A simple periodic peptide derived from Pinctada fucata Pif80 protein induces aragonite nucleation in magnesium absence

Pif80 protein is associated with nacre formation in the Akoya pearl oyster. The influence of Pif2, a 32-mer peptide derived from Pif80, on calcium carbonate polymorphism, crystal orientation, morphology, and the induction of aragonite was investigated. X-ray diffraction (XRD) analyses reveal that Pif2, in the presence of a polydiacetylene (PDA) template, enhances calcite crystal nucleation on the (012) plane while suppressing the nucleation from the (104) face. Scanning electron microscopy (SEM) images illustrate the Pif2 concentration-dependent impact on calcite crystal morphology, with higher concentrations leading to deformed habits and distinct crystal faces. The peptide induces aragonite formation, even under conditions conducive to calcite growth, as evidenced by SEM and transmission electron microscopy (TEM) studies, on the condition that an appropriate template is provided. Time-dependent SEM observations trace the transformation of amorphous calcium carbonate to calcite/aragonite, highlighting Pif2's role in this process. Experiments with geological aragonite templates affirm the preferential formation of aragonite in the presence of Pif2, as confirmed by TEM and focused ion beam scanning electron microscopy (FIBSEM) analyses. The results underscore Pif2's pivotal role in orchestrating the biological control of polymorphism in Pinctada fucata, providing valuable insights for biomineralization studies and biomimetic materials design.