotein. This will allow us to develop a new biobased glue for a variety of purposes, including stronger surgical adhesives.
A report on the study was published the October issue of the monthly journal ACS Biomacromolecules.