Purification and Characterization of a Vaterite-Inducing Peptide, Pelovaterin, from the Eggshells of <i>Pelodiscus </i><i>s</i><i>inensis</i> (Chinese Soft-Shelled Turtle)

Proteins play a crucial role in the biomineralization of hard tissues such as eggshells. We report here the purification, characterization, and in vitro mineralization studies of a peptide, pelovaterin, extracted from eggshells of a soft-shelled turtle. It is a glycine-rich peptide with 42 amino acid residues and three disulfide bonds. When tested in vitro, the peptide induced the formation of a metastable vaterite phase. The floret-shaped morphology formed at a lower concentration (∼1 μM) was transformed into spherical particles at higher concentrations (>500 μM). The solution properties of the peptide are investigated by circular dichroism (CD), fluorescence emission spectroscopy, and dynamic light scattering (DLS) experiments. The conformation of pelovaterin changed from an unordered state at a low concentration to a β-sheet structure at high concentrations. Fluorescence emission studies indicated that the quantum yield is significantly decreased at higher concentrations, accompanied by a blue shift in the emission maximum. At higher concentrations a red-edge excitation shift was observed, indicating the restricted mobility of the peptide. On the basis of these observations, we discuss the presence of a peptide concentration-dependent monomer−multimer equilibrium in solution and its role in controlling the nucleation, growth, and morphology of CaCO3 crystals. This is the first peptide known to induce the nucleation and stabilization of the vaterite phase in solution

Structure, Self-Assembly, and Dual Role of a β-Defensin-like Peptide from the Chinese Soft-Shelled Turtle Eggshell Matrix

Biomineral matrix formation and molecular recognition are two important processes associated with eggshell biomineralization. To understand these two processes, a major intracrystalline peptide, pelovaterin, was isolated from turtle (Pelodiscus sinensis) eggshell and its tertiary and quaternary structures were established. The global fold of pelovaterin is similar to that of human β-defensins but has a large hydrophobic core and a short hydrophilic N-terminal segment, which is not preserved in defensins. Pelovaterin exhibits strong antimicrobial activity against two pathogenic Gram-negative bacteria, Pseudomonas aeruginosa and Proteus vulgaris, and stabilizes a thin film of metastable vaterite. We show that pelovaterin self-aggregates in the form of micellar nanospheres and the aggregation in solution is entropy-driven. It is suggested that the micellar aggregation of pelovaterin is responsible for the induction and stabilization of the metastable phase by altering the interfacial energy. The results demonstrate the adaptability of an extracellular matrix protein to perform multiple tasks:  polymorph discrimination and protection of the contents of the egg against bacterial invasion