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

In mollusks, one of the most widely studied shell textures is nacre, the lustrous aragonitic layer that constitutes the internal components of the shells of several bivalves, a few gastropods, and one cephalopod: the nautilus. Nacre contains a minor or- ganic fraction, which displays a wide range of functions in relation to the biomineralization process. Here, we have biochemi- cally characterized the nacre matrix of the cephalopod Nautilus macromphalus. The acid-soluble matrix contains a mixture of polydisperse and discrete proteins and glycoproteins, which interact with the formation of calcite crystals. In addition, a few bind calcium ions. Furthermore, we have used a proteomic approach, which was applied to the acetic acid-soluble and insoluble shell matrices, as well as to spots obtained after 2D gel electrophoresis. Our data demonstrate that the insoluble and soluble matrices, although different in their bulk monosacchar- ide and amino acid compositions, contain numerous shared peptides. Strikingly, most of the obtained partial sequences are entirely new. A few only partly match with bivalvian nacre pro- teins. Our findings have implications for knowledge of the long-term evolution of molluskan nacre matrices.


An interesting feature, of these molluscan protiens , is the Tyrosinase domains which seems to be unique to molluscs, one possibility is its realtionship to hemocyanins

Tyrosinase () PUBMED:3130643 is a copper monooxygenases that catalyzes the hydroxylation of monophenols and the oxidation of o-diphenols to o-quinols. This enzyme, found in prokaryotes as well as in eukaryotes, is involved in the formation of pigments such as melanins and other polyphenolic compounds. Tyrosinase binds two copper ions (CuA and CuB). Each of the two copper ions has been shown PUBMED:1901488 to be bound by three conserved histidines residues. The regions around these copper-binding ligands are well conserved and also shared by some hemocyanins, which are copper-containing oxygen carriers from the hemolymph of many molluscs and arthropods PUBMED:2664531, PUBMED:1898774. At least two proteins related to tyrosinase are known to exist in mammals, and include TRP-1 (TYRP1) PUBMED:7813420, which is responsible for the conversion of 5,6-dihydro-xyindole-2-carboxylic acid (DHICA) to indole-5,6-quinone-2-carboxylic acid; and TRP-2 (TYRP2) PUBMED:1537334, which is the melanogenic enzyme  DOPAchrome tautomerase () that catalyzes the conversion of DOPAchrome to DHICA. TRP-2 differs from tyrosinases and TRP-1 in that it binds two zinc ions instead of copper PUBMED:7980602. Other proteins that belong to this family are plant polyphenol oxidases (PPO) (), which catalyze the oxidation
of mono- and o-diphenols to o-diquinones PUBMED:1391768; and  Caenorhabditis elegans hypothetical protein C02C2.1.

check out these proteins full of Tyrosinase 😉