PMID:15994301

Citation	Marin, F, Amons, R, Guichard, N, Stigter, M, Hecker, A, Luquet, G, Layrolle, P, Alcaraz, G, Riondet, C and Westbroek, P (2005) Caspartin and calprismin, two proteins of the shell calcitic prisms of the Mediterranean fan mussel Pinna nobilis. J. Biol. Chem. 280:33895-908
Abstract	We used the combination of preparative electrophoresis and immunological detection to isolate two new proteins from the shell calcitic prisms of Pinna nobilis, the Mediterranean fan mussel. The amino acid composition of these proteins was determined. Both proteins are soluble, intracrystalline, and acidic. The 38-kDa protein is glycosylated; the 17-kDa one is not. Ala, Asx, Thr, and Pro represent the dominant residues of the 38-kDa protein, named calprismin. An N-terminal sequence was obtained from calprismin. This sequence, which comprises a pattern of 4 cysteine residues, is not related to any known protein. The second protein, named caspartin, exhibits an unusual amino acid composition, since Asx constitutes by far the main amino acid residue. Preliminary sequencing surprisingly suggests that the first 75 N-terminal residues are all Asp. Caspartin self-aggregates spontaneously into multimers. In vitro tests show that it inhibits the precipitation of calcium carbonate. Furthermore, it strongly interferes with the growth of calcite crystals. A polyclonal antiserum raised against caspartin was used to localize this protein in the shell by immunogold. The immunolocalization demonstrates that caspartin is distributed within the prisms and makes a continuous film at the interface between the prisms and the surrounding insoluble sheets. Our finding emphasizes the prominent role of aspartic acid-rich proteins for the building of calcitic prisms among molluscs.
Links	PubMed Online version:10.1074/jbc.M506526200
Keywords	Amino Acid Sequence; Animals; Bivalvia/chemistry; Bivalvia/physiology; Calcium Carbonate/metabolism; Crystallization; Electrophoresis; Glycoproteins/chemistry; Glycoproteins/isolation & purification; Immunoassay; Molecular Sequence Data
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
PINNO:CPRM		GO:0031215: shell calcification	ECO:0000314:		P		Figure 9A: Shows in vitro inhibition of the precipitation of CaCO3 by caspartin; this protein is dose dependently an inhibitor of shell calcification	complete CACAO 9794

References

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