July 15, 2010

Have Scientists Solved Chicken vs. Egg Debate?

Which came first: the chicken or the egg? It is an age old question that has spurred on many a debate, but now a group of scientists might actually be close to having an answer.

Using cutting-edge technology, researchers from the Universities of Sheffield and Warwick in England believe that they have discovered the answer by studying eggshells.
Scientists had long theorized that a chicken protein known as ovocledidin-17 (OC-17) played a crucial role in the formation of an egg's shell, but thanks to a new computer simulation, they were able to demonstrate the actual process.

According to a joint press release issued by both universities, "The protein is found only in the mineral region of the egg (the hard part of the shell) and lab bench results showed that it appeared to influence the transformation of (CaCo3) into calcite crystals. It remained unclear how this process could be used for forming an eggshell."

However, thanks to a new tool known as metadynamics and the assistance of the a Edinburgh-based supercomputer, "the researchers were able to create simulations that showed exactly how the protein bound to amorphous calcium carbonate surface using two clusters of 'arginine residues,' located on two loops of the protein and creating a literal chemical 'clamp' to nano sized particles of calcium carbonate"¦ While clamped in this way, the OC-17 encourages the nanoparticles of calcium carbonate to transform into 'calcite crystallites' that form the tiny of nucleus of crystals that can continue to grow on their own," according to the July 12 press release.

However, the process was not 100-percent successful, as the researchers discovered that the chemical clamp failed on occasion, as the OC-17 would just seemingly detach from the nanoparticle.

"The researchers had therefore uncovered an incredibly elegant process allowing highly efficient recycling of the OC-17 protein," claims the universities' media statement.

"Effectively it acts as a catalyst, clamping on to calcium carbonate particles to kickstart crystal formation and then dropping off when the crystal nucleus is sufficiently large to grow under its own steam. This frees up the OC-17 to promote more yet more crystallization, facilitating the speedy, literally overnight creation of an egg shell."

"Understanding how chickens make eggshells is fascinating in itself but can also give clues towards designing new materials and processes," Sheffield University Professor John Harding, one of the authors of the paper "Structural Control of Crystal Nuclei by an Eggshell Protein," said, according to a Wednesday AFP news report. "Nature has found innovative solutions that work for all kinds of problems in materials science and technology--we can learn a lot from them."

His colleague, Professor Mark Rodger of the Department of Chemistry and Centre for Scientific Computing at the University of Warwick, added "With the larger nanoparticles we examined we found that the binding sites for this chemical clamp were the same as the smaller nanoparticles but the binding was much weaker. In the simulations we performed, the protein never desorbed from the smaller nanoparticle, but always fell off or desorbed from the larger one. However in each case, desorption occurred at or after nucleation of calcite."

The paper entitled "Structural Control of Crystal Nuclei by an Eggshell Protein" by Colin L. Freeman , John H. Harding , David Quigley  , and Professor P. Mark Rodger, is published in Angewandte Chemie International Edition, DOI: 10.1002/anie.201000679  http://www3.interscience.wiley.com/journal/123506601/abstract 


Image 2: Protein attached to calcium carbonate nanoparticle.


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