Despite research for more than half a century and major advances in antimicrobial therapy, diseases caused by encapsulated bacteria, including meningococci, pneumococci, Haemophilus, influenzae type B, Escherichia coli, and group B streptococci, remain a major health problem. Interest in the prevention and control of disease caused by these bacteria has been stimulated by the high morbidity and mortality of disease caused by these microorganisms, the emergence of antibiotic resistant strains, and the threat of endemic and epidemic disease. E. coli is the most common cause of neonatal meningitis associated with high mortality and serious neurological sequelae. The Kl polysaccharide is structurally identical to polysialic acid moieties on the neural cell adhesion molecule, NCAM, which may explain the weak immunogenicity of the E. coli capsule and the lack of effective vaccines, despite intensive vaccine development efforts. Indeed, it is not clear whether vaccines against the Kl capsule would be desireable. An alternative approach to disease control would be therapeutics aimed at disrupting bacterial sialic acid metabolism. This approach requires detailed information about polysialic acid synthesis and its underlying genetic regulation. Our current understanding of the kps gene cluster in E. coli Kl is at a level of sophistication wherein molecular descriptions of synthetic and regulatory mechanisms can be investigated in a unified program. Combining powerful microbial genetic approaches with molecular and biochemical methodologies suggests, for the first time, that a complete description of a membrane polysaccharide's synthesis, underlying genetic regulation, and translocation may be possible. This information will be relevant to other capsule biosynthetic systems of medical and industrial importance. Here, we propose experiments to further define the polymerase complex that is responsible for polysialic acid synthesis, to elucidate the genetic mechanisms underlying environmental regulation of capsule expression, and to begin a functional reconstitution of polymer assembly and translocation factors. These new approaches are a direct and logical continuance of our previous research to deduce a functional genetic map of the polysialic acid gene cluster.
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