The mutans streptococci found in the oral cavity are the etiologic agents of dental caries in both humans and animals. The pathogenicity of the mutans streptococci is related to its ability to colonize enamel surfaces and generate lactic acid from the metabolism of carbohydrate substrates, especially sucrose. The long term goal of these studies is to understand at the molecular level how surface proteins of the mutans streptococci are expressed and function to contribute to the pathogenicity of the mutans streptococci. These studies will focus on the S. sobrinus spaA gene which encodes a major surface protei antigen called SpaA that is extracellularly expressed and has been cloned in Escherichia coli. SpaA-like proteins are expressed by all species of the mutans streptococci with the exception of Streptococcus rattus and includes antigen I/II of Streptococcus mutans. Antigen I/II functions in the initial adherence of S. mutans to tooth surfaces and antibodies against antigen I/II have been shown to be protective against dental caries. Recombinant SpaA (rSpaA) protein is predominantly localized in E. coli to the periplasmic space. The goal of these studies is to use the periplasmic localization of rSpaA protein to analyze using gen fusion technology the mechanism of secretion of the S. sobrinus SpaA protein and to develop a shuttle vector for the secretion of anti-cariogenic enzymes or vaccine molecules by oral streptococci. Gene fusions of E. coli alkaline phosphatase to amino-terminal sequences of the spaA gene and mutagenesis studies will be used to localize signals within the structure of the SpaA protein required for efficient transport of the SpaA protein across the cytoplasmic membrane of E. coli. The information obtained from these studies will be used to construct an E. coli- streptococcus shuttle vector that can be used for secretion of therapeutic proteins against dental caries by streptococci that normally inhabit the oral cavity. Streptococcal strains containing the secretion shuttle vector will be evaluated in an animal model for their ability to colonize the oral cavity.
