Identification of conserved proteins from diverse shell matrix proteome in Crassostrea gigas: characterization of genetic bases regulating shell formation

Dandan Feng,Qi Li,Shaojun Du,Hong Yu,Lingfeng Kong

doi:10.1038/srep45754

Abstract

The calcifying shell is an excellent model for studying biomineralization and evolution. However, the molecular mechanisms of shell formation are only beginning to be elucidated in Mollusca. It is known that shell matrix proteins (SMPs) play important roles in shell formation. With increasing data of shell matrix proteomes from various species, we carried out a BLASTp bioinformatics analysis using the shell matrix proteome from Crassostrea gigas against 443 SMPs from nine other species. The highly conserved tyrosinase and chitin related proteins were identified in bivalve. In addition, the relatively conserved proteins containing domains of carbonic anhydrase, Sushi, Von Willebrand factor type A, and chitin binding, were identified from all the ten species. Moreover, 25 genes encoding SMPs were annotated and characterized that are involved in CaCO3 crystallization and represent chitin related or ECM related proteins. Together, data from these analyses provide new knowledge underlying the molecular mechanism of shell formation in C.gigas, supporting a refined shell formation model including chitin and ECM-related proteins.

Highlights

In order to study the phylogenetic relationships among molluscs and refine the existing biomineralization models, it is necessary to understand the repertoire involved in shell formation
shell matrix proteomes (SMPEs)-Cg3 included in the majority of SMPs stably identified from both the SMPE-Cg1 and the SMPE-Cg2, suggesting that the majority of SMPs stably identified from the SMPE-Cg1 and the SMPE-Cg2 are specially or highly expressed in mantle
These SMPE were characterized by having a high proportion of intrinsically unstructured/disordered (ID) proteins, especially repeated low-complexity domain (RLCD) proteins

Summary

Introduction

In order to study the phylogenetic relationships among molluscs and refine the existing biomineralization models, it is necessary to understand the repertoire involved in shell formation. The well-known matrix model of “chitin-silk fibroin gel proteins-acidic macromolecules” largely explained biomineralization in P. fucata from a crystal growth perspective[10,19]. While the cellular model shows that shell formation is orchestrated by cells and the extracellular matrix (ECM) and crystals are formed in haemocytes in eastern oyster, Crassostrea virginica[20,21]. A previous study of SMPE consisting of 259 SMPs (SMPE-Cg1) suggested that the matrix model may not apply to C. gigas because the absence of silk-like proteins[13]. A SMPE of C. gigas consisting of 53 SMPs (SMPE-Cg2) was published[18], providing new opportunities for comprehensive comparison and characterization of SMPs in marine molluscan. Data from this study will assist our understanding of shell biomineralization and evolution

Methods

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Discussion

Conclusion