An in vitro scanning microradiography study of the reduction in hydroxyapatite demineralization rate by statherin-like peptides as a function of increasing N-terminal length
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Enamel demineralization is slowed by salivary proteins that inhibit calcium hydroxyapatite (HA) demineralization. Statherin (StN43), a 43-residue phosphorylated salivary protein with primary sequence similarities to osteopontin and caseins, binds calcium and HA. The aim of this study was to identify the minimum length of the functional domain of the statherin molecule required for cariostatic function by measuring the efficacy of peptides of progressively shorter length (i.e. containing only the N-terminal 21 (StN21), 15 (StN15), 10 (StN10), or 5 (StN5) residues) to reduce HA demineralization rates (RD(HA) ). Porous HA blocks were used as enamel analogues, and were exposed to 0.1 M acetic acid at pH 4 for 120 h, rinsed, and treated with StN21, StN15, StN10, or StN5 peptides (1.88 × 10(-5) M) for 24 h, then demineralized for a further 120 h. The RD(HA) was measured, before and after peptide treatment, using scanning microradiography. Hydroxyapatite blocks treated with StN21 and StN15 demonstrated a 50-60% reduction in the RD(HA) . However, no reduction in the RD(HA) was observed following treatment with either StN10, StN5, or buffer only. The mechanism by which statherin-like peptides reduce RD(HA) may be associated with their binding to HA surfaces. Comparisons with previously published binding energies of statherin to HA also suggest that statherin-like peptides containing 15 N-terminal residues or more, are required for binding, suggesting a link between binding and demineralization reduction.