Structure and expression of an unusually acidic matrix protein of pearl oyster shells

Biochem Biophys Res Commun. 2004 Aug 6;320(4):1175-80. doi: 10.1016/j.bbrc.2004.06.072.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Bone Matrix / chemistry*
  • Bone Matrix / metabolism*
  • Calcification, Physiologic / physiology
  • Calcium-Binding Proteins / chemistry*
  • Calcium-Binding Proteins / metabolism*
  • Extracellular Matrix Proteins / chemistry*
  • Extracellular Matrix Proteins / metabolism*
  • Hydrogen-Ion Concentration
  • Molecular Sequence Data
  • Organ Specificity
  • Ostreidae / metabolism*
  • Protein Conformation
  • Sequence Homology, Amino Acid
  • Tissue Distribution


  • Calcium-Binding Proteins
  • Extracellular Matrix Proteins

Associated data

  • GENBANK/AB094512