Proteomic characterization of oyster shell organic matrix proteins (OMP)

Oysters are economically and ecologically important bivalves, with its calcareous shell and delicious meat. The shell composition is a blend of inorganic crystals and shell proteins that form an organic matrix which protects the soft inner tissue of the oyster. The objective of the study was to compare the composition of organic matrix proteins (OMP) of two phylogenetically related species: the Hong Kong oyster (Crassostrea hongkongensis) and the Portuguese oyster (Crassostrea angulata) which differ in their shell hardness and mechanical properties. C. hongkongensis shells are comparatively stronger than C. angulata. Modern shotgun proteomics has been used to understand the nature of the OMP and the variations observed in the mechanical properties of these two species of oyster shells. After visualizing proteins on the one (1DE) and two-dimensional electrophoresis (2DE) gels, the protein spots and their intensities were compared using PDQuest software and 14 proteins of C. hongkongensis were found to be significantly different (student׳s t-test; p<0.05) when compared to the C. angulata. Furthermore, shell OMP separated on 1DE gels were processed using Triple TOF5600 mass spectrometry and 42 proteins of C. hongkongensis and 37 of C. angulata identified. A Circos based comparative analysis of the shell proteins of both oyster species were prepared against the shell proteome of other shell forming gastropods and molluscs to study the evolutionary conservation of OMP and their function. This comparative proteomics expanded our understating of the molecular mechanism behind the shells having different hardness and mechanical properties.