Streptococcus mutans-induced caries formation continues to be a major problem in developed and developing nations which, according to the World Health Organization, impacts 60-90% of children world-wide (128). Despite widespread water fluoridation and the implementation of educational programs aimed at improving oral health in the United States, recent reports reveal no significant improvement in the prevalence or severity of dental caries in the primary dentition (64, 120). Moreover, approximately 90% of adult Americans have dental caries in their permanent teeth, contributing to the nation's estimated costs for dental treatment that exceeded $70 billion in 2002 (44). Since the survival and virulence of S. mutans is directly related to the availability and transport of essential metal ions in the plaque environment, particularly iron and manganese, metal ion uptake mechanisms represent attractive targets for drug design aimed at combating cavities. In the present grant application, we profess a novel approach to alleviating tooth decay that is centered on investigating global virulence gene regulation by the S. mutans SloR metalloregulatory protein. During the previous grant term, we confirmed SloR-dependent repression of S. mutans metal ion transport genes and virulence factors when sustainable levels of manganese are achieved (such as during a mealtime), and loss of this repression when metal ions become limiting (such as between meals). These observations led us to hypothesize that enhanced SloR repression at physiological manganese concentrations will attenuate S. mutans virulence gene expression and impede the process of cariogenesis. This application sets out to address this hypothesis by elucidating the structural basis for SloR activation and DNA binding in S. mutans using molecular and biochemical approaches. Crystallographic analysis of the wild-type and mutant SloR protein coupled with DNA footprinting and DNA bending experiments will elucidate the details of the SloR:DNA interaction, and in vivo experiments will validate SloR-mediated virulence gene regulation and its relationship with cariogenic outcome. Taken together, these studies can facilitate the design of new therapeutic agents that target SloR activity so that caries may be controlled or eliminated.
This application proposes to investigate the details of SloR-mediated virulence gene regulation in an important human pathogen, Streptococcus mutans. To this end, we will characterize the binding of a SloR metalloregulatory protein to specific conserved DNA sequences in the S. mutans genome that can facilitate the process of cavities formation. The mechanisms which promote gene activation and repression by SloR will be explored and the cariogenic potential of SloR mutant variants investigated in a germfree rat model so that ultimately SloR can be targeted for drug design to alleviate S. mutans-induced disease. The proposed research fits the mission of the NIH/NIDCR because it can promote the development of improved caries treatment and prevention strategies, and so curtail a most ubiquitous infectious disease that continues to compromise millions of human lives.
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