Purification of Intramineral Peptides from Cuttlebones and In Vitro Activity in CaCO3 Biomineralization

Living organisms develop functional hard structures suchas teeth,bones, and shells from calcium salts through mineralization for managingvital functions to sustain life. However, the exact mechanism or roleof biomolecules such as proteins and peptides in the biomineralizationprocess to form defect-free hierarchical structures in nature is poorlyunderstood. In this study, we have extracted, purified, and characterizedfive major peptides (CBP1-CBP5) from the soluble organic materials(SOMs) of cuttlefish bone (CB) and used for the in vitro mineralizationof calcium carbonate crystals. The SOMs induced nucleation of thecalcite phase at low concentrations and the vaterite phase at highconcentrations. The purified peptides nucleated calcite crystals andenhanced aggregation under laboratory conditions. Among five peptides,only CBP2 and CBP3 showed concentration-dependent nucleation, aggregation,and morphological changes of the calcite crystals within 12 h. Circulardichroism studies showed that the peptides CBP2 and CBP3 are in alphahelix and beta-sheet conformation, respectively, in solution. CBP1and CBP4 and CBP5 are in random coil and beta-sheet conformation,respectively. In addition, the peptides showed different sizes insolution in the absence (similar to 27 nm, low aggregation) and presence(similar to 118 nm, high aggregation) of calcium ions. Aragonite crystalswith needle-type morphologies were nucleated in the presence of Mg2+ ions in solution. Overall, exploring the activities of suchintramineral peptides from CB help to unravel the mechanism of calciumsalt deposition in nature.

Automated summary

Living organisms develop hard structures such as teeth, bones, and shells through mineralization for vital functions. The role of biomolecules like proteins and peptides in forming defect-free hierarchical structures in nature is poorly understood. This study extracted and characterized peptides from cuttlefish bone, and found that they induced the nucleation and aggregation of calcium carbonate crystals. The peptides CBP2 and CBP3 showed concentration-dependent nucleation and morphological changes in the crystals. These intramineral peptides contribute to understanding the mechanism of calcium salt deposition in nature.