title: Structure and expression of an unusually acidic matrix protein of pearl oyster shells.
abstract: We report identification and characterization of the unusually acidic molluscan shell matrix protein Aspein, which may have important roles in calcium carbonate biomineralization. The Aspein gene (aspein) encodes a sequence of 413 amino acids, including a high proportion of Asp (60.4%), Gly (16.0%), and Ser (13.2%), and the predicted isoelectric point is 1.45; this is the most acidic of all the molluscan shell matrix proteins sequenced so far, or probably even of all known proteins on earth. The main body of Aspein is occupied by (Asp)(2-10) sequences punctuated with Ser-Gly dipeptides. RT-PCR demonstrated that the transcript of aspein is expressed at the outer edge of the mantle, corresponding to the calcitic prismatic layer, but not at the inner part of the mantle, corresponding to the aragonitic nacreous layer. Our findings and previous in vitro experiments taken together suggest that Aspein is responsible for directed formation of calcite in the shell of the pearl oyster Pinctada fucata.
authors.affiliation: Department of Earth and Planetary Sciences, University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Daiki
authors.initials: D
authors.lastname: Tsukamoto
authors.forename: Isao
authors.initials: I
authors.lastname: Sarashina
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Endo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001857:Bone Matrix / Q000737:chemistry* / Q000378:metabolism*; D002113:Calcification, Physiologic / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010125:Ostreidae / Q000378:metabolism*; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution
chemical_list: D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins