Simulating protein control of Calcite Crystallisation by Ovocleidin-17

Lead Research Organisation: University of Warwick
Department Name: Chemistry

Abstract

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.

Publications

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Freeman CL (2010) Structural control of crystal nuclei by an eggshell protein. in Angewandte Chemie (International ed. in English)

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Freeman CL (2010) Structural control of crystal nuclei by an eggshell protein. in Angewandte Chemie (International ed. in English)

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Quigley D (2009) A metadynamics-based approach to sampling crystallisation events in Molecular Simulation

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Quigley D (2009) Metadynamics simulations of calcite crystallization on self-assembled monolayers. in The Journal of chemical physics

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Quigley D (2011) Sampling the structure of calcium carbonate nanoparticles with metadynamics. in The Journal of chemical physics

 
Description The protein ovocledin-17 has been shown to modify the growth of calcite in laboratory studies and has been identified as one of the possible controls of eggshell growth in chickens. Our simulations modelled the effect of the protein on the crystallisation of calcium carbonate and showed two main effects. First, the crystal structure of calcium carbonate nanoparticles depends on the particle size with potentially no structure at small sizes. Second, we demonstrated that the presence of the protein could control the preferred structure of the calcium carbonate. These were used to develop a model of how the protein could generate calcite nanoparticles through a quasi-catalytic process as the first stage in the formation of chicken eggshells in vivo. These simulations demonstrated the power of a new technique (metadynamics): to generate free energy surfaces for complex systems; and to make it routine to find and simulate rare events such as crystal nucleation. It aslo demonstrated the need for a national supercomputer, being one of the first major applications to require the power of HECToR when it was first installed.
Exploitation Route The understanding of how proteins can control the size and shape of crystals is essential to the understanding of biomineralisation; the fundamental process whereby organisms make minerals. If we can understand the essential features that these molecules must possess to be able to control mineral characteristics, this would enable synthetic chemists to design molecules to make nanostructures with particular structures and properties. This is the goal of biomimetics; whereby ideas are taken from natural processes to develop new methods of synthesising complex structures.
Sectors Agriculture, Food and Drink,Chemicals,Education,Environment,Healthcare

 
Description Major publications from this grant have been well cited in the literature. The techniques have been used by the investigators in other research they have conducted since, particularly relating to biomineralisation. Following initial publication, the work made a major impact on the media, including radio interviews with the BBC, ABC (Australia), and various other countries including an interview on live radio in Columbia
First Year Of Impact 2010
Sector Chemicals,Education
Impact Types Societal