Statherin and Histatin 1 Reduce Parotid Saliva-Promoted <i>Streptococcus mutans</i> Strain MT8148 Adhesion to Hydroxyapatite Surfaces

Small salivary phosphoproteins – statherin (ST) and histatin 1 (HT1) – are found in the acquired enamel pellicle which modulates <i>Streptococcus mutans</i> adhesion onto dental enamel. However, their roles in <i>S. mutans</i> adhesion onto enamel surfaces are still undefined. The aim of this study was to investigate whether and how ST and HT1 affect (i) <i>S. mutans</i> adhesion and (ii) the adsorption of <i>S. mutans</i> adhesion-promoting salivary proteins onto hydroxyapatite (HA) in vitro. We fractionated human parotid saliva by adsorption to HA and further by gel filtration chromatography. Adhesion of [³H]-labeled <i>S. mutans</i> strain MT8148 onto sintered HA plates was promoted significantly (>10-fold) by high-molecular weight glycoprotein fraction (HMWGP), but not by purified ST or HT1. More interestingly, promotion of <i>S. mutans</i> adhesion onto HA by HMWGP was significantly reduced by adding purified ST or HT1 to HMWGP. [³H]-labeled <i>S. mutans</i> adhesion on HA was positively correlated to the [¹⁴C]-labeled HMWGP adsorption onto HA, which was also reduced by the addition of purified ST and HT1. Synthetic peptides corresponding to ST and HT1 reduced the parotid saliva-promoted <i>S. mutans</i> adhesion. However, removal of the negative charges in the N-terminal domains of ST and HT1 diminished their inhibitory effects on <i>S. mutans</i> adhesion promoted by parotid saliva. We conclude that ST and HT1 competitively inhibit the adsorption of salivary HMWGP, and thereby reduce <i>S. mutans</i> adhesion onto HA surfaces.