Simulating protein control of Calcite Crystallisation by Ovocleidin-17

Eggshells in birds are made of about 95% calcium carbonate, with a matrix of proteins which both controls how the crystals are laid down and prevents the shell from becoming too brittle. The process is very fast - a hen can make an egg in about 20 hours. The shell itself has a complicated structure whose features are essential for the health of the embryo it contains. Recent experimental data have identified several proteins associated with the formation of egg shells. One class of proteins (C-type lectin-like proteins) appears to be particularly important in controlling calcite deposition for various bird species, although how the proteins do this is not well understood. Studies with ovocleidin-17 (chicken) and ansocalcin (goose) have showed that these proteins both encourage crystals to form and have a strong effect on their growth and shape. Simulations are essential to understand how this happens. We will model the interaction between ovocleidin-17 and various CaCO3 surfaces in the presence of water. This will enable us to understanding what parts of the molecule determine the shape of the crystal and why they are important. A particular highlight will be the use of metadynamics on HECToR to determine how ovocleidin-17 affects the free energy of amorphous calcium carbonate particles and their transformation to a crystalline phase. These simulations will provide extremely valuable information for experimental groups seeking to design new molecules to produce particular crystal types and shapes. This is part of biomimetics, the strategy of using biological ideas to guide the search for new materials and processes.