Seminar Details

The mechanism of aragonite precipitation in corals




Dr. Tali Mass - The Leon H.Charney School of Marine Sciences, University of Haifa


Atmospheric CO2 levels are rising rapidly, resulting in a decrease in both oceanic pH, and the carbonate saturation state (Ω). It has been hypothesized that calcifying marine organisms, including reef-building corals, will be affected by the decline of the carbonate saturation state. However, the lack of a mechanistic understanding of processes that lead to and control calcification limits our ability to predict the response of corals to increasing atmospheric CO2. To address this question we have investigated both the structural framework proteins and the role of highly acidic proteins in nucleation and crystal growth. We established cell cultures and sequenced the genome of the stony coral, Stylophora pistillata. This genome contains 21,678 predicted protein-coding genes. With these predicted genes we used LC-MS-MS to sequence soluble and insoluble organic matrix proteins. In addition, we identified, cloned, and characterize four highly acidic proteins, derived from expression of genes obtained from the common stony coral, Stylophora pistillata. Each of these four proteins spontaneously can catalyze the precipitation of calcium carbonate in vitro. Our results demonstrate that coral acid-rich proteins (CARPs) not only bind Ca2+ stoichiometrically but also precipitate aragonite in vitro in seawater at pH 8.2 and 7.6 via an electrostatic interaction with protons on bicarbonate anions. Based purely on thermodynamic grounds, the predicted change in surface ocean pH in the next decades would appear to have minimal effect on the capacity of these acid-rich proteins to precipitate carbonates.

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