Abstract
The shells of pearl oysters, Pinctada fucata, are composed of calcite and aragonite and possess remarkable mechanical properties. These shells are formed under the regulation of macromolecules, especially shell matrix proteins (SMPs). Identification of diverse SMPs will lay a foundation for understanding biomineralization process. Here, we identified 72 unique SMPs using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of proteins extracted from the shells of P. fucata combined with a draft genome. Of 72 SMPs, 17 SMPs are related to both the prismatic and nacreous layers. Moreover, according to the diverse domains found in the SMPs, we hypothesize that in addition to controlling CaCO3 crystallization and crystal organization, these proteins may potentially regulate the extracellular microenvironment and communicate between cells and the extracellular matrix (ECM). Immunohistological localization techniques identify the SMPs in the mantle, shells and synthetic calcite. Together, these proteomic data increase the repertoires of the shell matrix proteins in P. fucata and suggest that shell formation in P. fucata may involve tight regulation of cellular activities and the extracellular microenvironment.
Highlights
IntroductionRaw data from the LC-MS/MS were directly interrogated against the proteome derived from the draft genome of P. fucata[27]
The shell of P. fucata is composed of two layers, the prismatic layer and the nacreous layer (Fig. 1a)
The prismatic layer is composed of prisms with length of 10–40 μ m embedded in the organic sheath (Fig. 1b), and the nacreous layer is formed by stacked hexagonal nanotablets with side lengths of 0.5–3 μ m (Fig. 1c)
Summary
Raw data from the LC-MS/MS were directly interrogated against the proteome derived from the draft genome of P. fucata[27]. Proteins with mascot scores above 5.0 and at least two matched peptide fragments were considered to be valid and were analyzed by BLAST, SMART and InterProScan. In addition to controlling CaCO3 crystallization process proteins, proteomic analysis suggests that diverse SMPs of P. fucata contain extracellular matrix-(ECM) related proteins. Diverse domains were found, including carbonic anhydrase, Glyco_hydro_18, Cu2_monooxygen, chitin-binding, complement control protein, von Willebrand factor type A, epidermal growth factor-like, tissue inhibitor of metalloproteinase, and Laminin_G_2/3. Immunohistological experiments showed localization of SMPs in the mantle cells, shells and synthetic calcite. Our results increase shell matrix proteins’ repertoires in P. fucata and may guide the further study of SMPs
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