An Acidic Matrix Protein, Pif, Is a Key Macromolecule for Nacre Formation

Making Mother of Pearl Nacre is an iridescent layer of calcium carbonate lining the inside of shells of marine mollusks and is commonly known as “mother of pearl.” It is composed of layers of uniformly oriented crystals of aragonite (a metastable form of calcium carbonate) separated by layers of organic matrix. How the ordered structure of aragonite layers is achieved has been unclear. Suzuki et al. (p. 1388 , published online 13 August 2009; see the Perspective by Kröger ) identified two acidic matrix proteins (Pif 97 and Pif 80) that regulate nacre formation in the Japanese pearl oyster. The proteins appear to form a complex in which Pif 80 binds to aragonite and Pif 97 binds to other macromolecules in the organic matrix.