THE INTERACTIONS OF THE CELL-SURFACE P1 ADHESIN MOLECULE OF STREPTOCOCCUS-MUTANS WITH HUMAN SALIVARY AGGLUTININ

Two assays were utilized to study the interaction of P1, a cell surface adhesin molecule expressed by Streptococcus mutans, and a high molecular weight mucin-like glycoprotein found in human saliva known as salivary agglutinin. A spectrophotometric assay was used to monitor the calcium-dependent aggregation of S. mutans in the presence of fluid-phase salivary agglutinin as evidenced by a measurable decrease in optical density at 700 nm. An adherence assay was used to measure the binding of H-3-radiolabelled S. mutans to immobilized salivary agglutinin coated onto hydroxyapatite beads. The role of P1 in these interactions was assessed using P1 retainer and non-retainer strains of S. mutans as well as P1 deficient mutants. Several monoclonal antibodies which recognize different epitopes on P1 were tested for their ability to inhibit the interaction of S. mutans with salivary agglutinin in both the aggregation or adherence assays. Different monoclonal antibodies were inhibitory in each assay suggesting that the way in which P1 interacts with salivary agglutinin differs depending on whether the agglutinin is fluid-phase or immobilized. Competitive inhibition of aggregation and adherence reactions utilizing full-length and recombinant-specified P1 polypeptides was performed as well.