NMR studies of a novel calcium, phosphate and fluoride delivery vehicle-αS1-casein(59–79) by stabilized amorphous calcium fluoride phosphate nanocomplexes

The repair of early tooth enamel lesions has been recently demonstrated by tryptic phosphopeptides derived from milk caseins that associate with amorphous calcium phosphate (ACP) forming stable complexes. These casein phosphopeptides (CPP), containing the cluster sequence–Ser(P)–Ser(P)–Ser(P)–Glu–Glu–, form calcium phosphate delivery vehicles that retard enamel demineralization and promote remineralization. Recently, we have shown that these peptides also stabilize calcium fluoride phosphate as soluble complexes. These complexes designated CPP–ACFP, have the potential to provide superior clinical efficacy in preventing dental caries and treating and repairing early stages of disease. In an approach to determine the ultrastructure of the casein phosphopeptide–amorphous calcium fluoride phosphate complexes, we have studied the structure of the predominant peptide αS1-CN(59–79) bound to ACFP using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction. The αS1-CN(59–79) peptide stabilized calcium fluoride phosphate as amorphous nanocomplexes with a hydrodynamic radius of 2.12±0.26 nm. The nanocomplexes exhibited stoichiometry of one peptide to 15 calcium, nine phosphate and three fluoride ions. Sequence-specific resonance assignments were determined for the peptide αS1-CN(59–79) complexed to the ACFP. The secondary structure of the peptide αS1-CN(59–79) was characterized by sequential (i, i+1), medium-range (i, i+2) nOes and Hα chemical shifts. The spectral data were compared with that of the peptide αS1-CN(59–79) bound to calcium ions, revealing that the structurally significant secondary NH and α-chemical shifts were similar.