Biosynthesis, Structure and Function of Cell Wall in Streptococcus Mutans

The cell wall of many species of Lactobacillales consists of multiple peptidoglycan layers decorated with serotype-specific polysaccharides that are characterized by the presence of rhamnose. These glycopolymers are attractive vaccine candidates due to their conserved expression in medically important Lactobacillales and absence in humans. Furthermore, the cell wall biosynthetic machinery is an historically preferred target for the development of novel antimicrobials. The goals of this project are to understand the structures, biosynthesis and functions of the serotype-specific glycans expressed by the human pathogen Streptococcus mutans. This bacterium is a key etiological agent of human dental caries, and has been also implicated in periodontal disease, bacteremia and infective endocarditis. Based on the chemical structures of serotype-specific polysaccharides, S. mutans is classified into serotypes c, e, f and k with approximately 70-80% of strains found in the oral cavity classified as serotype c. Although carbohydrate structures have been reported for all S. mutans serotypes, our recent insights into the structure of the serotype c polysaccharide indicates that the functionally important modification, glycerol phosphate, was overlooked, possibly due to its loss during the purification steps. This new finding justifies a re-examination of the chemical structure of the carbohydrates. Moreover, little is known about the multienzyme processes involved in glycopolymer synthesis and its biological function in S. mutans. Our preliminary findings revealed that the glycerol phosphate modifications play important roles in S. mutans morphology, autolysis, resistance to antimicrobials and biofilm formation. To accomplish our goals, we will employ streptococcal genetics, in vitro enzymology, analytical chemistry, mass spectrometric analysis of phospholipids, NMR methods and different methods of microscopy including AFM-based nanomechanics. Successful outcomes will guide studies of cell wall biogenesis in other important Gram-positive bacteria and the development of novel strategies to treat Gram-positive bacterial infections.