Hyriopsis cumingii Hic52-A novel nacreous layer matrix protein with a collagen-like structure.

Nacre is a product of a precisely regulated biomineralization process and a major contributor to the luster of pearls. Nacre is composed of calcium carbonate and an organic matrix of proteins that is secreted from mollusc mantle tissue and is exclusively associated with shell formation. In this study, hic52, a novel matrix protein gene from mantle of Hyriopsis cumingii, was cloned and functionally analyzed. The full-length cDNA of hic52 encoded 542 amino acids and contained a signal peptide of 18 amino acids. Excluding the signal peptide, the theoretical molecular mass of the polypeptide was 52.2kDa. The predicted isoelectric point was 10.37, indicating a basic shell protein. The amino acid sequence of hic52 featured high proportion of Gly (28.8%) and Gln (12.4%) residues. The predicted tertiary structure was characterized as having similarities to collagen I, alpha 1 and alpha 2 in the structure. The polypeptide sequence shared no homology with collagen. The hic52 expression pattern by quantitative real-time PCR and in situ hybridization exhibits at the dorsal epithelial cells of the mantle. Expression increased during the stages of pearl sac development. The data showed that hic52 is probably a framework shell protein that mediates and controls the nacreous biomineralization process.

A Novel Matrix Protein Hic31 from the Prismatic Layer of Hyriopsis Cumingii Displays a Collagen-Like Structure.

In this study, we clone and characterize a novel matrix protein, hic31, from the mantle of Hyriopsis cumingii. The amino acid composition of hic31 consists of a high proportion of Glycine residues (26.67%). Tissue expression detection by RT-PCR indicates that hic31 is expressed specifically at the mantle edge. In situ hybridization results reveals strong signals from the dorsal epithelial cells of the outer fold at the mantle edge, and weak signals from inner epithelial cells of the same fold, indicating that hic31 is a prismatic-layer matrix protein. Although BLASTP results identify no shared homology with other shell-matrix proteins or any other known proteins, the hic31 tertiary structure is similar to that of collagen I, alpha 1 and alpha 2. It has been well proved that collagen forms the basic organic frameworks in way of collagen fibrils and minerals present within or outside of these fibrils. Therefore, hic31 might be a framework-matrix protein involved in the prismatic-layer biomineralization. Besides, the gene expression of hic31 increase in the early stages of pearl sac development, indicating that hic31 may play important roles in biomineralization of the pearl prismatic layer.

Silkmapin of Hyriopsis cumingii, a novel silk-like shell matrix protein involved in nacre formation.

Understanding the role of matrix proteins in nacre formation and biomineralization in mollusks is important for the pearl industry. In this study, the gene encoding the novel Hyriopsis cumingii shell matrix protein silkmapin was characterized. The gene encodes a protein of 30.89kDa in which Gly accounts for 34.41% of the amino acid content, and the C-terminal region binds Ca(2+). Secondary structure prediction indicated a predominantly ß-fold and a structure typical of filamentous proteins. Real-time quantitative PCR and in situ hybridization showed that silkmapin was expressed in epithelial cells at the edge and pallial of mantle tissue, indicated that silkmapin play roles in the shell nacreous and prismatic layer formation. Further real-time PCR results indicated an involvement in pearl formation via nucleation of calcium carbonate prior to formation of the nacre.