Age-old puzzle cracked

Scientists have cracked the puzzle of what came first – the chicken or the egg. The answer is both after research showed a particular chicken protein acts as a catalyst in egg shell formation.

Researchers had long known that a chicken eggshell protein – ovocledidin-17 or OC-17 – must play a part in shell formation as it is only found in the mineral region of the egg, and lab tests showed that the protein influenced the transformation of calcium carbonate into calcite crystals.

But how this was controlled was unclear so researchers from the Universities of Sheffield and Warwick applied metadynamics – a powerful computing tool used by the UK national supercomputer in Edinburgh– to create simulations showing how the protein binds to amorphous calcium carbonate.

“Metadynamics extends conventional molecular dynamics simulations and is particularly good at sampling transitions between disordered and ordered states of matter,” said Dr David Quigley from the department of physics and centre for scientific computing at Warwick.

The simulations showed that the protein binds to the calcium carbonate surface using two clusters of arginine residues which are located on two loops of the protein. This creates a chemical clamp to nanosized particles of calcium carbonate which encourages calcite crystallites to form. Once the crystallites reach a large enough size to grow under their own steam, the protein drops off to kickstart crystallisation elsewhere. This leads to an 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,” said Professor John Harding from the department of engineering materials at Sheffield, “Nature has found innovative solutions that work for all kinds of problems in materials science and technology – we can learn a lot from them.”