Rutgers researchers uncover how stony corals form strong skeletons

Corals are colonies of tiny, genetically identical animals known as polyps that form their characteristic skeletons by combining the mineral calcium carbonate with fibers of living matter, in a process known as biomineralization. But how the skeletons of stony corals arrange scores of different proteins in the process of biomineralization has been largely unknown.

New research now sheds light on the spatial interaction of the proteins in the skeleton of the common Indo-Pacific stony coral Stylophora pistillata. The research, led by Dr. Paul Falkowski and Manjula P. Mummadisettia at Rutgers University in New Jersey, appears in the Journal of the Royal Society Interface, Feb. 24.

The researchers set out to identify the spatial arrangement of the different proteins embedded in the coral skeleton and how the proteins interact with each other. 

"These spatial arrangements clearly show that protein–protein interactions in coral skeletons are highly coordinated and are key to understanding the formation and persistence of coral skeletons through time," the researchers said.

The spatial network of proteins is important in understanding how the coral skeleton becomes rock-hard. The researchers mapped the protein-protein interactions using chemical cross-linking and mass spectrometry sequencing.

They prepared, cleaned and powdered coral skeleton and then used chemical cross-linking with high resolution mass spectrometry to see how the proteins were connected. Cross linking is the chemical joining of molecules, with a a cross-linking reagent such as bis(sulfosuccinimidyl)suberate (BS3). It is frequently used to study protein interactions. 

The researchers then used their data to generate a map of the interaction networks of the proteins. Each protein became a node on the map, with interactions depicted by lines going to other nodes. The lines represent the biochemical interactions in skeleton material formation.

Some of the important proteins identified are coral acid-rich proteins, known as CARPs, carbonic anhydrases, and several calcium-binding proteins.

The researchers suggest a working model of biomineralization in stony coral where a framework is built by various adhesion proteins. Then calcium-binding proteins, including some CARPs and carbonic anhydrase, are recruited. Magnesium-rich calcium carbonate is nucleated, and four calcium-binding proteins are recruited, followed by the formation of needle-like aragonite crystals. Aragonite is a crystalline form of calcium carbonate.

The importance of corals

Stony corals are marine invertebrates that form enormous reefs in tropical and subtropical oceans. These reefs are important geologically and ecologically as they offer protection to shorelines from erosion and storms as well as providing a habitat for fish. 

One of the underlying questions of the study is how coral biomineralization, the growth process of corals, will be affected by climate change.

“Our findings suggest that corals will withstand climate change caused by human activities, based on the precision, robustness, and resilience of their impressive process for forming rock-hard skeletons,” said Paul Falkowski, senior author, in a news release on the research. Falkowski is a distinguished professor in the School of Environmental and Biological Sciences at Rutgers University–New Brunswick.