Influence of Cell-free Proteins in the Nucleation of CaCO3 Crystals in Calcified Endoskeleton

Calcite and aragonite are the two common polymorphs of CaCO3 observed as biominerals. It is universal that the sea water contents a high Mg (50mM) relative to Ca (10mM). In vivo crystallization, Mg inhibits calcite formation. For this reason, stony corals skeleton may be formed only aragonite crystals in the biocalcification. It is special in case of soft corals of which formed only calcite crystal; however, this interesting phenomenon, still uncharacterized in the marine environment, has been explored in this study using newly purified cell-free proteins isolated from the endoskeletal sclerites of soft coral. By recording the decline of pH in vitro, the control of CaCO3 nucleation and crystal growth by the cellfree proteins was revealed. Using Atomic Force Microscope, here we find that these endoskeletal cell-free proteins significantly design the morphological shape in the molecular-scale kinetics of crystal formation and those proteins act as surfactants to promote ion attachment at calcite steps. Keywords—Biomineralization, Calcite, Cell-free protein, Soft coral