Comparison of Cariostatic Efficacy of Human and Mammalian Statherins

Objectives: It has been shown that the human salivary protein statherin has cariostatic efficacy. However, the amino acid sequence of mammalian statherins varies considerably, but not at the N-terminal hydroxyapatite binding site. The aim was to measure a) the adsorption to hydroxyapatite (HAP) and b) the cariostatic efficacy of four non-human statherin sequences compared with human statherin, and, to correlate. This will give insight into the impact of statherin binding as influenced by its sequence variability on its cariostatic efficacy.
Methods: Statherin sequences of macaque, pig, sheep and cattle were obtained from a genomic sequence database. The N-terminal 21-mer of each protein was synthesised and their concentrations measured spectrophotometrically. The specific adsorption to HAP of each sequence from a 100 µMol solution of peptide onto 1 mg of HAP beads was calculated. The inhibition of demineralisation was measured using scanning microradiography (SMR) of HAP disks exposed to a pH 4.0 caries simulating solution. Both were compared with data previously obtained for human statherin, and a correlation coefficient between both datasets calculated. Secondary sequence prediction software was used to calculate the potential for α-helix formation for each.
Results: All statherin sequences showed hydroxyapatite adsorption and demineralisation inhibition as shown in Table 1. The was a positive correlation(R²=0.96) showing that those sequences with higher binding efficacy have higher demineralisation inhibition. There was little relation between helix formation predictions and either binding or cariostatic efficacy.
Conclusions: The amino acid sequence of statherins varies considerably after the initial N-terminal pentapeptide, however all similarly bind to HAP and similarly inhibit demineralisation. There is no evidence that the diet and digestive systems are related to their effectiveness. The small differences in binding correlate positively with their cariostatic efficacy, and therefore increased binding increases cariostatic efficacy. The ability of the N-terminal to form helices in its solution does not impact on either. However, it is likely that such secondary structure is only conferred following binding to HAP.