Mucins and Molluscan Calcification

Abstract

A cDNA expression library constructed from mantle tissue mRNA of the Mediterranean fan mussel Pinna nobilis was screened with antibodies raised against the acetic acid-soluble shell matrix of the same species. This resulted in the isolation of a 2138-base pair cDNA, containing 13 tandem repeats of 93 base pairs. The deduced protein has a molecular mass of 66.7 kDa and a isoelectric point of 4.8. This protein, which is enriched in serine and proline residues, was overexpressed, purified, and used for producing polyclonal antibodies. Immunological in situ and in vitro tests showed that the protein is localized in the nacreous aragonitic layer of P. nobilis, but not in the calcitic prisms. Because this protein of the nacre of P. nobilis exhibits some mucin-like characteristics, we propose the name mucoperlin. This is the first paper reporting the cloning of a molluscan mucin and the first molecular evidence for the involvement of a mucin in molluscan calcification. This finding corroborates our previous hypothesis that some of the proteinaceous constituents of the molluscan shell matrix would derive from mucins, common to many metazoan lineages of the late Precambrian (Marin, F., Smith, M., Isa, Y., Muyzer, G. and Westbroek, P. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 1554 -1559). The adaptation of an ancestral mucin to a new function, the regulation of the mineralization process, may be one of the molecular events, among others, that would explain the simultaneous emergence of organized calcification in many metazoan lineages during the Cambrian explosion.The skeletons produced by molluscs to protect and support their soft bodies are organo-mineral amalgamates (1, 2) exhibiting a high degree of order at the nanoscale (3). As a rule, the mineralized structure has mechanical properties far superior to each of its constituent components. A well known example is mother-of-pearl or nacre. Its micron-sized compact brick wall texture is more than 1000 times tougher than the chemically precipitated counterpart, aragonite (4).A complex biochemical machinery is required for the production of these highly ordered biominerals. Specialized microenvironments must be created to accommodate the growing minerals (1, 5). The constituent ions as well as macromolecules capable of directing and fine-tuning the crystallization must be supplied, while waste products of crystallization have to be removed and deleterious precipitations avoided. The actual biomineralization process follows as a remarkable case of selforganization, with the densely packed organic-inorganic composite emerging as the final product. Furthermore, the organisms must deploy upstream the calcification, signal transmitters (6, 7), and transcription factors (8, 9) able to switch their biomineralizing machineries on and off.Despite its complexity, it would appear as though the skeleton-forming machinery evolved with remarkable facility. The skeletons of many animal phyla were installed in less than 30 million years, since the beginning of the Cambrian, 544 million ...

Evolution of Nacre: Biochemistry and Proteomics of the Shell Organic Matrix of the Cephalopod Nautilus macromphalus

“…This one-residue polymorphism could be explained by the presence of two isoforms of a particular domain in different matrix proteins or the occurrence of a repeat within the same protein as already observed for mucoperlin. [43] We also noticed that the 492.26 and 729.38 m/z peptides share identical internal sequences (DSSVLT).…”

“…Three peptides match with mucoperlin ( Figure 6 D), a mucin-like protein from Pinna nobilis nacre. [43] Furthermore, weak similarities are observed between two peptides of the AIM and low-complexity sequences from MSI31 and MSI60 (Figure 6 E), but these similarities might be fortuitous as a result of the bias due to the dominance of a single amino acid. Surprisingly, all of the few similarities detected are with shell proteins of bivalve, and not gastropod, origin.…”

Cloning and Characterization of Prisilkin-39, a Novel Matrix Protein Serving a Dual Role in the Prismatic Layer Formation from the Oyster Pinctada fucata

“…1), GYS region I is characterized by 10 tandem repeats of a 12-amino acid sequence GGY(G/S)GY(G/S)YGYP(T/A). To our knowledge, there are rare reports of this kind of motif arrangement in molluscs, being found thus far solely in Lustrin A and mucoperlin (3,27). Although the significance of the repeated sequence has not been clarified, it may be related to the regular arrangement of atoms to the repeated structure of polymers in the insoluble organic framework such as chitin (13,60).…”

“…The reason for the transition of the shell layers is an intriguing question, but the answer remains unclear. One point to mention is the previous finding that an organic sheet, sandwiched between the prismatic layer and the nacreous layer, has been demonstrated by immunohistochemistry (27,28). Because the organic sheet interacts simultaneously with both calcified layers as the only intermedium in-between, it is considered to be, to some extent, responsible for particular steps during the polymorphic transition.…”

A Novel Protein Tightly Bound to Bacterial Magnetic Particles in Magnetospirillum magneticum Strain AMB-1

“…Organic molecules acting as templates that facilitate crystal formation have been isolated from demineralized materials (25)(26)(27) and organic matrix associated with mineral surfaces (28,29). Direct evidence of biomineral formations by proteins has been reported in calcium carbonate (26,27), silica (25,30), and hydroxylapatite (24).…”