Experts apply new technique to crack egg shell problem

Researchers at the Universities of Sheffield and Warwick have applied computing power to provide an insight into egg shell formation. The work may also give a partial answer to the age old question "what came first the chicken or the egg?"

The researchers found that 'chicken', or at least a particular chicken protein, came first in this context. There is however a further twist in that this particular chicken protein turns out to come both first and last. That neat trick it performs provides new insights into control of crystal growth which is key to egg shell production.

Researchers had long known that a chicken eggshell protein called ovocledidin-17 (OC-17) must play some role in egg shell formation. 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.

The research teams from Sheffield and Warwick have now been able to apply a powerful computing tool called metadynamics along with the UK national supercomputer in Edinburgh to crack this egg problem.

Using these tools 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. But they also noticed that sometimes this chemical clamp didn't work. The OC-17 just seemed to detach from the nanoparticle.

The researchers had therefore uncovered an incredibly elegant process allowing highly efficient recycling of the OC-17 protein. 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 crystallisation, facilitating the speedy, literally overnight creation of an egg shell.

Professor Harding, from the University of Sheffield's Department of Engineering Materials, commented: "Understanding how chickens make eggshells is fascinating in itself but can also give clues towards designing new materials and processes. Nature has found innovative solutions that work for all kinds of problems in materials science and technology – we can learn a lot from them."

Notes for Editors: The paper entitled "Structural Control of Crystal Nuclei by an Eggshell Protein" by Colin L. Freeman , John H. Harding , David Quigley , and P. Mark Rodger, is published in Angewandte Chemie International Edition, DOI: 10.1002/anie.201000679

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