Leveraging the Capsular Polysaccharide Synthesis Pathway in Streptococcus pneumoniae as a Genetic Glycoengineering...

Engineering carbohydrates in living cells is one of the overarching goals of biology. In this Perspective, we discuss recent work in response to this challenge. Compared with eukaryotic cells, bacteria are fast-growing and genetically tractable. At the species level, glycans in prokaryotes are highly variable, contrasting with the homogeneity of surface glycans, such as capsular polysaccharides (CPSs), at the strain level. We exploited the conditional essentiality of the CPS synthesis pathway in Streptococcus pneumoniae to overcome the challenges of biochemically monitoring the engineered glycan products. While this strategy seems feasible, this glycoengineering platform is limited by the specificity of the capsule transporters and the glycosyltransferase inventories that can be introduced into the pneumococcus. Mutants that relax transporter specificity have been isolated, enabling us to inactivate otherwise essential glycosyltransferases. Ongoing work aims to harness this technology to synthesize medically relevant glycans, including Lewis antigens and tumor markers.