Nacre evolution: a proteomic approach.

From an evolutionary viewpoint, the molluscan nacre constitutes a fascinating object. This microstructure appeared early, in the Lower Cambrian period, about 530 million years ago, and since then, has been kept unchanged until today. Nacre is restricted to the conchiferan mollusks, where it occurs in t least three main classes, bivalves, gastropods and cephalopods. The aim of the present study is to investigate whether all nacres are built from the same "macromolecular tools", proteins of the nacre matrix. To this end, we studied three new nacre models, the freshwater bivalve Unio pictorum, the cephalopod Nautilus macromphalus, and the gastropod Haliotis asinina, to which we applied a combined biochemical and proteomic characterization of their respective nacre matrices. The results of our approach, that can be defined as "shellomics" (proteomics applied to shell proteins) shed a new light on the macroevolution of nacre matrix proteins and on the in vitro design of nacre-like biomaterials.