Novel Proteins from the Calcifying Shell Matrix of the Pacific Oyster Crassostrea gigas

The shell of the Pacific oyster Crassostrea gigas is composed of more than 99% CaCO3 and of around 0.5% of occluded organic matrix. According to classical views, this matrix is supposed to regulate the shell mineral deposition. In this study, we developed one of the first proteomic approaches applied to mollusk shell in order to characterise the calcifying matrix proteins. The insoluble organic matrix, purified after demineralisation of the shell powder, was digested with trypsin enzyme, and separated on nano-LC, prior to nanospray quadrupole/time-of-flight analysis. MS/MS spectra were searched against the above 220,000 EST sequences available in the public database for Crassostrea. Using this approach, we were able to identify partial or full-length sequence transcripts that encode eight novel shell matrix proteins.