SUMMARY Despite substantial progress in prevention and treatment, dental caries, commonly known as tooth decay or cavities, remains one of the most common and costly infectious diseases worldwide. According to the CDC, associated health care costs USA tens of billions of dollars annually. Novel, comprehensive strategies are needed to effectively combat caries pathogenesis. Cariogenic bacteria form tenacious biofilms on the surface of teeth known as dental plaque. Supported by R01 DE019452, we have over the past six years generated seminal evidence that biofilm regulatory protein BrpA, a multi-functional surface- associated protein, plays a critical role in regulation of Streptococcus mutans cell envelope biogenesis and biofilm formation and its ability to cause carious lesions. The overall goals of this competitive renewal are to uncover the complexity of the molecular mechanisms that govern the expression of brpA and the mechanisms how BrpA mediates intra- and inter-species biofilm formation, and to explore the potential of the lead small molecules in targeting BrpA and modulation of S. mutans virulence. We will use an integrative approach including various modern molecular, biochemical and bioinformatics techniques to identify the transcriptional and post-transcriptional factors that govern the regulation of brpA expression, and to determine the different binding epitopes and build the ligand-protein complex model to guide structural and functional analysis of BrpA. In addition, we will use organic chemistry along with various function assays and in vivo rat caries model to optimize the efficacy and selectivity of the selected lead small inhibitory molecules against S. mutans and to explore their potential in novel anticaries strategy. Successful implementation of this proposal could prove to be major advances in our understanding of BrpA in S. mutans pathophysiology, which could ultimately be applied to the LCP proteins in other Gram-positive bacteria. The findings on small molecules are expected to provide a solid foundation for the development of novel strategies against S. mutans and human dental caries.