Binding properties of streptococcal glucosyltransferases for hydroxyapatite, saliva-coated hydroxyapatite, and bacterial surfaces

The binding specificities of Streptococcus glucosyltransferase (Gtf) B, C and D for hydroxyapatite (HA), saliva-coated hydroxyapatite (SHA), and bacterial surfaces were examined. For HA beads the following values were obtained: (K=affinity; N=number of binding sites) GtfB, K=46×105 ml/μmol, N=0.65×10−6 μmol/m2; GtfC, K=86×105 ml/μmol, N=4.42×10−6 μmol/m2; GtfD, K=100×105 ml/μmol, N=0.83×10−6 μmol/m2. For SHA beads, the following values were obtained: GtfB, K=14.7×105 ml/μmol, N=1.03×10−6 μmol/m2; GtfC, K=21.3×105 ml/μmol, N=3.66×10−6 μmol/m2; GtfD, K=1.73×105 ml/μmol, N=8.88×10−6 μmol/m2. The binding of GtfB to SHA beads was reduced in the presence of parotid saliva, but the binding of GtfC and D was unaffected. The binding of GtfB to SHA in the presence of parotid saliva supplemented with GtfC and D was reduced when compared with its binding to SHA in the presence of parotid saliva alone. In contrast, the binding of GtfC and D to SHA was unaffected when parotid saliva was supplemented with the other Gtf enzymes. GtfB bound to several bacterial strains (Strep. mutans GS-5, Actinomyces viscosus OMZ105E and Lactobacillus casei 4646) in an active form, while GtfC and D did not bind to bacterial surfaces. It is concluded that of the three Gtf enzymes, GtfC has the highest affinity for HA and SHA surfaces and can adsorb on to the SHA surface in the presence of the other two enzymes. GtfD also binds to SHA in the presence of the other enzymes but has a very low affinity for the surface. GtfB does not bind to SHA in the presence of the other Gtf enzymes but binds avidly to bacterial surfaces in an active form. Therefore, GtfC most probably binds to apatitic surfaces, while GtfB binds to bacterial surfaces.