Phosphorylated amelogenin N-terminal peptides regulate calcite crystal cluster formation in a water–acetonitrile system

Abstract

The structure of biomolecules play an important role in biomineral formation and studies about the regulation behavior of biominerals by changing biomolecular structures are of great help in understanding biomineralization phenomena. In this study, using the N-terminal of amelogenin as a model molecule, we studied its secondary structure change in H₂O and 30% acetonitrile–H₂O (30% Ace–H₂O), and the regulation of calcite growth by phosphorylated amelogenin N-terminal (P) and non-phosphorylated amelogenin N-terminal (NP) with different secondary structures. We found that both peptides show a random coil conformation in H₂O, which changes into an α-helix and β-sheet mixed conformation in 30% Ace–H₂O, and a random coil and α-helix mixed conformation after adding Ca²⁺. Addition of the P peptide to the H₂O crystallization system can yield calcite with occluded peptides while the NP peptide shows little effect on calcite growth. However, the P peptide can promote the dimers, helix trimers or helix crystal clusters formation while the growth habits of calcite can be hardly influenced by NP peptides in 30% Ace–H₂O. Besides, the α-helix structure of the P peptide can provide more nucleation sites for calcium carbonate and promote the helical growth of the calcite crystal in 30% Ace–H₂O, while the random coil conformation in H₂O leads to electrostatic adsorption on the calcite surface and occlusion inside calcite crystals. This work demonstrated that the function of phosphorylated organic additives can be enhanced by changing the secondary structure of the organic matrix and may provide a new strategy for novel crystal synthesis.