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Molecules and Mechanisms that Precipitate Carbonates in Corals
Reference
Mass, T., Drake, J.L., Haramaty, L., Kim, J.D., Zelzion. E., Bhattacharya, D. and Falkowski, P.G. 2013. Cloning and characterization of four novel coral acid-rich proteins that precipitate carbonates in vitro. Current Biology 23: 1126-1131.

Background
The authors write that "despite the broad interest in coral calcification and the potential for climate-driven adverse effects, the molecules and biophysical mechanism responsible for the precipitation of carbonates are poorly understood." Indeed, they say that "to date, we lack both a characterization of molecules involved in calcification and a mechanistic understanding of processes that lead to and control calcification," which "lack of knowledge limits our ability to predict the response of corals to increasing atmospheric CO2."

What was done
The seven scientists "for the first time," as they note, identified, cloned, determined the amino acid sequence and characterized four highly acidic proteins that they derived from the expression of genes obtained from the common stony coral, Stylophora pistillata, each of which proteins can spontaneously catalyze the precipitation of calcium carbonate in vitro.

What was learned
Mass et al. say their 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."

What it means
As they write in the closing sentence of their paper's abstract, the seven U.S. researchers say that "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." And as they write in the final sentence of their paper's conclusion section, they say their findings "strongly suggest that these proteins will continue to catalyze calcification reactions at ocean pH values projected in the coming century."

Clearly, the more we study them, the more we discover about the abilities of earth's many life forms to rise to the various challenges that periodically confront them as time goes by.

Reviewed 30 October 2013