Abstract
Understanding the interactions between the protein collagen and hydroxyapatite is of high importance for understanding biomineralization and bone formation. Here, we undertook a reductionist approach and studied the interactions between a short peptide and hydroxyapatite. The peptide was selected from a phage-display library for its high affinity to hydroxyapatite. To study its interactions with hydroxyapatite, we performed an alanine scan to determine the contribution of each residue. The interactions of the different peptide derivatives were studied using a quartz crystal microbalance with dissipation monitoring and with single-molecule force spectroscopy by atomic force microscopy. Our results suggest that the peptide binds via electrostatic interactions between cationic moieties of the peptide and the negatively charged groups on the crystal surface. Furthermore, our findings show that cationic residues have a crucial role in binding. Using molecular dynamics simulations, we show that the peptide structure is a contributing factor to the adhesion mechanism. These results suggest that even small conformational changes can have a significant effect on peptide adhesion. We suggest that a bent structure of the peptide allows it to strongly bind hydroxyapatite. The results presented in this study improve our understanding of peptide adhesion to hydroxyapatite. On top of physical interactions between the peptide and the surface, peptide structure contributes to adhesion. Unveiling these processes contributes to our understanding of more complex biological systems. Furthermore, it may help in the design of de novo peptides to be used as functional groups for modifying the surface of hydroxyapatite.
Highlights
By comparing to protein databases, they showed that this peptide comprises two sections, which are related to bacterial phosphate-binding enzymes.[26]
The peptide solution was circulated in a flow cell over a commercially available quartz crystal microbalance with dissipation monitoring (QCM-D) sensor coated with HAp nanoparticles
As HAp comprises calcium phosphate, all measurements were performed in TRIS buffer rather than phosphate-buffered saline (PBS) to avoid possible interactions between the peptide and phosphate ions in the solution
Summary
Bones and dental tissues are composite materials that comprise an organic phase of mainly collagen type I fibrils and an inorganic phase of hydroxyapatite (HAp) crystals.[1−3] Like many other biocrystals, the remarkable mechanical properties of bones are achieved by their complex and hierarchical structure.[4−6] The process of biomineralization is predominantly thought to be a nonclassical crystallization pathway. Short peptides are frequently used as model systems to study this process For this purpose, phage display is commonly used to identify HAp-binding peptide sequences.[18−20] Chung et al.[20] investigated HAp-binding peptides derived from phage display and found that species with high affinity contain numerous hydroxylated residues. By comparing to protein databases, they showed that this peptide comprises two sections, which are related to bacterial phosphate-binding enzymes.[26] Weiger et al.[27] used surface plasmon resonance (SPR) analysis and showed that the SVSV moiety binds HAp while the remaining sequence adheres less potently They suggested that the SVSV subset of the peptide was the binding site and that the remainder of the sequence has a structural role that stabilizes the interaction. Using Fourier-transform infrared spectroscopy (FT-IR) along with MD simulations, we were able to deduce how the peptide secondary structure takes part in the adhesion mechanism
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