Repaired Shells of the Pearl Oyster Largely Recapitulate Normal Prismatic Layer Growth: A Proteomics Study of Shell Matrix Proteins.

Shells of pearl oysters are natural biominerals with remarkable properties that can be repaired after damage. The repair process can be regulated by biomacromolecules, especially shell matrix proteins (SMPs). Identifying SMPs is critical for further understanding the process. Although proteomic methods have been used to reveal the complex protein mixture in mature shells, the proteomics of repaired shells after shell damage have not been reported before. In the work described here, we studied the SMPs of the repaired shells (prismatic layers) 5-20 days after shell damage in the pearl oyster Pinctada fucata by integrating transcriptomics and proteomics and then compared the microstructure difference between repaired and mature shells. Although the repaired shells are calcite, similar to mature shells, the microstructures of repaired shells during the regeneration process were different, which could simulate the embryonic shell formation process. In total, we found 49 SMPs from the repaired shells, including some proteins that exist only in mature nacreous layers. Peroxidase-like protein and β-N-acetylhexosaminidase may be important players in shell repair. In addition, SMPs have the capability to affect the CaCO3 crystallization process in vitro, altering the packing and reducing the crystallinity of the crystals. This study could improve our understanding of the shell repair process and lay the foundation for studying SMPs-controlled biomineralization.