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How soft corals defy their environment: Protein favors calcite formation in aragonite sea

Date:
August 16, 2011
Source:
Ludwig-Maximilians-Universitaet Muenchen (LMU)
Summary:
Many marine organisms, including corals, build skeletons from calcium carbonate – in the form of calcite or aragonite. The current composition of seawater favors the formation of aragonite – but soft corals have a specific protein that allows them to form calcite skeletons instead.

Many marine organisms, including corals, build skeletons from calcium carbonate -- in the form of calcite or aragonite. The current composition of seawater favors the formation of aragonite -- but soft corals have a specific protein that allows them to form calcite skeletons instead.

Calcium carbonate is a salt for all seasons. It turns up not only in marble, but also in biogenic sediments such as limestone and coral reefs -- and even in pearls. The compound exists in two major crystalline forms, as calcite or aragonite. However, it is not clear what determines which variant an organism will exploit under conditions in which both forms can precipitate.

A team of researchers led by LMU geobiologist Dr. Azizur Rahman, who is also a Research Fellow of the Alexander von Humboldt Foundation, has now answered this question, in collaboration with colleagues based at the University of the Ryukyu Islands in Japan.

Together, the scientists have shown that, in the soft coral species Lobophytum crissum, a secreted, extracellular protein known as ECMP-67 is the decisive factor that results in the precipitation of calcite, irrespective of the chemical conditions prevailing in the surrounding seawater.

"Over the course of Earth's history, and most probably depending on the relative amounts of dissolved magnesium and calcium ions, either calcite or aragonite has dominated in the world's oceans," says Professor Gert Wφrheide, one of the authors of the new study. Current conditions favor the formation of aragonite, and many stony corals build their skeletons exclusively from this material. However, thanks to ECMP-67, Lobophytum crassum can still produce calcite in an aragonite sea.

"We have also been able to show how the extracellular protein ECMP-67 contributes to the production of calcite at the molecular level," says Rahman. "These findings should also allow us to elucidate the crystal structure of calcite in natural environments."

The study was funded by the Alexander von Humboldt Foundation and the Japanese Society for the Promotion of Sciences.


Story Source:

The above story is based on materials provided by Ludwig-Maximilians-Universitaet Muenchen (LMU). Note: Materials may be edited for content and length.


Journal Reference:

  1. A. Rahman, T. Oomori, G. Woerheide. Calcite formation in soft coral sclerites is determined by a single reactive extracellular protein. Journal of Biological Chemistry, 2011; DOI: 10.1074/jbc.M109.070185

Cite This Page:

Ludwig-Maximilians-Universitaet Muenchen (LMU). "How soft corals defy their environment: Protein favors calcite formation in aragonite sea." ScienceDaily. ScienceDaily, 16 August 2011. <www.sciencedaily.com/releases/2011/08/110816120828.htm>.
Ludwig-Maximilians-Universitaet Muenchen (LMU). (2011, August 16). How soft corals defy their environment: Protein favors calcite formation in aragonite sea. ScienceDaily. Retrieved July 25, 2014 from www.sciencedaily.com/releases/2011/08/110816120828.htm
Ludwig-Maximilians-Universitaet Muenchen (LMU). "How soft corals defy their environment: Protein favors calcite formation in aragonite sea." ScienceDaily. www.sciencedaily.com/releases/2011/08/110816120828.htm (accessed July 25, 2014).

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