Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Why spiders don't drop off of their threads

18.08.2011
The source of spider silk's extreme strength unveiled

"The strength of spider dragline silk exceeds that of any material produced in laboratories, by far. All attempts to manufacture threads of similar strength have failed thus far," explains Professor Horst Kessler, Carl von Linde Professor at the Institute for Advanced Study at the TU Muenchen (TUM-IAS).


In collaboration with the workgroup of Prof. Thomas Scheibel, who was a researcher at the TU Muenchen until 2007 and who now holds a chair of the Institute of Biomaterials at the Universitaet Bayreuth, Professor Kessler's team has been researching for years to unveil the secret of spider silk.

How do spiders manage to first store the silk proteins in the silk gland and to then assemble them in the spinning passage in a split second to form threads with these extraordinary characteristics? And what exactly gives the threads their tremendous tensile strength? Scientists have now come one step closer to answering these key questions for the production of artificial spider silk.

Spider threads consist of long chains of thousands of repeating sequences of protein molecules. These silk proteins are stored in the silk gland in a highly concentrated form until they are needed. The long chains with their repeating sequences of protein molecules are initially unordered and must not get too close to each other as they would immediately clump up. Only in the spinning passage, just before being used, are the threads oriented parallel to each other and form so-called micro crystallites that are, in turn, assembled to stable threads with cross links.

During the last year, the scientists in Kessler's and Scheibel's team investigated the common garden spider ("cross spider") to discover the mechanism behind the transition from individual spider silk molecules to connected treads: The individual spider silk proteins are first stored in the silk gland in small drops called micelles.

The scientists identified the regulating element that is responsible for assembling a strong thread from the individual parts. It is the so-called C terminal domain of the silk protein. It prevents the formation of threads in the silk duct with its strong salt concentrations. In the spinning passage, however, where the salt concentration is low and sheer forces are abundant, this domain becomes instable and "sticky." This causes the chains to overlap and a strong spider silk thread is formed. The discovery of the significance of this relatively small C terminal domain, when compared to the overall length of the protein thread, was a sensation at the time and was published in the renowned scientific journal Nature.

Now the same group of researchers has put in place a further piece in the spider silk puzzle. They showed that the other end of the long thread, the so-called N terminal domain, plays an important role in the design of strong threads with great tensile strength. This time, the scientists investigated the head ends of the spider silk proteins of the "black widow" (Latrodectus hesperus). The result: The N terminal head ends exist in the silk duct as single strands (momomers). Only in the sinning passage are the head to tail pairs (dimers) formed.

The process of laying together is regulated via the change in pH values and salt concentrations between the silk duct and the spinning canal. In the silk duct, a neutral pH value of 7.2 and a high salt concentration prevent the N terminal head ends from combining. In the spinning passage, however, the environment becomes acidic (pH value around 6.2) the salt is removed. Now the ends can come together. In this process, the N terminal ends connect to the respective other ends – a practically endless chain of linked up spider silk proteins is formed. "In our work we were able to show, in addition to our previous research, that both the pH value and the salt concentration influence the monomer-dimer balance," says Franz Hagen, corresponding author of the study, in summing up the results. "Both factors influence the formation of dimers and thus the efficient cross-linking to very long silk proteins."

Ultimately, this cross-linking is what gives the spider silk threads their enormous tensile strength. The small crystallites first formed in the parallel cross-linking of the protein chains following the controlled unfolding of the C terminal domain are connected to each other via the N terminal domains of the spider silk protein to form a very long chain. "This is the effect that eventually explains the enormous tensile strength of the spider silk thread," says Kessler. To date, this ingenious form of cross-linking – called "multivalence" – has not been implemented in artificial polymers. "Most polymer chemists focus on the length of the thread. So far, no one has come up with the approach of cross-linking the ends of the threads and thereby opening the door to virtually unlimited lengths of polymer chains," beleives Kessler. These new findings may provide chemists with a model for manufacturing new materials with improved characteristics.

The scientists used the method of nuclear magnetic resonance (NMR) to analyze the structure of spider silk. Segments of spider silk are dissolved under conditions similar to those found in spider organs and exposed to radio wave impulses in a very strong magnetic field. The scientists can deduce the exact molecular structure from the "response" of the molecules. Using this method, environmental influences (e.g. salt concentration and pH value) can be studied accurately under simulated natural conditions. The development and application of NMR methods to biomolecules has been a longstanding focus of the Bavarian NMR Center in Garching.

Dr. Markus Bernards | EurekAlert!
Further information:
http://www.tum.de

Further reports about: protein molecule silk protein spider silk tensile strength

More articles from Materials Sciences:

nachricht Meter-sized single-crystal graphene growth becomes possible
22.08.2017 | Science China Press

nachricht Nagoya physicists resolve long-standing mystery of structure-less transition
21.08.2017 | Nagoya University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Cholesterol-lowering drugs may fight infectious disease

22.08.2017 | Health and Medicine

Meter-sized single-crystal graphene growth becomes possible

22.08.2017 | Materials Sciences

Repairing damaged hearts with self-healing heart cells

22.08.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>