In-depth proteomic analysis of nacre, prism, and myostracum of Mytilus shell.

Mytilus is an economically important bivalve and its shell is a biomineralized tissue with various microstructures/layers. In the present study, the shell of marine mussel, Mytilus coruscus, was analyzed and three shell layers with different morphologies and polymorphs were observed, which includes nacre, fibrous prism, and myostracum strongly attached by adductor muscles to the interior of the shell surface. In order to understand whether these different shell layers contain different shell matrix proteins (SMPs), the transcriptome sequencing of M. coruscus mantle and a parallel proteomic analysis of SMPs in the three shell layers were performed. A combination of LC–MS/MS analysis with the mantle transcriptome dataset search resulted in the identification of a total of 63 proteins from M. coruscus shell. From this protein set, fifteen, fourteen, and eight proteins were found to be unique to nacre, fibrous prism, and myostracum layers, respectively. In addition, many novel shell proteins were also identified. The data in this study could be used as a background to explore the roles of SMPs in the deposition of different shell layers (nacre vs. fibrous prism vs. myostracum), the different polymorphisms of calcium carbonate (aragonite vs. calcite); and further, the identified proteins from the myostracum could provide candidates for studying the mechanism of adductor muscle–shell attachment.