Streptococcus mutans, the etiologic agent of dental caries, possesses several glucan binding proteins (GBPs) which contribute to its ability to adhere to, and colonize, tooth surfaces. The enzymatic (GBPs) are the glucosyltransferases (GTFs) which catalyze the synthesis of the glucans. The nonenzymatic (GBPs) are thought to contribute to adherence, aggregation, and the coherence of plaque but their roles are not as well documented. Thus, despite the general understanding of S. mutans pathogenesis, the precise contributions and necessity of the multiplicity of GBPs have yet to be determined. Perhaps as a consequence, there are a lack of clinical measures to specifically interfere with these S. mutans virulence factors. It has been found that the inactivation f gbpA, a gene encoding a nonenzymatic GBP, results in a change in virulence in a rat model and the accumulation of variant organisms which have undergone a recombination between the contiguous gtfB and gtfC genes to form a hybrid gtfBC. The GTF recombinants produce decreased amounts of glucan relative to the wild type. It is proposed that the inactivation of gbpA leads to a change in plaque structure and this in turn brings about a selective retention of GTF recombinants. The following specific aims test this hypothesis within the context of examining the contribution of individual GBPs to the formation of the plaque matrix. 1) Determine whether the in vivo accumulation of GTF recombinants among the GbpA mutants is due to an increased frequency of recombination or is due to selection forces, and investigate the molecular mechanism of he recombination. 2) Genetically engineer a strain of S. mutans that overexpresses GbpA by introducing multiple copies of gbpA into the organism. 3) Test the genetically engineered GbpA++ and GbpA+++ overexpresser in a rat model to examine the effects on colonization, caries development, and accumulation of GTF recombinants. 4) Make fusion proteins containing the glucan binding domains of the S. mutans GTF-I, GTF-SI, and GTF-S and determine their affinities for dextran and mutan. Compare the results with those obtained for GbpA. 5) Determine if the DNA upstream of gbpA encodes products that affect the expression or distribution of the glucosyltransferases by examining an insertional mutant of S. mutans LT11 that possesses increased levels of cell surface GTFs. Overall these studies represent a novel approach which targets GbpA as a mechanism for reducing glucosyltransferase activity and thereby the virulence of S. mutans.
