Biomineralization and Size Control of Stable Calcium Phosphate Core–Protein Shell Nanoparticles: Potential for Vaccine Applications

Abstract

Calcium phosphate (CaP) polymorphs are nontoxic, biocompatible and hold promise in applications ranging from hard tissue regeneration to drug delivery and vaccine design. Yet, simple and robust routes for the synthesis of protein-coated CaP nanoparticles in the sub-100 nm size range remain elusive. Here, we used cell surface display to identify disulfide-constrained CaP binding peptides that, when inserted within the active site loop of E. coli Thioredoxin 1 (TrxA), readily and reproducibly drive the production of nanoparticles that are 50–70 nm in hydrodynamic diameter and consist of an approximately 25 nm amorphous calcium phosphate (ACP) core stabilized by the protein shell. Like bone and enamel proteins implicated in biological apatite formation, peptides supporting nanoparticle production were acidic. They also required presentation in a loop for high affinity ACP binding since elimination of the disulfide bridge caused a nearly 3-fold increase in hydrodynamic diameters. When compared to a commercial aluminum phosphate adjuvant, the small core-shell assemblies led to a 3-fold increase in mice anti-TrxA titers three weeks post-injection, suggesting that they might be useful vehicles for adjuvanted antigen delivery to dendritic cells.

Peptide-based synthetic vaccines

“…Materials such as aluminum oxide, 78 gold 65 and calcium phosphate 79 have been used for peptide-based vaccine delivery. In contrast, lipid-based particles are usually biocompatible and biodegradable.…”

Turning a water and oil insoluble cisplatin derivative into a nanoparticle formulation for cancer therapy

“…DOPA, known to bind to metal ions such as calcium and platinum, was used to stabilize the CDDP-I precipitate and permitted control over the nanoprecipitates’ size. The surfactants Igepal and Triton X-100 were used for a similar purpose [14–16]. Without DOPA, the formation of the cores was not well controlled and large aggregates were formed after demulsification with ethanol.…”

A Review on Recent Patents and Applications of Inorganic Material Binding Peptides

“…So far, a range of biomimetic peptides showing specific affinity and molecular recognition for inorganic nanomaterials including metals, metal oxides, minerals, magnetic and semiconductor materials, carbon or polymer based materials have been isolated . Further, these material specific peptides have been used for synthesizing simple to complex bio-or nano-materials, mediating the controlled biomineralzation process, directing self-assembly and nanofabrication of ordered structures, facilitating the immobilization of functional biomolecules and for constructing inorganicinorganic or organic-inorganic nano hybrids [50][51][52][53][54][55][56][57][58][59][60][61][77][78][79].…”

“…From there on, phage or cell surface displayed (7-15mers) libraries have become ubiquitous in selecting and screening peptides having strong *Address correspondence to this author at the Interdisciplinary Biomedical Research Centre, Nottingham Trent University, Clifton Lane, NG11 8NS, Nottingham, UK; Tel: +44-115-8486695; E-mail: Carole.Perry@ntu.ac.uk affinity towards a range of inorganic material surfaces such as metals (Ag [19][20][21], Au [22,23], Pt [24], Pd [25]), metal oxides (SiO2 [26][27][28][29][30], ZnO [31,32], TiO2 [33][34][35], Fe2O3 [36,37], IrO2 [38], Al2O3 [24,39], Cu2O [31]), minerals (calcite, hydroxyapatite, graphite, mica, sapphire) [40][41][42], semiconductors (CdS, GaN, GaAs and ZnS) [43][44][45], carbon materials (graphene, carbon nanotubes) [46,47] and polymer materials [48,49]. These isolated peptides have many practical applications in biomineralization [32,50,51], synthesis and fabrication of inorganic nanomaterials [40,[52][53][54][55][56]…”