Abstract
Bivalve shell is a biomineralized tissue with various layers/microstructures and excellent mechanical properties. Shell matrix proteins (SMPs) pervade and envelop the mineral crystals and play essential roles in biomineralization. Despite that Mytilus is an economically important bivalve, only few proteomic studies have been performed for the shell, and current knowledge of the SMP set responsible for different shell layers of Mytilus remains largely patchy. In this study, we observed that Mytilus galloprovincialis shell contained three layers, including nacre, fibrous prism, and myostracum that is involved in shell-muscle attachment. A parallel proteomic analysis was performed for these three layers. By combining LC-MS/MS analysis with Mytilus EST database interrogations, a whole set of 113 proteins was identified, and the distribution of these proteins in different shell layers followed a mosaic pattern. For each layer, about a half of identified proteins are unique and the others are shared by two or all of three layers. This is the first description of the protein set exclusive to nacre, myostracum, and fibrous prism in Mytilus shell. Moreover, most of identified proteins in the present study are novel SMPs, which greatly extended biomineralization-related protein data of Mytilus. These results are useful, on one hand, for understanding the roles of SMPs in the deposition of different shell layers. On the other hand, the identified protein set of myostracum provides candidates for further exploring the mechanism of adductor muscle-shell attachment.
Highlights
Mollusk shell, primarily consisting of calcium carbonate crystals together with organic matrix, has been investigated as a typical biomineralization model for dozens years [1,2,3,4]
The top layer of acid-soluble matrix (ASM)-A, adductor muscle scar (AMS), and AMS-P, corresponding to the nacre, myostracum, and fibrous prism, respectively, was scraped off and the shell matrices were extracted for proteomic analysis
The amount of total organic matrix from shell layers represents an average of 3.4% by weight of the shell powder, and the highest content of organic material was presented in nacre (5.3%), followed by myostracum (3.5%) and fibrous prism (1.9%)
Summary
Primarily consisting of calcium carbonate crystals together with organic matrix, has been investigated as a typical biomineralization model for dozens years [1,2,3,4]. It is well known that there are three major calcium carbonate minerals (calcite, aragonite, and vaterite) with the same principal composition, despite the different structures [5]. Of these minerals, the two most thermodynamically stable structures, calcite and aragonite, are deposited extensively as biominerals. Most of the adult shell of bivalves found in nature are composed of PLOS ONE | DOI:10.1371/journal.pone.0133913. Most of the adult shell of bivalves found in nature are composed of PLOS ONE | DOI:10.1371/journal.pone.0133913 July 28, 2015
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