Structural and Functional Analyses of the Acidic and Basic Amino Acid Repeat Sequence (DDRK) in Pif 80 from Pinctada fucata on the Aragonite Crystal Surface Using NMR

Shellfish and crustaceans use calcium carbonate (CaCO3) as a protective shell and exoskeleton. CaCO3 isa majorbiomineral component in invertebrates. The Pinctadafucata shell contains two crystal polymorphs, withouter prismatic and inner nacreous layers. Diverse shell organic materialsplay significant roles in microstructure formation with organic-inorganicinteractions. Pif 80 has a repeated acidic and basic amino acid low-complexityregion that specifically binds to aragonite crystals. In this study,we aimed to elucidate the microstructure formation mechanism by analyzingthe interaction between the low-complexity region and CaCO3. We used solution NMR to evaluate the structure and activity ofthe Pif 80 acidic region. We designed synthesis methods for aragonitenanoparticles that can be dispersed and rotated in solution. The resultsrevealed that the GDDRKDDRKG peptide has the appropriatestructure for aragonite surface binding, wherein the four carboxygroups of the Asp side chain are in the same plane, supported by Argand Lys residues. The saturation transfer difference also supportedthis structure. These results suggest that the Pif 80 acidic regionbinds the aragonite crystal surface via Asp side chains with basicresidues, providing new insights into the function of acidic and basicamino acids in biomineral formation. Wedesigned synthesis methods for aragonite nanoparticlesthat can be dispersed and rotated in a solution NMR sample. The resultsof 3D structure analysis revealed that the low-complexity region inPif 80 (DDRK) has the appropriate structure for aragonite surfacebinding, providing new insights into the function of acidic and basicamino acids in biomineral formation.

Automated summary

Shellfish and crustaceans use calcium carbonate (CaCO3) as a protective shell and exoskeleton. In this study, the interaction between the low-complexity region and CaCO3 was analyzed to elucidate the microstructure formation mechanism. The results showed that the Pif 80 acidic region binds the aragonite crystal surface via Asp side chains with basic residues, providing new insights into the function of acidic and basic amino acids in biomineral formation.