Nacre, the iridescent composite that forms pearls and the lining of some mollusk shells, is composed of layers of bricklike aragonite calcium carbonate crystals embedded in a mortar of chitin and proteins. Nature has been stingy in surrendering the secrets behind nacre’s orderly assemblage, but Japanese researchers have now discovered two proteins that are key to this process (Science, DOI: 10.1126/science.1173793). Hiromichi Nagasawa and colleagues of the University of Tokyo discovered one protein, Pif80, by searching for a protein that preferentially binds aragonite. The researchers determined that Pif80 has its origins in a precursor protein; when cleaved, the precursor releases Pif80 and the second protein, Pif97. When the researchers suppressed production of these proteins in oysters, crystal growth was slow and disordered, and the mollusks were unable to form pearly sheets of nacre. Nagasawa’s team believes that Pif80 and Pif97 form a complex that binds to other proteins and chitin, concentrates calcium carbonate, induces formation of aragonite crystals, and regulates crystal orientation.