Pellicle, the first stage in plaque formation, results from phenomena that occur on surfaces. For the most part, research directed towards understanding the formation of pellicle has involved investigation of host derived salivary glycoproteins. The recent demonstration of the presence of active glucosyltransferase in pellicle on tooth surfaces suggests that the pathogenic potential of plaque may begin developing before pellicle is colonized by bacteria. The formation of glucan by GTF adsorbed to tooth surfaces adds a new dimension to the possible role of this enzyme as a virulence factor of Streptococcus mutans. Most of the research on GTF enzymology has been carried out in solution. However, results of our preliminary studies show that GTF expresses enhanced activity when adsorbed onto hydroxylapatite (HA) surfaces. Furthermore, the enzyme adsorbs with higher efficiency and expresses even greater enhancement of activity when exposed to saliva coated hydroxylapatite (sHA). The long term objectives of this proposal therefore, are to determine the kinetic properties of GTF adsorbed onto the surfaces of HA and sHA, and to characterize the interactions between GFT and salivary components adsorbed onto HA. First, the initial rate kinetics of purified S. mutans GTF's will be compared in solution, adsorbed to HA, and adsorbed to sHA. Second, the products produced by free and adsorbed GTF will be characterized. Third, we will attempt to isolate and identify the GTF adsorbed to sHA. Fourth, the biochemical and biophysical nature of the interactions between GTF and adsorbed salivary molecules will be examined. Finally, in vitro adherence assays will be conducted to investigate the potential role of salivary GTF interactions in the adhesion of oral streptococci to tooth surfaces. The approaches proposed here attempt to explore the interactions of glucosyltransferases and saliva coated surfaces; interactions that could be of critical importance in pellicle and plaque formation. The formation of glucan on the tooth surface, in advance of bacterial colonization, could have a profound influence on the biology of pellicle and on the subsequent colonization of the tooth surface by microorganisms.
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