title: A comparative study of the shell matrix protein aspein in pterioid bivalves.
abstract: Aspein is one of the unusually acidic shell matrix proteins originally identified from the pearl oyster Pinctada fucata. Aspein is thought to play important roles in the shell formation, especially in calcite precipitation in the prismatic layer. In this study, we identified Aspein homologs from three closely related pterioid species: Pinctada maxima, Isognomon perna, and Pteria penguin. Our immunoassays showed that they are present in the calcitic prismatic layer but not in the aragonitic nacreous layer of the shells. Sequence comparison showed that the Ser-Glu-Pro and the Asp-Ala repeat motifs are conserved among these Aspein homologs, indicating that they are functionally important. All Aspein homologs examined share the Asp-rich D-domain, suggesting that this domain might have a very important function in calcium carbonate formation. However, sequence analyses showed a significantly high level of variation in the arrangement of Asp in the D-domain even among very closely related species. This observation suggests that specific arrangements of Asp are not required for the functions of the D-domain.
authors.affiliation: Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. isowa@eps.s.u-tokyo.ac.jp
authors.forename: Yukinobu
authors.initials: Y
authors.lastname: Isowa
authors.forename: Isao
authors.initials: I
authors.lastname: Sarashina
authors.forename: Davin H E
authors.initials: DH
authors.lastname: Setiamarga
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Endo
mesh_terms: D000595:Amino Acid Sequence; D060105:Animal Shells / Q000378:metabolism*; D000818:Animals; D016326:Extracellular Matrix Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010802:Phylogeny; D049911:Pinctada; D021382:Protein Sorting Signals; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid
chemical_list: D016326:Extracellular Matrix Proteins; D021382:Protein Sorting Signals